JP4849556B2 - Imaging apparatus and control method thereof - Google Patents

Description

  2. Description of the Related Art Conventionally, imaging devices such as digital cameras and digital video cameras that use a CCD or CMOSAPS as an imaging device and record captured images are widely known. Many of these imaging devices measure the brightness of the subject to be photographed to control the photographing sensitivity so that the overshoot of the photographed image is reduced and not too dark.

  Sensitivity control means include aperture control for controlling the amount of light incident on the image sensor, shutter control for controlling the exposure time of the image sensor, and the like. In addition, the brightness of the captured image is also controlled by amplifying the signal in the imaging apparatus.

  As these signal amplification means, there are mainly analog signal amplification in an image sensor or AFE (analog front end) and digital signal amplification in an image signal processing circuit. In general, the signal amplifying means is provided at a plurality of locations in the imaging apparatus.

  By the way, the amount of noise appearing in an image obtained by the imaging apparatus varies depending on which amplification means in the imaging apparatus amplifies. In general, it is assumed that signal amplification causes less noise to appear in an image when it is performed in the previous stage in the imaging apparatus.

  For example, in FIG. 1 to be described later, the reason will be described by taking as an example a case where some electrical noise is mixed between the amplifying means 105 and the amplifying means 107. In this case, the signal amplified by the amplifying unit 107 amplifies the electrical noise by the signal amplification factor of the amplifying unit 107 as compared with the signal amplified by the amplifying unit 105.

  In this case, noise in the A / D converter 106 is mainly amplified. Under such circumstances, generally, when signal amplification is performed in an imaging apparatus, if signal amplification is performed on the side closer to the photoelectric conversion element, an image with good image quality can be obtained against noise mixed in the middle. .

  However, when the signal is amplified in an analog manner in the imaging apparatus, the output amplitude of the amplifying unit becomes large, and the signal amplitude handled by the amplifying unit becomes large, so that more power is consumed. This is shown in FIG. 2 described later.

  For example, when the output signal amplitude is changed from 100 mV to 200 mV, charging / discharging for 100 mV increases with respect to the signal line. Further, when the waveform rise times are the same, it is necessary to improve the slew rate of the amplification means.

  For this purpose, it is necessary to increase the charge / discharge capability of the signal of the amplification means. Generally, if the charge / discharge capability is increased by the amplification means having the same configuration, it is necessary to increase the current consumption. Therefore, if signal amplification is performed on the side closer to the photoelectric conversion element, the signal amplitude handled by the circuit after signal amplification is increased and power consumption is increased. Therefore, if signal amplification is performed on the side far from the photoelectric conversion element, power consumption is increased. With an excellent configuration.

  Furthermore, since the analog signal is not amplified as much as possible and is amplified by the digital signal, the amplification can be performed by a simple digital process such as a bit shift, so that the power consumption can be reduced. However, in terms of image quality, it is inevitable that the digital amplification is deteriorated as much as noise in the middle is amplified as compared with the analog amplification.

  As explained above, in terms of power consumption, since digital amplification can amplify signals with less power consumption than analog amplification, it is better to reduce amplification by analog amplification means as much as possible. Then, it is better to amplify the signal as much as possible by the analog amplification means which is the previous stage in the imaging apparatus.

  By the way, in recent digital cameras and the like, a finder often uses an electronic finder as well as an optical finder. Generally, the electronic viewfinder is called live view. Even during live view other than when the user shoots, the imaging device does not perform recording, and it is necessary to acquire images, so there is a problem that power is consumed even during live view. .

  An object of the present invention is to provide an imaging apparatus capable of reducing power consumption at the time of live view without reducing the image quality of a main image at the time of shooting, and a control method therefor.

In order to achieve the above object, an imaging apparatus according to the present invention includes a photoelectric conversion unit that converts an optical image of a subject into an electrical signal, a first amplification unit that amplifies the electrical signal output from the photoelectric conversion unit, and A second amplifying means for amplifying the electric signal amplified by the first amplifying means; an image processing means for generating image data from the electric signal output from the second amplifying means; and recording the image data. recording means for recording on the medium, a first mode for recording the more the image data in the recording means to the recording medium, the second mode of not more recording the image data on the recording medium in the recording means a mode setting means for setting one of the modes, when the first mode is set by said mode setting means sets a first amplification factor to the first amplifying means, said mode When the second mode is set by the constant unit, said by changing the power supply voltage of the first amplifying means, the first amplifying unit to the first small have second than the amplification factor An amplification factor control means for setting the amplification factor is provided .

An image pickup apparatus control method according to the present invention includes a photoelectric conversion step of converting an optical image of a subject into an electric signal by a photoelectric conversion unit, and a first amplification unit that amplifies the electric signal output in the photoelectric conversion step . Amplifying step, a second amplifying step for amplifying the electric signal amplified in the first amplifying step by a second amplifying unit, and generating image data from the electric signal output in the second amplifying step an image processing step of, and recording the image data on a recording medium, wherein a first mode for recording the image data in the recording step on the recording medium, said recording step in the image data to the recording medium a mode setting step for setting one of the modes of the second mode is not recorded, in the case where the first mode is set by said mode setting step, before The first amplification factor is set to the first amplifying unit, when the second mode is set by said mode setting step, by changing the power supply voltage of the first amplifying portion, the first further comprising a gain control step of setting the first gain small has a second amplification factor than to the amplifier and said.

According to the present invention, it is possible to reduce power consumption during live view without reducing the image quality of the main image during shooting.

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

  FIG. 1 is a diagram showing a first embodiment of a gain block in the imaging apparatus of the present invention.

  In FIG. 1, the gain block includes an image sensor 101, an AFE (analog front end) 102, and a digital signal processing circuit 103.

  The image sensor 101 includes analog amplification means 104 and a photoelectric conversion element 111. A signal generated in the photoelectric conversion element 111 is amplified in the imaging apparatus.

  The AFE 102 includes an analog amplifying unit 105, an A / D converter 106, and a digital amplifying unit 107 inside. The digital signal processing circuit 103 includes a digital amplification unit 108 and an image processing unit 109.

  FIG. 2 is a diagram illustrating distribution of amplification factors in each gain block of FIG.

  In FIG. 2, the vertical axis represents the amplification factor. FIG. 2A shows a mode for recording a photographed image (first mode), so-called gain distribution during normal photography, and FIG. 2B shows a mode for not recording a photographed signal (second mode). ) Gain distribution. As a mode not to record, there is generally a method of using live view with a digital camera.

  Here, the numbers represent the units in FIG. 1 to which the numbers are attached. In addition, a first amplification factor 201, a second amplification factor 202, a third amplification factor 203, and a fourth amplification factor 204 corresponding to the claims are shown.

  In FIG. 2, as an example, a state when a gain setting of 32 times is performed in the imaging apparatus is shown. In the recording mode of FIG. 2A, the gain distribution is increased in order from the previous stage of the amplifier circuit in the imaging apparatus. Here, the gain of the analog amplification means 104 is 8 times, the gain of the analog amplification means 105 is 4 times, the gain of the digital amplification means 107 is 1 time, and the gain of the digital amplification means 108 is 1 time.

  In the non-recording mode of FIG. 2B, the gain distribution is increased in order from the subsequent stage of the amplifier circuit in the imaging device. Here, the gain of the analog amplification means 104 is 1 time, the gain of the analog amplification means 105 is 1 time, the gain of the digital amplification means 107 is 2 times, and the gain of the digital amplification means 108 is 16 times. Here, since both the digital amplifying means 107 and the digital amplifying means 108 are digital gains, either gain distribution may be large.

  The gain of 1 described in FIG. 2 means the basic gain that can be set with respect to the gain of the analog amplifying means 104 and the analog amplifying means 105 that are analog gains, and represents the amplification factor of the signal amplitude. Not.

  For example, assuming that a settable basic gain that amplifies a signal amplitude of 100 mV to 200 mV is set to a minimum, the basic gain that is amplified to 200 mV is referred to as 1 time, and a gain that is set to 400 mV is defined as 2 times.

  As for the digital gain, outputting 100 LSB of digital data as 100 LSB is set to 1 time, and setting to 200 LSB is set to 2 times. Further, in FIG. 1 and FIG. 2, the amplifying means whose gain is not variable saves labor.

  By making the total gain of the recording mode (a) and the non-recording mode (b) the same, that is, the product of the gains, the brightness of the image in the non-recording mode and the brightness of the image in the recording mode can be improved. It becomes equivalent.

  A mode for recording from the viewpoint of noise and a mode for not recording are compared. The amount of noise generated before the analog amplifying unit 104 is α, the noise generated from the analog amplifying unit 104 to the analog amplifying unit 105 is β, and the noise generated from 105 to 107 is γ.

  At this time, in the recording mode, α is multiplied by 8 by the analog amplifying means 104, quadrupled by the analog amplifying means 105, β is quadrupled by the analog amplifying means 105, and γ is 1 times. As a result, the sum of the noise amounts is 32α + 4β + γ.

  On the other hand, in the non-recording mode, α, β, and γ are both doubled by the digital amplifying means 107 and 16 times by the digital amplifying means 108, so that the sum of the noise amounts is 32α + 32β + 32γ. In this case, the mode for recording only 16β + 31γ, which is the difference between the two, is superior to noise.

  As described above, by increasing the gain distribution from the side closer to the photoelectric conversion element 111, it is possible to perform recording with good image quality without amplifying noise generated in the subsequent stage of the amplifying means. The gain distribution is increased from the side closer to the photoelectric conversion element 111.

  It is desirable to increase the gain distribution from the side closer to the photoelectric conversion element 111 as much as possible. However, when the amplification factor of the amplifier far from the photoelectric conversion element 111 is increased, characteristics such as noise resistance become poor. May be appropriately distributed so that the noise is minimized.

  On the other hand, if a gain is applied in the analog amplification stage, the handled signal amplitude increases and the power consumption increases.

  FIG. 3 is a diagram showing a signal waveform of the output of the analog amplifying means 104 in FIG. 1 at the time of gain distribution shown in FIG.

  In FIG. 3, a signal amplitude 301 in the recording mode indicates a signal amplitude 302 in the non-recording mode. Here, the signal amplitude 302 is １ ／ times as large as the signal amplitude 301. Therefore, since the handling signal amplitude is small in the non-recording mode, the power supply voltage can be lowered.

  Further, since the signal amplitude 302 has a small output amplitude, the signal output period 303 can be secured with respect to the signal amplitude 301 even if the slew rate is lowered as shown by the broken line in FIG. Therefore, in order to reduce the slew rate, it is possible to limit the current flowing through the amplifier and suppress power consumption.

  FIG. 4 is a configuration diagram of a basic differential amplifier applied to the amplification means in FIG.

  Lowering the aforementioned power supply voltage means lowering the voltage of VDD. Current limiting is possible by limiting the current value of the constant current source 401. Accordingly, power consumption can be suppressed.

  FIG. 5 is a diagram showing a second embodiment of the gain block in the imaging apparatus of the present invention.

  2 is a diagram illustrating a gain block of an image pickup apparatus of a type in which the functions of the image pickup element 101 and the AFE 102 in FIG. 1 are the same chip and having an A / D converter 503 for each column of the image pickup elements 501. FIG. is there.

  The image sensor 501 includes an analog amplification unit 502, an A / D converter 503, and a digital amplification unit 504.

  In the imaging apparatus having the configuration as shown in FIG. 5, similarly to the configuration shown in FIG. 1, in the non-recording mode, the amplification factor is increased from the side far from the photoelectric conversion element, and in the recording mode, the amplification factor is from the side near the photoelectric conversion element. Can be increased.

  FIG. 6 is a block configuration diagram of a digital camera as the imaging apparatus according to the embodiment of the present invention.

  Hereinafter, the configuration will be described together with the operation.

  In FIG. 6, a lens unit 601 forms an optical image of a subject on an image sensor 605 (corresponding to the image sensor 101 in FIG. 1 and the image sensor 501 in FIG. 5). The lens driving device 602 performs zoom control, focus control, aperture control, and the like.

  The mechanical shutter 603 is controlled by a shutter control unit 604. The image sensor 605 takes in the subject imaged by the lens unit 601 as an image signal. The imaging signal processing circuit 606 performs amplification and A / D conversion of the image signal output from the imaging element 605. In addition, various corrections are performed on the image data after A / D conversion, and the data is further compressed.

  The timing generation circuit 607 is a driving unit that outputs various timing signals to the imaging element 605 and the imaging signal processing circuit 606. The memory unit 608 temporarily stores image data. A total control / calculation unit 609 controls various calculations and the entire imaging apparatus.

  The recording medium control I / F unit 610 is an interface for performing recording or reading on the recording medium. The removable recording medium 611 is a semiconductor memory or the like for recording or reading image data. Further, the imaging apparatus includes a display unit 612, a photometric device 613, and a distance measuring device 614.

  Next, the operation of the digital camera at the time of shooting in the above configuration will be described.

  When the main power supply is turned on, the power supply for the control system is turned on, and further, the power supply for the imaging system circuit such as the imaging signal processing circuit 606 is turned on.

  Thereafter, when the live view mode is set by a button (not shown), the image signal output from the image sensor 605 is subjected to processing such as amplification and A / D conversion in the photographing signal processing circuit 606, and the entire control / calculation unit In step S609, the image is displayed on the display unit 212 as an image.

  Further, the image signal processing circuit 606 performs an operation based on the image signal output from the image sensor 605, extracts a high-frequency component, and performs an operation of the distance to the subject by the overall control / calculation unit 609. When it is determined that the in-focus state is not achieved, the lens unit 601 is driven by the lens driving device 602. These operations may be performed based on a signal output from the distance measuring device 614.

  In the live view mode, as described above, the amplification factor of the amplifier far from the photoelectric conversion element 111 is large, and the amplification factor of the amplifier near the photoelectric conversion element 111 is small.

  Next, when a release button (not shown) is pressed, the recording mode is set. In the recording mode, a high frequency component is extracted based on the signal output from the distance measuring device 614, and the distance to the subject is calculated by the overall control / calculation unit 609.

  Thereafter, the lens driving device 602 drives the lens unit 601 to determine whether or not it is in focus. When it is determined that it is not in focus, the lens unit 601 is driven again to perform distance measurement. Then, after the in-focus state is confirmed, the photographing operation starts.

  When the photographing operation is completed, the image signal output from the image sensor 605 is subjected to processing such as amplification and A / D conversion by the photographing signal processing circuit 606, and is written to the memory unit 608 by the overall control / arithmetic unit 609.

  Thereafter, the data stored in the memory unit 608 is recorded on a removable recording medium 611 such as a semiconductor memory through the recording medium control I / F unit 610 under the control of the overall control / arithmetic unit 609.

  In the recording mode, as described above, the amplification factor of the amplifier far from the photoelectric conversion element 111 is small, and the amplification factor of the amplifier near the photoelectric conversion element is large.

  An image pickup apparatus according to the present invention includes a photoelectric conversion unit that converts an optical signal obtained from the outside into an electrical signal, a first amplification unit that amplifies a first signal obtained by the photoelectric conversion unit, and a first amplification unit. And a second amplifying means for amplifying the second signal amplified by. In addition, the image forming apparatus includes a recording unit that records an image corresponding to the optical signal, and further includes a first mode in which an image is recorded in the recording unit and a second mode in which no image is recorded in the recording unit. The first amplification means has a first amplification factor in the first mode and a second amplification factor in the second mode, and the amplification factor of 2 is greater than the first amplification factor. It is set small.

  Here, the second amplification means has a third amplification factor in the first mode and a fourth amplification factor in the second mode, and the fourth amplification factor is the third amplification factor. It is set larger.

  Further, the power supply voltage of the first amplifying means in the second mode is changed.

  Further, the current value of the first amplifying means in the second mode is changed.

  In addition, the product of the first amplification factor and the second amplification factor matches the product of the third amplification factor and the fourth amplification factor.

It is a figure which shows 1st Embodiment of the gain block in the imaging device of invention. It is a figure which shows distribution of the amplification factor in each gain block of FIG. It is a figure which shows the signal waveform of the output of the analog amplification means 104 in FIG. 1 in the case of gain distribution shown in FIG. It is a block diagram of the basic differential amplifier applied to the amplification means in FIG. It is a figure which shows 2nd Embodiment of the gain block in the imaging device of this invention. 1 is a block configuration diagram of a digital camera as an imaging apparatus according to an embodiment of the present invention.

Explanation of symbols

101 Image sensor (photoelectric conversion means)
104 Analog amplification means (first amplification means)
108 Digital amplification means (second amplification means)
201 First gain 202 Second gain 203 Third gain 204 Fourth gain

Claims (5)

Photoelectric conversion means for converting an optical image of a subject into an electrical signal;
First amplification means for amplifying an electrical signal output from the photoelectric conversion means;
Second amplification means for amplifying the electrical signal amplified by the first amplification means;
Image processing means for generating image data from an electrical signal output from the second amplification means;
Recording means for recording the image data on a recording medium ;
Mode for setting more a first mode for recording the image data on the recording medium, any of the modes of the second mode of not more recording the image data on the recording medium in the recording means to said recording means Setting means ;
When the first mode is set by the mode setting means , a first amplification factor is set in the first amplification means , and when the second mode is set by the mode setting means, wherein by changing the power supply voltage of the first amplifying means, characterized in that it comprises an amplification factor control means for setting the second gain has smaller than the first amplification factor to the first amplification means An imaging device. When the first mode is set by the mode setting means, the gain control means sets a third gain in the second amplification means, and the mode setting means sets the second mode. The imaging apparatus according to claim 1 , wherein a fourth amplification factor that is larger than the third amplification factor is set in the second amplification unit . Further, according to claim 1 or 2, characterized in that comprises an A / D converting means for converting the electrical signal amplified by the first amplifying means into a digital signal, the second amplifying means is a digital amplification means The imaging device described in 1. Furthermore, a display control means for displaying an image according to the image data on a display unit,
4. The imaging apparatus according to claim 1, wherein the display control unit displays a subject image obtained as a result of photographing on the display unit in the second mode . 5. A photoelectric conversion step of converting an optical image of a subject into an electrical signal by a photoelectric conversion unit ;
A first amplification step of amplifying the electrical signal output in the photoelectric conversion step by a first amplification unit ;
A second amplification step for amplifying the electric signal amplified in the first amplification step by a second amplification unit ;
An image processing step of generating image data from the electrical signal output in the second amplification step;
A recording step of recording the image data on a recording medium ;
First mode and a mode setting step for setting one of the modes of the second mode without recording the image data on the recording medium at the recording step of recording the image data on the recording medium at the recording step And
When the first mode is set in the mode setting step, a first amplification factor is set in the first amplification unit, and when the second mode is set in the mode setting step, and characterized in that it comprises a first by changing the power supply voltage of the amplifier, the amplification factor control step of setting the second gain has smaller than the first amplification factor to the first amplification unit Control method for imaging apparatus.

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