JP5159387B2 - Imaging apparatus and imaging element driving method - Google Patents

Description

  The present invention relates to an imaging apparatus and an imaging element driving method, and more particularly to an imaging apparatus and an imaging element driving method capable of performing smear correction.

  A typical example of a solid-state imaging device used in an imaging apparatus such as a digital camera or a video camcorder is a CCD (Charge Coupled Device). In one type of interline transfer type CCD, charges accumulated in each pixel as a light receiving section pass through each vertical CCD (vertical transfer path) from each pixel and are transferred to a horizontal CCD (horizontal transfer path). The FIG. 5 shows a schematic configuration of an interline transfer type CCD.

  The CCD 401 is connected to a plurality of light receiving portions (pixels) 402, a vertical CCD 403 to which the plurality of light receiving portions 402 are connected, one horizontal CCD 404 to which one end of the plurality of vertical CCDs 403 is connected, and the horizontal CCD 404. A charge detection unit 405. The output buffer 406 is connected to the charge detection unit 405. These are integrally formed on, for example, an N-type semiconductor substrate (not shown).

  The CCD 401 includes a plurality of light receiving units 402 that are arranged in a matrix and photoelectrically convert received light into signal charges having a charge amount corresponding to the light amount. The light receiving unit 402 is made of, for example, a photodiode. The CCD 401 includes a vertical CCD 403 that transfers signal charges read from the light receiving unit 402 in the vertical direction (vertical direction in the drawing) for each vertical pixel column with respect to the arrangement of the plurality of light receiving units 402.

  The signal charges read from each of the light receiving units 402 are transferred to the horizontal CCD 404 via the vertical CCD 403, and then transferred to the charge detection unit 405, where the charge detection unit 405 performs charge voltage conversion, and the signal is converted into a voltage. Read out.

  When the CCD 401 is irradiated with high-luminance light such as spotlight or sunlight, part of the signal charge passes through the vertical CCD 403 where the spot light is applied. At this time, the light leaked into the vertical CCD 403 or the charge generated by the charge leak from each light receiving unit is mixed. As a result, as shown in FIG. 6, in the output image (recording / display image during moving image) 501 of the CCD 401, white or magenta bands 503 are generated above and below the image so as to penetrate the spot light 502. This is called smear. The principle of smear generation will be described with reference to FIGS. 7 (a) to 7 (c).

  The incident light to the image pickup device normally passes through the lens, and then is condensed by the microlens 603 provided on the upper part of each light receiving unit 604 of the CCD 401, and as shown in FIG. It enters the part 604.

  A principal ray 601 represents a principal ray of light incident on the microlens 603. A peripheral ray 602 is a peripheral ray of light that passes through the microlens 603 provided on the top of each light receiving unit 604 of the CCD 401 and is incident on each light receiving unit 604. In the case shown in FIG. 7A, the incident angle of the principal ray 601 is substantially perpendicular to the light receiving surface of the light receiving unit 604 near the center of the CCD 401. On the other hand, in the peripheral part, as shown in FIG. 7B, it is often incident obliquely at an angle according to the characteristics of the lens. Under such conditions, light leaks easily into the vertical CCD 403 described above, and smear characteristics deteriorate. As described above, it is known that the smear depends on the incident angle of light to the light receiving unit.

  A CCD generally has a left-right asymmetric structure with a light receiving portion interposed therebetween. Specifically, as shown in the figure, a channel stop 607 is formed at one end (left side in the figure) of the light receiving unit 604, and a read gate 608 wider than the channel stop 607 is formed at the other end (right side in the figure). Is formed. Due to this left-right asymmetric structure, as shown in FIGS. 7B and 7C, when the incident angle of light to the light receiving unit 604 is reversed, light and charges leak into the vertical CCD. Ease is different and the way smears appear is different. As a result, the smear is not uniform in the image. Therefore, an imaging apparatus capable of calculating a smear included in the output from the image sensor and further performing smear correction when a moving image is recorded using the imaging apparatus or when a moving image or a still image is displayed by EVF. Proposed.

  In recent years, with the narrowing of CCD pixels, the allowable range for the angle of light passing through the lens has decreased, and the imaging device itself tends to be light and thin, making the optical system compact and making the light incident on the CCD surface. The corners are also tight and the smear characteristics tend to deteriorate. For this reason, smearing occurs even from subjects with brightness that did not generate smear in the past, such as blue sky, clouds, and white walls where the signal level of the pixel is not saturated, and the blue sky and white walls become magenta. Is greatly deteriorated.

  Further, when a high-luminance object moves within the display screen of the display device, the smear may also move within the screen and tilt or become a curved line. There are the following methods for removing the smear component.

  A pixel signal is read out as an imaging output of one field via a horizontal register of a CCD image sensor capable of simultaneous readout of two lines, and only a smear component is read out as an imaging output of the other field via the other horizontal register. There is a method of removing smear components by subtracting and synthesizing the imaging output of each field with a subtractor (see, for example, Patent Document 1).

  In addition, a current mirror circuit for flowing a charge corresponding to the signal charge including a smear component into the floating diffusion region and a current mirror circuit for sucking a charge corresponding to the unnecessary charge as a smear component from the floating diffusion region are provided. Then, there is a method of subtracting the smear component from the signal charge including the smear component in the floating diffusion region by switching each operation of the current mirror circuit in synchronization with the transfer operation of the horizontal CCD (see, for example, Patent Document 2). ).

Further, there is a method in which information charges are discharged by a reset clock φr1 having a period twice that of the horizontal clock φh by the output unit of the image sensor to synthesize information charges two pixels at a time (see, for example, Patent Document 3). ). In Patent Document 3, the image signal Y0 (t) output from the output unit is captured in two stages, and a period representing the information charge amount for one pixel and a period representing the information charge amount for two pixels are alternately repeated. A sample hold circuit that outputs an image signal Y1 (t) is disclosed.
Japanese Patent Laid-Open No. 06-339077 JP 2005-101791 A Japanese Patent Laid-Open No. 10-229521

  However, the technique described in Patent Document 1 requires a horizontal register for transferring imaging charges for odd-numbered field lines and a horizontal register for transferring imaging charges for even-numbered field lines, so that the structure of the solid-state imaging device is complicated. become. As a result, there is a problem that the yield of the apparatus is reduced and the cost is increased.

  In the technique described in Patent Document 2, as shown in FIG. 8, a period of two fields in total is required to obtain data excluding smear components, and the frame rate may be significantly reduced.

  In the technique described in Patent Document 3, since the image signal Y0 (t) is captured in two stages, a plurality of clocks are required, and the structure of the solid-state imaging device is complicated. As a result, there is a problem that the yield of the apparatus is reduced and the cost is increased.

  The present invention has been made in view of the above problems, and can reduce deterioration in image quality due to smear while reducing a decrease in frame rate due to smear correction during moving image shooting without adding a complicated circuit. An object of the present invention is to provide an imaging apparatus and a driving method of an imaging element.

In order to achieve the above object, an imaging apparatus of the present invention includes a plurality of light receiving units arranged in a matrix and having a photoelectric conversion function, and a plurality of vertical transfers arranged along each column of the plurality of light receiving units. And a horizontal transfer path formed at one end of the plurality of vertical transfer paths, and at the time of shooting, only signal charges generated by a predetermined part of the plurality of light receiving parts are used for the imaging. An image sensor that transfers to a vertical transfer path and outputs a pixel signal including a signal charge and a smear component of the light receiving unit and a smear signal including only a smear component via the horizontal transfer path, and is output from the image sensor The smear signal and a charge detection unit that reads the pixel signal, and the charge detection unit resets the charge and immediately after reading the pixel signal, without resetting the charge of the charge detection unit, Previous Wherein the read out signal including the smear signal and the pixel signal.

In order to achieve the above object, an image sensor driving method according to the present invention includes a plurality of light receiving units arranged in a matrix and having a photoelectric conversion function, and a plurality of light receiving units arranged along each column of the plurality of light receiving units. And a horizontal transfer path formed at one end of the plurality of vertical transfer paths, and a signal charge generated by a predetermined part of the plurality of light receiving parts during photographing. Image signal is transferred to the vertical transfer path, and a pixel signal including a signal charge and a smear component of the light receiving unit and a smear signal including only a smear component are output via the horizontal transfer path. When the smear signal and the pixel signal output from the image sensor are read by the charge detection unit, the charge of the charge detection unit is read immediately after resetting the charge of the charge detection unit and reading the pixel signal. The Without Tsu bets, characterized in that reading out the signal containing the pixel signal and the smear signal.

  According to the present invention, it is possible to reduce deterioration in image quality due to smear while reducing a decrease in frame rate due to smear correction during moving image shooting without adding a complicated circuit.

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

[First Embodiment]
FIG. 1 is a block diagram showing a schematic configuration of an imaging apparatus according to the first embodiment of the present invention.

  In FIG. 1, an optical system 301 is a lens group composed of lenses and the like for forming a subject image on an image plane. A diaphragm 302 is a diaphragm for controlling the amount of image plane light from the optical system 301. The mechanical shutter 303 is a mechanical shutter for controlling the time when light enters from the optical system 301. The imaging unit 304 is an imaging element for converting a subject image formed by the optical system 301 into an electrical signal, and for example, a CMOS area sensor is used.

  The imaging element driving circuit 305 is an imaging unit driving circuit that supplies a pulse having a necessary amplitude for driving the imaging unit 304. The CDS circuit 306 is a CDS circuit that performs double correlation sampling on the output from the imaging unit 304. The AGC circuit 307 is an AGC circuit for amplifying the output signal of the CDS circuit 306. The gain setting of the AGC circuit 307 is changed when the user changes the sensitivity setting of the imaging apparatus or when the imaging apparatus automatically increases the gain when the luminance is low.

  The CLP circuit 308 is a clamp circuit (CLP circuit) for clamping an OB (Optical Black) potential described later among the output signals of the AGC circuit 307 to a reference potential. The AD conversion circuit 309 is an AD conversion circuit that converts an analog imaging signal output from the clamp circuit 308 into a digital signal.

  The video processing circuit 310 includes a video signal processing circuit 311, a photometry circuit 312, and an OB integration circuit 317. Although not shown, the video processing circuit 310 measures the color temperature of the subject based on the signal input from the imaging unit 304 and obtains information necessary for white balance processing in the video signal processing circuit 311. A circuit such as a circuit is provided.

  The video signal processing circuit 311 converts the imaging signal converted into the digital signal into a video signal of luminance and color (R-Y, BY color difference signals, or R, G, B signals). The photometric circuit 312 measures the photometric quantity from the level of the signal input from the imaging unit 304. The timing generator 313 is a timing pulse generation circuit (TG) that generates timing pulses necessary for circuits in each unit in the imaging apparatus.

  The CPU 314 controls each unit in the imaging apparatus. The CPU 314 includes a sensitivity / exposure control unit 315 and an OB level block comparison circuit 318. The OB level block comparison circuit 318 compares the signal level obtained by the OB integration circuit 317 with a preset black level, and outputs the result to the sensitivity / exposure control unit 315. The sensitivity / exposure control unit 315 outputs a command for changing the gain to the AGC circuit 307 in order to control sensitivity and exposure based on information from the photometry circuit 312 and the OB level block comparison circuit 318. The sensitivity / exposure control unit 315 has a function of issuing an exposure control command to the exposure control circuit 316. The switch 319 is a switch for instructing a moving image shooting operation by a user operation.

  FIG. 2 is a diagram illustrating a schematic structure of an imaging unit in the imaging apparatus of FIG.

  In FIG. 2, the imaging unit 101 corresponds to the imaging unit 304 of FIG. The imaging unit 101 is connected to a plurality of light receiving units (pixels) 102, a vertical CCD 103 connected to the plurality of light receiving units 102, one horizontal CCD 104 connected to one end of the plurality of vertical CCDs 103, and the horizontal CCD 104. The charge detection unit 105 is provided. An output buffer 106 is connected to the charge detection unit 105. These are integrally formed on, for example, an N-type semiconductor substrate (not shown).

  The imaging unit 101 includes a plurality of light receiving units (pixels) 102 that are arranged in a matrix and have a photoelectric conversion function of converting received light into signal charges having a charge amount corresponding to the amount of light. The light receiving unit 102 is made of, for example, a photodiode. In addition, the imaging unit 101 includes a vertical CCD 103 that transfers the signal charge generated by the light receiving unit 102 in the vertical direction (vertical direction in the drawing) for each vertical pixel column with respect to the arrangement of the plurality of light receiving units 102. The vertical CCD 103 has a packet (one transfer stage) twice the number of pixels in the vertical direction at least in a portion corresponding to the light receiving unit 102.

  In the present embodiment, signal charges generated by each light receiving unit 102 are stored in every other packet (hereinafter referred to as “pixel signal”), and this pixel signal and a smear component only signal (hereinafter referred to as “smear signal”). The vertical transfer is performed in a state where the signals are alternately arranged. This is called a vertical transfer electrode.

  Assuming that smear is generated in the vertical CCD 103 for the above-described reason, signal charges and smear components are included in the pixel signal of the vertical CCD 103. On the other hand, in the smear signal, only the smear component exists as unnecessary charges. The vertical transfer electrode may be configured to perform vertical pixel addition for adding the charges of a plurality of vertically arranged pixels, or thinning transfer for reading an arbitrary pixel from the plurality of vertically arranged pixels. Also in this case, the smear signal containing only the smear component and the pixel signal containing the signal charge and the smear component are alternately arranged.

  Signal charges transferred by each of the vertical CCDs 103 are transferred from the imaging unit 101 to the horizontal CCD 104 in units of rows (lines). The horizontal CCD 104 can transfer a signal at least twice the number of pixels in the horizontal direction to at least a portion corresponding to the light receiving unit 102. When the smear signal of the light receiving pixels is transferred from the vertical CCD 103 to every other packet for every other row to the horizontal CCD 104, it is shifted by one transfer stage (one packet), and then the pixel signal is shifted to the vertical CCD 103. Is transferred to the remaining packets every other line.

  The horizontal CCD 104 sequentially transfers pixel signals (● (black circles) in the figure) and smear signals (◯ (white circles) in the figure) transferred from the imaging unit 101 in the horizontal direction in order. Sequentially supplied to the charge detector 105 provided at the end on the front side. The output from the charge detection unit 105 is a characteristic feature of the present invention, and details of its specific operation will be described later. The output buffer 106 converts the signal charge (signal current) detected by the charge detection unit 105 into a signal voltage and outputs the signal voltage.

  FIG. 3 is a diagram illustrating an example of an output signal waveform of the charge detection unit 105 in FIG.

  The output signal detected by the charge detection unit 105 has a waveform as shown in FIG. The vertical axis represents the signal output of the charge detection unit 105, and the horizontal axis represents time.

  In FIG. 3, the charge detection unit 105 in the present embodiment outputs a signal while repeating a reset period, a feedthrough period, a smear signal readout period, a smear signal + pixel signal readout period, and a reset period. Thus, in the charge detection unit 105, immediately after the charge is reset and the smear signal is read out, the signal including the pixel signal and the smear signal is read out without further resetting the charge. As shown in FIG. 8, the conventional charge detection unit outputs signals while repeating the reset period, feedthrough period, smear signal readout period, reset period, feedthrough period, and pixel signal readout period. .

  The charge detection unit 105 is reset by discharging the charge during the reset period. Next, the reset voltage Vreset is acquired during the feedthrough period after the reset period. The voltage Vreset is output from the imaging unit 304 and input to the CDS circuit 306.

  Next, an empty packet enters the charge detection unit 105 via the horizontal CCD (horizontal transfer path) 104, and the voltage Vs1 at that time is acquired. The voltage Vs1 is output from the imaging unit 304 and input to the CDS circuit 306.

  From the above, the signal amount Vsmear1 of the smear signal is expressed by the following equation.

Vsmear1 = Vs1-Vreset
Further, the pixel signal enters the charge detection unit 105 from the horizontal CCD (horizontal transfer path) 104, and the voltage Vg1 at that time is acquired. The voltage Vg1 is output from the imaging unit 304 and input to the CDS circuit 306.

  As described above, the voltage Vsignal corresponding to the signal charge generated by the light receiving unit 102 excluding the smear component can be obtained by the following equation.

Vsignal = Vg1-Vsmear1-Vreset
= Vg1-Vs1
According to the first embodiment, the charge detection unit 105 is reset only once when reading a pair of smear signal and pixel signal, compared with the case where the conventional current mirror circuit is used, and the frame rate is reduced. Reduction can be reduced. Further, since it is not necessary to provide two horizontal CCDs (horizontal transfer paths) 104, it is not necessary to add a complicated circuit.

  As described above, in the imaging unit 304, the pixel signals and the smear signals are arranged in a horizontal row on the vertical CCD 103 from the plurality of light receiving units 102 arranged in a matrix and having a photoelectric conversion function in the vertical direction. Are read out. Then, the smear signal for one row and the pixel signal for one row are transferred via the vertical CCD 103 so as to be alternately arranged on the horizontal transfer path. Furthermore, a set of smear signals and pixel signals are continuously read out without resetting the charge of the charge detection unit 105. As a result, it is possible to perform smear correction while reducing a decrease in the frame rate during moving image shooting for recording and display frames without adding a complicated circuit.

[Second Embodiment]
The imaging apparatus according to the second embodiment of the present invention has the same configuration (FIG. 1) as that of the imaging apparatus according to the first embodiment, and the same parts as those in the first embodiment. The description will be omitted using the same reference numerals. Only differences from the first embodiment will be described below.

  In the first embodiment described above, a configuration has been described in which empty packets are read first and pixel signals are read later. In this case, if the signal value exceeds the saturation amount when reading out the pixel signal, a smear component is excessively subtracted from the saturated pixel signal, and overcorrection occurs. Therefore, a method of reading the pixel signal first after the reset period and then reading the empty packet will be described.

  FIG. 4 is a diagram illustrating an example of an output signal waveform of the charge detection unit 105 of the imaging unit in the second embodiment of the present invention.

  The output signal detected by the charge detection unit 105 has a waveform as shown in FIG. The vertical axis represents the signal output of the charge detection unit 105, and the horizontal axis represents time.

  In FIG. 4, the charge detection unit 105 in the present embodiment performs signal output while repeating a reset period, a feed-through period, a pixel signal readout period, a smear signal + pixel signal readout period, and a reset period. In this way, in the charge detection unit 105, immediately after the charge is reset and the pixel signal is read, the signal including the pixel signal and the smear signal is read without resetting the charge.

  As in the first embodiment, the charge detection unit 105 is reset by discharging charges during the reset period. Next, the reset voltage Vreset is acquired during the feedthrough period after the reset period. The voltage Vreset is output from the imaging unit 304 and input to the CDS circuit 306.

  Next, the pixel signal enters the charge detection unit 105 via the horizontal CCD (horizontal transfer path) 104, and the voltage Vg2 at that time is acquired. Further, an empty packet enters the charge detection unit 105 via the horizontal CCD (horizontal transfer path) 104, and the voltage Vs2 at that time is acquired.

  From the above, the signal amount Vsmear2 of the smear signal is expressed by the following equation.

Vsmear2 = Vs2-Vg2
As described above, the voltage Vsignal corresponding to the signal charge generated by the light receiving unit 102 excluding the smear component can be obtained by the following equation.

Vsignal = Vg2-Vsmear2-Vreset
= Vg2 × 2-Vs2-Vreset
According to the above equation, when the pixel signal is saturated, Vs2 = Vg2, so Vsmear = 0 and smear overcorrection is not performed. Further, by reading out the pixel signal first, similarly to the first embodiment, the dynamic range is not narrowed by the amount of the smear signal read out first.

  According to the second embodiment, in addition to the effects in the first embodiment, by defining the signal reading order, not only simple reading time reduction but also smear correction such as overcorrection and narrowing the dynamic range. The adverse effects of time can be eliminated. In addition, it is not necessary to mount a circuit for preventing overcorrection, which has been conventionally required, and the circuit configuration can be greatly simplified.

  As described above, according to the present invention, it is possible to reduce smear correction without worrying about over-correction while reducing a decrease in the frame rate during movie recording for recording and display frames without adding a complicated circuit. Can be done.

  Note that the software configuration and hardware configuration described in the first and second embodiments are not limited to the described components, and can be replaced as appropriate. Moreover, even if it combines said each embodiment or those technical elements as needed, this invention can be implement | achieved and the effect similar to the effect mentioned above can be acquired.

  Further, in the present invention, the configuration of the claims or the whole or a part of the configuration of the embodiment may form one apparatus. And even if it is combined with other devices, such as an imaging device such as a digital camera or a video camera, or a signal processing device that processes a signal obtained from the imaging device, it becomes a component of the device It may be.

1 is a block diagram illustrating a schematic configuration of an imaging apparatus according to a first embodiment of the present invention. It is a figure which shows schematic structure of the imaging part in the imaging device of FIG. It is a figure which shows an example of the output signal waveform of the electric charge detection part in FIG. It is a figure which shows an example of the output signal waveform of the electric charge detection part of the imaging part in the 2nd Embodiment of this invention. It is a figure which shows schematic structure of a general CCD. It is a figure which shows an example of the generated smear. It is a figure which shows an example of the light which injects into the light-receiving part in CCD, (a) is a case where incident light injects substantially perpendicular | vertical with respect to the light-receiving surface of a light-receiving part, (b) is an incident light with respect to a light-receiving surface (C) shows the case where the incident direction of the light in (b) is reversed. It is a figure which shows an example of the output signal of the electric charge detection part in the conventional smear detection method.

Explanation of symbols

101 Imaging unit 102 Light receiving unit 103 Vertical CCD
104 Horizontal CCD
105 Charge Detection Unit 106 Output Buffer 300 Imaging Unit 301 Lens 303 Mechanical Shutter

Claims (6)

A plurality of light receiving portions arranged in a matrix and having a photoelectric conversion function, a plurality of vertical transfer paths arranged along each column of the plurality of light receiving portions, and formed at one end of the plurality of vertical transfer paths A horizontal transfer path, and at the time of shooting, only the signal charges generated by a predetermined part of the plurality of light receiving units are transferred to the vertical transfer path, through the horizontal transfer path, An image sensor that outputs a pixel signal including a signal charge and a smear component of the light receiving unit and a smear signal including only a smear component, and a charge detector that reads the smear signal and the pixel signal output from the image sensor. Prepared ,
The charge detection unit reads the signal including the pixel signal and the smear signal immediately after resetting the charge and reading the pixel signal without resetting the charge of the charge detection unit. Imaging device. Wherein the vertical transfer path, the portion corresponding to at least the light receiving section, an imaging apparatus according to claim 1, characterized in that it has twice the packet number of pixels in the vertical direction. The charge detection unit reads the signal including the pixel signal and the smear signal without resetting the charge of the charge detection unit immediately after resetting the charge and reading the smear signal. The imaging device according to claim 1 or 2 . A plurality of light receiving portions arranged in a matrix and having a photoelectric conversion function, a plurality of vertical transfer paths arranged along each column of the plurality of light receiving portions, and formed at one end of the plurality of vertical transfer paths A horizontal transfer path, and at the time of shooting, only the signal charges generated by a predetermined part of the plurality of light receiving units are transferred to the vertical transfer path, through the horizontal transfer path, A driving method of an image sensor that outputs a pixel signal including a signal charge and a smear component of the light receiving unit and a smear signal including only a smear component,
When the smear signal and the pixel signal output from the image sensor are read by the charge detection unit, the charge of the charge detection unit is reset immediately after resetting the charge of the charge detection unit and reading the pixel signal. A driving method of reading out a signal including the pixel signal and the smear signal without doing so . 5. The driving method according to claim 4, wherein the vertical transfer path has a packet twice as many as the number of pixels in the vertical direction at least in a portion corresponding to the light receiving unit. The charge detection unit reads the signal including the pixel signal and the smear signal without resetting the charge of the charge detection unit immediately after resetting the charge and reading the smear signal. The driving method according to claim 4 or 5 .

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