U.S. patent application number 12/815518 was filed with the patent office on 2010-09-30 for imaging apparatus and imaging system.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Seiji Hashimoto.
Application Number | 20100245628 12/815518 |
Document ID | / |
Family ID | 38087034 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100245628 |
Kind Code |
A1 |
Hashimoto; Seiji |
September 30, 2010 |
IMAGING APPARATUS AND IMAGING SYSTEM
Abstract
An imaging apparatus includes a pixel unit having a plurality of
components, each having a plurality of pixels arranged in row and
column directions. The plurality of pixels in each component output
color signals having a plurality of colors. The apparatus also
includes an adding unit configured to perform an addition of color
signals of the same color in each component. The color signals are
outputted from the plurality of pixels. The adding unit performs
the addition without adding a color signal outputted from a part of
the plurality of pixels in each component such that spatial
centroids of the added color signals having a plurality of colors
are located at substantially the same pitch at least in one of the
row and column directions.
Inventors: |
Hashimoto; Seiji;
(Yokohama-shi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
1290 Avenue of the Americas
NEW YORK
NY
10104-3800
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
38087034 |
Appl. No.: |
12/815518 |
Filed: |
June 15, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11555438 |
Nov 1, 2006 |
7760959 |
|
|
12815518 |
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Current U.S.
Class: |
348/231.99 ;
348/272; 348/E5.091 |
Current CPC
Class: |
H04N 9/04557 20180801;
H04N 9/045 20130101; H04N 9/0451 20180801 |
Class at
Publication: |
348/231.99 ;
348/272; 348/E05.091 |
International
Class: |
H04N 5/335 20060101
H04N005/335; H04N 5/76 20060101 H04N005/76 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 4, 2005 |
JP |
2005-321398 |
Claims
1-8. (canceled)
9. An imaging apparatus comprising: a pixel unit having a plurality
of components, each having a plurality of pixels arranged in row
and column directions, the plurality of pixels in each component
outputting color signals having a plurality of colors; and an
adding unit configured to perform the addition of color signals of
the same color from an identical row within each component to
generate a horizontally added signal, and to perform an addition of
the horizontally added signals from different rows of each
component, and wherein the adding unit performs the addition
without adding a color signal output from a part of the plurality
of pixels in each component such that spatial centroids of the
added color signals having a plurality of colors are located at
substantially the same pitch at least in one of the row and column
directions.
10. The apparatus according to claim 9, wherein four pixels located
at four corners of the plurality of pixels arranged in row and
column directions in each of the components output the same color
and the adding unit adds the color signals outputted from the four
pixels.
11. The apparatus according to claim 9, wherein the adding unit
does not perform an addition of the color signals outputted from
pixels arranged at least in one of even rows and even columns of
the plurality of pixels arranged in row and column directions of
each of the components.
12. The apparatus according to claim 9, wherein the adding unit
does not perform an addition of the color signals outputted from
pixels arranged at least in one of odd rows and odd columns of the
plurality of pixels arranged in row and column directions of each
of the components.
13. The apparatus according to claim 9, wherein a part of at least
one of the plurality of components spatially overlaps a part of the
another one of the plurality of components.
14. The apparatus according to claim 9, wherein each of the
plurality of components includes 2N+1 pixels in the row and column
directions respectively, where N is an integer greater than or
equal to 1.
15. The apparatus according to claim 9, wherein each of the
plurality of components includes 2N pixels in the row and column
directions respectively, where N is an integer greater than or
equal to 1.
16. The apparatus according to claim 9, wherein each of the
plurality of pixels of each component includes an arrangement in
which a plurality of photodiodes share an amplifier.
17. An imaging system comprising: an imaging apparatus defined in
claim 9; an optical system configured to converge light to form an
image on the imaging apparatus; a recording system configured to
record an output signal from the imaging apparatus; and a system
control circuit configured to control the entire imaging system.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 11/555,438, filed Nov. 1, 2006, pending.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to an imaging
apparatus and an imaging system. In particular, the present
invention relates to capturing an object image.
[0004] 2. Description of the Related Art
[0005] In recent years, image sensors in which the number of pixels
ranges from several million to ten million or more has been
employed for digital still cameras whose primary usage is still
image recording. These cameras are used not only to capture truly
high definition still images, but also for recording of high
definition still images, high-resolution moving images, or movie
recording such as NTSC that are becoming important functions.
Although all pixel signals are utilized in truly high definition
images, for images that are high definition and below, pixel
signals to be read out are thinned out or addition of pixel signals
is performed to increase sensitivity.
[0006] Japanese Patent Application Laid-Open No. 9-247689 discloses
an arrangement of thinning and reading out the same color by adding
output signals from each pixel in units of 4.times.4 pixels.
Japanese Patent Application Laid-Open No. 2001-36920 discloses an
arrangement of adding a plurality of pixel signals employing
4.times.4 pixels as one component such that the spatial color array
of each color before addition is the same as that of each color
after addition.
[0007] Japanese Patent Application Laid-Open No. 9-046596 discloses
an arrangement comprising a common amplifier in each pixel and
performing an addition of pixels with a floating unit of the common
amplifier.
[0008] According to Japanese Patent Application Laid-Open No.
9-247689, although thinning and addition is performed, addition is
carried out using vertical signal lines and horizontal signal
lines. As a result, a large amount of kTC noise is generated by
parasitic capacitances of the signal lines, and enhancing SN is
difficult. Further, according to Japanese Patent Application
Laid-Open No. 9-247689, a plurality of pixels arranged in a matrix
are grouped in components of 4.times.4 pixel units, and among the
color signals of pixels arranged inside these components, four
signals of the same color are added.
[0009] According to the arrangement disclosed in Japanese Patent
Application Laid-Open No. 9-247689, since the optical sampling
pitches of the pixels to be added, that is, the spatial centroids,
are not substantially the same pitch in the horizontal direction
and vertical direction, an extremely large moire is created and the
image quality deteriorates significantly.
[0010] According to an arrangement disclosed in Japanese Patent
Application Laid-Open No. 2001-36920, although the number of pixel
signals added within a single component is increased to enhance
sensitivity, pixel rows are not thinned out and it is difficult to
achieve high speed driving. In a pixel amplifier-type area sensor,
driving is performed in which the pixel amplifier is reset in units
of each pixel row, noise is read out, photoelectric conversion
signals are transferred, and the photoelectric conversion signals
are read out. This driving requires several .mu. seconds of time,
and speeding up is thus not possible in sensors with a large number
of pixel rows.
[0011] According to an arrangement disclosed in Japanese Patent
Application Laid-Open No. 9-046596, a signal addition is performed
with a floating unit and thus sensitivity is enhanced. However,
similarly to Japanese Patent Application Laid-Open No. 2001-36920,
the signals of all pixels are transferred to a floating unit and
are also read from a pixel amplifier, and thus time is required for
this driving and the operation cannot be carried out at the driving
frequency of moving images.
[0012] As described above, with the prior art, even when thinning
and pixel addition is performed, moire is created since the spatial
centroids of the pixels to be added are not substantially the same
pitch. Further, there is a problem that even when addition of pixel
signals is performed with a common pixel amplifier, time is
required for pixel driving and a driving frequency of moving images
cannot be obtained.
SUMMARY OF THE INVENTION
[0013] The present invention has been made in consideration of the
above problems, and has as its object to provide an imaging
apparatus and an imaging system which reduce the formation of moire
fringes.
[0014] A first aspect of the present invention is associated with
an imaging apparatus, and is characterized by comprising a pixel
unit having a plurality of components, each having a plurality of
pixels arranged in row and column directions. The plurality of
pixels in each component output color signals having a plurality of
colors. The apparatus also comprises an adding unit configured to
perform an addition of color signals of the same color in each
component, the color signals being outputted from the plurality of
pixels. The adding unit performs the addition without adding a
color signal outputted from a part of the plurality of pixels in
each component such that spatial centroids of the added color
signals having a plurality of colors are located at substantially
the same pitch at least in one of the row and column
directions.
[0015] A second aspect of the present invention is associated with
an imaging system, and is characterized by comprising the above
imaging apparatus, an optical system configured to converge light
to form an image on the imaging apparatus, a recording system
configured to record an output signal from the imaging apparatus,
and a system control circuit configured to control the entire
system.
[0016] Further features of the present invention will be apparent
from the following description of exemplary embodiments with
reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention and, together with the description, serve to explain
the principles of the invention.
[0018] FIG. 1 is a diagram illustrating an example of an array of
respective colors before adding pixel signals;
[0019] FIG. 2 is a diagram illustrating the color array and the
addition signals after adding the pixel signals;
[0020] FIGS. 3A and 3B are views illustrating an addition method
according to the preferred first embodiment of the present
invention;
[0021] FIGS. 4A and 4B are views illustrating an addition method
according to the preferred second embodiment of the present
invention;
[0022] FIGS. 5A and 5B are views illustrating an overlapping pixel
addition method according to a preferred third embodiment of the
present invention;
[0023] FIG. 6 is a circuit block diagram of an imaging apparatus
according to a preferred embodiment of the present invention;
[0024] FIG. 7 is a circuit diagram of one part of a readout signal
processing circuit for reading out pixel signals from the imaging
area according to a preferred first embodiment of the present
invention;
[0025] FIG. 8 is a timing chart for readout and addition of pixel
signals;
[0026] FIG. 9 is a view illustrating a case using a mechanical
shutter;
[0027] FIG. 10 is a timing chart for addition of pixel signals of
FIG. 3A;
[0028] FIG. 11 is a timing chart for readout of all pixel signals
of FIG. 7;
[0029] FIG. 12 is a circuit diagram of a unit pixel of the pixel
unit;
[0030] FIG. 13 is a circuit diagram of a shared amplifier pixel;
and
[0031] FIG. 14 is a view illustrating an imaging system using the
above imaging apparatus.
DESCRIPTION OF THE EMBODIMENTS
[0032] Preferred embodiments of the present invention will now be
described in detail with reference to the drawings. It should be
noted that the relative arrangement of the components, the
numerical expressions and numerical values set forth in these
embodiments do not limit the scope of the present invention unless
it is specifically stated otherwise.
First Embodiment
[0033] FIG. 1 is a diagram illustrating an example of an array of
respective colors before adding pixel signals. Reference numeral
101 corresponds to one pixel. In a pixel unit 100, a plurality of
components that include multiple pixels are arrayed in a row
direction and a column direction. FIG. 2 is a diagram illustrating
the color array after adding pixel signals. Reference numeral 201
corresponds to one pixel after addition.
[0034] For the color array example shown in FIG. 1, it is assumed
that color filters G (Green), R (Red), and B (Blue) are configured
on each photodiode of an imaging apparatus. In this example, G is
arrayed in a checkerboard pattern, and R and B are arrayed in every
other line, in other words, in a 2.times.2 matrix, i.e., 4 pixels
of R, G, G, and B are disposed two-dimensionally as one unit of a
pixel color array.
[0035] In a pixel signal addition and readout imaging mode of this
embodiment, as shown in FIG. 2, in order to obtain the same color
array as FIG. 1, pixel signals are added within the imaging
apparatus, the result is stored in a memory, and the result is then
read out from the imaging apparatus. Thus, since the pixel array is
the same before and after addition of pixel signals, it is possible
to perform common image processing.
[0036] FIGS. 3A to 5B are views that illustrate a thinning driving
operation according to a preferred first embodiment of this
invention. In FIGS. 3A to 5B, a plurality of components having
pixels in odd rows and odd columns are arrayed. These figures
illustrate an example of pixel addition that adds color signals of
the same color within each component. In FIGS. 3A and 3B, reference
numeral 301 corresponds to a single component. In FIGS. 4A and 4B,
reference numeral 401 corresponds to a single component. FIGS. 3A
and 3B are views illustrating a case that takes nine pixels
consisting of three rows and three columns as a single component
301, in which four pixels of the same color within that component
are added. FIG. 3A is a view showing pixels to be added. In FIG.
3A, sensitivity can be enhanced by adding four pixel signals, and
the operating frequency can be increased by performing a thinning
driving operation for the pixel rows and pixel columns in the
middle (i.e. not using them as pixel signals). In this example, the
vertical driving frequency and the horizontal driving frequency can
be increased to approximately 3/2 and their driving period can be
reduced to approximately 2/3, respectively. FIG. 3B illustrates an
operational expression of the addition signals shown in FIG. 3A. In
this connection, to simplify the diagrammatic representation, the
notation of parentheses showing the coordinates is omitted in each
drawing. A pixel r(1,1) shown in FIG. 3B is a pixel obtained by
adding the pixel signals of pixels R(1,1), R(1,3), R(3,1) and
R(3,3) shown in FIG. 3A. Likewise, a pixel g(1,2) shown in FIG. 3B
is obtained by adding the pixel signals of pixels G(1,4), G(1,6),
G(3,4) and G(3,6) shown in FIG. 3A. Further, a pixel g(2,1) shown
in FIG. 3B is a pixel obtained by adding the pixel signals of
pixels G(4,1), G(4,3), G(6,1) and G(6,3) shown in FIG. 3A. Also, a
pixel b(2,2) shown in FIG. 3B is obtained by adding the pixel
signals of pixels B(4,4), B(4,6), B(6,4) and B(6,6) shown in FIG.
3A.
[0037] The spatial centroids of pixels to be added within the
components are determined as follows. Herein, the term "spatial
centroids of pixels to be added" refers to the geometric centroid
of each pixel that is an object of addition. Accordingly, for
example, the spatial centroid of pixels R(1,1), R(1,3), R(3,1) and
R(3,3) shown in FIG. 3A is (N, n)=(2, 2). Likewise, the spatial
centroid of pixels G(1,4), G(1,6), G(3,4) and G(3,6) is (N, n)=(2,
5). Also, the spatial centroid of pixels G(4,1), G(4,3), G(6,1) and
G(6,3) is (N, n)=(5, 2). Further, the spatial centroid of pixels
B(4,4), B(4,6), B(6,4), and B(6,6) is (N, n)=(5, 5). Thus, the
array pitch of the spatial centroid of each pixel to be added is
substantially the same pitch for the three pixels in the row
direction and column direction. According to this embodiment,
although the pitch in both the row direction and column direction
is made substantially the same pitch, a configuration may be
adopted in which the pitch is substantially the same in only either
one of the row direction and column direction.
[0038] According to this embodiment, although a plurality of pixels
that were arrayed in threes in the row direction and column
direction, respectively, was taken as a single component, the
present invention is not limited thereto, and a configuration may
also be adopted that takes as one component a plurality of pixels
that are arrayed in quantities of 2N+1 or 2N (N is a natural number
of 1 or more) in the row direction and the column direction,
respectively. Further, all pixels of the same color that are
arrayed within a component need not necessarily be added. For
example, in FIG. 3A, although the 3L-1 row and the 3M-1 column were
subjected to thinning, only either one of the 3L-1 row and the 3M-1
column may be thinned (L and M are integers of 1 or more).
[0039] Thus, when the number of pixels to be added is increased,
although the sensitivity increases, the driving frequency
decreases. Accordingly, it is desirable to set the number of pixels
for which a thinning driving operation can be performed within a
range in which the required driving frequency can be obtained.
[0040] Further, if the spatial centroids of pixels to be added are
arrayed at substantially the same pitch, the spatial centroids of
pixels to be added need not necessarily be located in the center of
the pixels after addition. For example, in FIG. 3A, although the
3L-1 row and the 3N-1 column were subjected to thinning, a
configuration may be adopted in which the 3L row and the 3N column
are thinned or the like (L and N are integers of 1 or more).
[0041] However, when the spatial centroids of pixels to be added
are not located in the center of the pixels after addition, the
image quality can deteriorate in comparison with a case where the
spatial centroids are located in the center. Accordingly, it is
desirable that the spatial centroids of pixels to be added are
located in the center of the pixels after addition, although the
present invention is not limited thereto.
[0042] As described above, according to this embodiment, by
arranging the spatial centroid of each pixel to be added at
substantially the same pitch when performing a thinning driving
operation, the moire fringes can be suppressed.
Second Embodiment
[0043] FIGS. 4A and 4B are views illustrating a thinning driving
operation according to a preferred second embodiment of this
invention.
[0044] FIGS. 4A and 4B are views illustrating an example according
to this embodiment in which 25 pixels in five rows by five columns
are taken as a single component 401, and nine pixels of the same
color within the same component are added. As shown in FIG. 4B,
pixels after addition r(1,1), g(1, 2), g(2,1) and b(2,2) are added
based on the respective equations shown in FIG. 4B.
[0045] By adding nine pixel signals within a component in this
manner, the number of pixels to be added increases in comparison to
the first embodiment, and the sensitivity is enhanced. Further,
since the middle pixel rows and pixel columns are subjected to a
thinning driving operation, the vertical and horizontal driving
frequency can be increased to approximately 5/3 and their driving
period can be decreased to approximately 3/5, respectively.
[0046] In this connection, in this embodiment also, if the spatial
centroids of pixels to be added are arrayed at substantially the
same pitch, all pixels of the same color that are arrayed within a
component need not necessarily be added.
[0047] Further, if the spatial centroids of pixels to be added are
arrayed at substantially the same pitch, the spatial centroids of
the pixels to be added need not necessarily be located in the
center of the pixels after addition.
Third Embodiment
[0048] FIGS. 5A and 5B are views that illustrate a thinning driving
operation according to a preferred third embodiment of the present
invention. According to this embodiment, three rows by five columns
are taken as a single component, and driving is performed to thin
out the middle row within the component. FIG. 5B is a view showing
an example of addition in this embodiment. In FIG. 5B, reference
numerals 501r and 501g correspond to one component, respectively.
According to this embodiment, addition is performed by overlapping
each color in the horizontal direction.
[0049] For example, the pixel r1,1 shown in FIG. 5B is obtained by
adding the pixel signals of pixels R(1,1), R(1,3), R(1,5), R(3,1),
R(3,3) and R(3,5) within the component 501r. Likewise, the pixel
g(1,2) shown in FIG. 5B is obtained by adding the pixel signals of
pixels G(1,4), G(1,6), G(1,8), G(3,4), G(3,6) and G(3,8) within the
component 501g. The pixels r(1, 3), g(2,1), g(2,1), b(2,2), g(2, 3)
and the like are determined in a similar manner. In this case,
taking the components 501r and components 501g as an example, the
two components spatially overlap in a manner (row, column)=(1, 4),
(1, 5), (2, 4), (2, 5), (3, 4), (3, 5).
[0050] By allowing a part of the components to overlap spatially
and adding in this way, the sensitivity can be enhanced even
further. Also, since the centroids in the spatial sampling between
color signals in the horizontal direction that were added are at
substantially the same pitch, moire fringes can be reduced.
[0051] Although the present embodiment has taken three rows by five
columns as a single component, the invention is not limited
thereto, and a configuration may be adopted in which a plurality of
pixels are arrayed in quantities of 2N+1 or 2N (N is a natural
number of 1 or more) in the row direction and the column direction,
respectively. Also, although the middle row within each component
was the object of a thinning driving operation, another row within
each component (i.e. an odd row inside the component) may be the
object of a thinning driving operation either instead of or in
addition to the middle row.
[0052] To increase the driving frequency further, the middle column
may also be thinned, and another column (i.e., an odd column inside
the component) may be subjected to a thinning driving operation
either instead of or in addition to the middle row.
[0053] In this embodiment also, if spatial centroids of pixels to
be added are arrayed at substantially the same pitch, it is not
always necessary to add all pixels of the same color that are
arrayed within a component.
[0054] Further, the spatial centroids of pixels to be added need
not necessarily be located in the center of the pixels after
addition.
[0055] [Example of Internal Structure of Imaging Apparatus]
[0056] Next, an example of the internal structure of an imaging
apparatus will be described. FIG. 6 is a block diagram of an
imaging apparatus according to a preferred embodiment of this
invention. In FIG. 6, pixel units that include a pixel amplifier
and a photodiode for photoelectric conversion as shown in FIG. 12
and FIG. 13 to be described later are arrayed in a matrix shape in
the imaging area. The pixel units of this imaging area are
controlled by a plurality of drive pulses that are output from a
vertical scanning circuit (V.SR) 10. The odd-numbered vertical
signal lines of the imaging area are connected to a circuit 20-1
that includes a CDS, an amplifier circuit and a memory, and the
even-numbered vertical signal lines are connected to a circuit 20-2
that includes a CDS, an amplifier circuit and a memory. In the
following description, signals R and signals G of odd-numbered
columns are transferred in sequence to the upper circuit of the
imaging area in FIG. 6, and signals G and signals B of
even-numbered columns are transferred in sequence to the lower
circuit thereof. However, since the upper and lower circuits have
the same configuration, a description is only provided for the
lower circuit block, and a description of the upper circuit block
is omitted.
[0057] With respect to a signal from the pixel unit, the noise
thereof is removed by the CDS and the amplifier circuit, and only
the signal component is amplified and then temporarily stored in
the memory. According to this embodiment, although not illustrated
in the drawings, a circuit for correcting an offset variation may
be provided between amplifier circuits. When the present imaging
apparatus is in an all pixel readout mode, and not an addition and
readout mode, signals from memory are controlled by scanning pulses
.phi.hn (.phi.hn (1), .phi.hn (2), .phi.hn (3)) from a horizontal
scanning circuit (H.SR), and readout to an output signal line. When
in an addition and readout mode, signals from memory are guided to
an adding circuit 30-1. In the adding circuit 30-1, signals of the
same color from the memory are added. Signals that were added in
the adding circuit 30-1 are controlled by scanning pulses .phi.hn
(a1, a2) from a horizontal scanning circuit (H.SR), and readout to
an output signal line.
[0058] FIG. 12 is a circuit diagram of a unit pixel of the pixel
unit, FIG. 7 is a circuit diagram of one part of a readout signal
processing circuit for pixel signals from the imaging area, and
FIG. 11 is a timing chart for the addition of pixel signals.
Hereunder, signal addition and signal readout from the pixel unit
will be described using FIG. 7, FIG. 11 and FIG. 12. In this
connection, FIG. 7 is a schematic circuit diagram for implementing
the method of addition shown in FIGS. 3A and 3B. The pixel unit
shown in FIG. 12 includes a photodiode PD, a transfer switch MTX, a
pixel amplifier MSF, a reset switch MRES, and a select switch MSEL.
The photodiode PD functions as a photoelectric conversion unit.
Transfer of signal charge from the photodiode PD is controlled by
the transfer switch MTX. The pixel amplifier MSF is connected to
the transfer switch MTX. The reset switch MRES resets a residual
charge of a gate unit (floating diffusion) of the pixel amplifier
MSF. The select switch MSEL controls the transfer of a signal
charge from the pixel amplifier MSF. A current source switch MRV of
the pixel amplifier MSF is provided outside the imaging area.
[0059] Next, the readout signal processing circuit shown in FIG. 7
will be described. A CDS (Correlated Double Sampling) circuit
includes clamp capacities C1, C3, and C5, clamp switches MC1, MC3,
MC5, a voltage reference Vr, and amplifiers Amp1, Amp3, and Amp5.
The CDS circuit removes noise of the pixel unit. The clamp
capacities C1, C3 and C5 are connected to vertical signal lines L1,
L3 and L5. Memory capacitors Ct1, Ct2, and Ct3 of the memory
circuit temporarily store signals that were sampled according to
the CDS method. A memory capacitor Ca1 adds two signals of a memory
and temporarily stores the result. Similarly, a memory capacitor
Ca2 temporarily stores an addition signal of different horizontal
pixel rows. Addition of signals is performed by connecting the
output ends of the memory capacitors Ca1 and Ca2. In FIG. 7, since
the addition of signals is not performed with the vertical signal
line L5, an addition memory is not provided. As described above, in
FIG. 6 and FIG. 7, thinning and addition of signals was performed
within an image sensor (sensor). In high speed imaging this method
is advantageous. However, as a separate method, thinning of signals
may be carried out in the same manner within an image sensor
(sensor), while the addition of signals may be carried out inside a
memory of a signal processing circuit 73 as shown in FIG. 14.
[0060] Next, a description will be provided using the timing chart
of FIG. 10. First, after an arbitrary exposure period passes, a
residual charge in a node of each circuit part is reset by control
of respective pulses.
[0061] At a time t1, the gate unit of the pixel amplifier MSF is
reset by a pulse .phi.RES, the memory Ct is reset by pulses .phi.C1
and .phi.TS1, and adding unit capacitors Ca1 and Ca2 are reset by
pulses .phi.AD1, .phi.AD2, .phi.AD3 and .phi.C2. At a time t2, when
the pulse .phi.C1 is OFF the pixel amplifier noise is clamped by
clamp capacitors C1 to C3, and a charge of the photodiode PD is
input to the clamp capacitors C1 to C3 via the pixel amplifier MSF
by means of a pulse .phi.TX.
[0062] As a result, pixel noise is subjected to CDS removal, and
signals are temporarily stored in the memory via the amplifier Amp.
In this case, if vertical scanning is assumed to be scanning of N
rows as shown in FIGS. 3A and 3B, as a result of signals from
vertical signal lines L1 and L3, signals R(1,1) and R(1,3) are
temporarily stored in memory capacitors Ct1 and Ct3,
respectively.
[0063] At a time t3, as a result of pulses .phi.SEL and .phi.TS1
being OFF, transfer of photoelectric conversion signals of N row
pixels ends.
[0064] At a time t4, memory signals R(1,1) and R(1,3) are added in
the adding memory capacitor Ca1 as a result of pulses .phi.TS2 and
.phi.AD1. Subsequently, the N+1 row is subjected to skip scanning,
and by performing the same scanning and operation for the N+2 row
as the N row, at a time t5 the pixel signals R(3,1) and R(3,3) of
the N+2 row are added in the memory capacitor Ca2. At a time t6,
the signals of four pixels R(1,1), R(1,3), R(3,1) and R(3,3) are
added at a pulse (pAD3, to obtain an addition signal r(1,1).
Although a description is omitted here, as a consequence other
addition signals g(1,2), r(1,3) and g(1,4) are also formed. The
same operation is repeated to form addition signals within the
screen.
[0065] In the addition and readout mode, for four pixels as
described above, since the sensitivity is improved twofold (light
shot noise), exposure amount control is performed for the system
and the amount of incident light is set to approximately 1/2. This
means that the photoelectric conversion signal of each photodiode
becomes 1/2. When the imaging apparatus uses a CCD, even if the
amount of incident light is 1/2, by adding the charges of four
pixels, the signal charge amount after addition is doubled.
Accordingly, in this state, signal saturation becomes a problem and
there is a drawback that there is a tradeoff between sensitivity
and saturation characteristics.
[0066] With the CMOS sensor of this embodiment, in order to add the
mean value of the signal voltage, if a drop in the signal level due
to capacitor division is disregarded, the signal level also becomes
approximately 1/2 after addition of the four pixel signals. This
means that the signal saturation was strengthened twofold. However,
when the signal level is low, noise of an output amplifier (omitted
from FIG. 7) that connects to a horizontal output line may become a
problem. Therefore, according to a preferred embodiment of this
invention, when the apparatus is in the addition and readout mode,
the amplifier gain of the amplifier circuit Amp after CDS is set to
approximately twice that at the time of all pixel readout mode. As
a result, it is possible to alleviate noise of the output amplifier
and to realize lower power levels and maintenance of a high dynamic
range and high speed readout by reducing the number of readout
pixels and increasing sensitivity by adding the pixel signals.
[0067] FIG. 8 illustrates an embodiment of a signal readout method
in the addition and readout mode. FIG. 8 shows an example of signal
readout in multiple row units that are to be added. In this case,
signals are readout from pixels in the row units to be added, and
addition (Ca) with the signal memory (Ct) is performed. Thereafter,
signals are output to the outside from two addition memories Ca
within a horizontal scanning period.
[0068] FIG. 9 is a view illustrating a case that utilizes a
mechanical shutter. In this case, all pixels of the imaging area
are reset in one batch over the whole area, and after exposure ends
with the mechanical shutter, pixel signals are output to the
outside with an arbitrary addition unit from a memory after
addition 2 in one horizontal scanning period.
[0069] FIG. 11 shows a timing example for readout of all pixel
signals. According to this embodiment, the pixel amplifier and
memory are reset at a time t1, clamping of the pixel amplifier
noise potential is performed at a time t2, and CDS processing ends
and signals are stored in memory Ct at a time t3. From a time t4
and thereafter, signals are readout to a horizontal signal output
line.
[0070] FIG. 12 shows a configuration in which one pixel amplifier
is provided for one photodiode as the pixel unit of an imaging
area. FIG. 13 shows a configuration using a shared amplifier pixel
as another embodiment of a pixel unit. This is an example in which
a plurality of photodiodes is provided with respect to a single
pixel amplifier. When a plurality of photodiodes PD1, PD2 and PD3
are disposed with respect to a single amplifier, the area of the
pixel amplifier with respect to a single photodiode decreases.
Consequently there is an effect that the aperture ratio of the
photodiode increases. In this connection, although according to
this embodiment a configuration was described in which three
photodiodes are provided with respect to one pixel amplifier, the
invention is not limited thereto, and an arbitrary number of
photodiodes can be provided with respect to a single pixel
amplifier.
[0071] FIG. 14 is a view illustrating an outline of an imaging
system that uses the above described imaging apparatus. This
imaging system includes an imaging apparatus 700 that consists of a
sensor 72, a signal processing circuit 73 and a timing control
circuit 75. As shown in the figure, light of an object that was
incident through an optical system 71 forms an image on the sensor
72. Light information from pixels disposed on the sensor is
converted into an electrical signal. The electrical signal is
subjected to signal conversion processing according to a
predetermined method by the signal processing circuit 73. The
signals that underwent signal processing are communicated to or
recorded by an information recording apparatus by means of a
recording system and communication system 74. Playback or display
of the recorded or transferred signals is performed at a playback
system and display system 77. The sensor 72 and the signal
processing circuit 73 are controlled by the timing control circuit
75, and the timing control circuit 75, the recording system and
communication system 74 and the playback system and display system
77 are controlled by a system control circuit 76. Selection of all
pixel readout mode or addition and readout mode is performed by the
timing control circuit 75.
[0072] In the aforementioned all pixel readout mode and the
addition and readout mode, the horizontal and vertical drive pulses
are different. Accordingly, it is necessary to change the drive
timing of the sensor, resolution processing of the signal
processing circuit, and the number of recording pixels of the
recording system for the respective readout modes. These control
operations are performed in accordance with the respective readout
mode at the system control circuit. Further, the sensitivity
resulting from addition differs in the readout modes. In this case,
aperture (not shown) control is performed at the system control
circuit, and switching is also performed with a control pulse (not
shown) from the timing control circuit so as to increase the gain
of the amplifier circuit Amp of the sensor to obtain an appropriate
signal.
[0073] According to the present imaging system, all pixel readout
is carried out for high definition imaging, and for low resolution
imaging a high sensitivity is produced by adding pixel signals,
high speed readout is produced by thinning driving, and the
sampling pitches of signals after addition are made substantially
the same pitch so that a high image quality can be obtained.
[0074] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0075] This application claims the benefit of Japanese Patent
Application No. 2005-321398 filed on Nov. 4, 2005, which is hereby
incorporated by reference herein in its entirety.
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