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Digital Camera Patent Abstract
A digital camera 100 includes an imaging device having a plurality
of unit cells, each generating and accumulating therein a piece
of luminance information in accordance with an amount of received
light. The imaging device comprises: a receiving unit 103 operable
to receive a shooting instruction from outside; an all-reset unit
104 operable to simultaneously reset all the unit cells in response
to the shooting instruction while a light-shielding gate is open;
a light-shielding unit 101 operable to close the light-shielding
gate to simultaneously block light incident on all the unit cells
when, after the all-reset unit resets all the unit cells, a total
length of periods for which the light-shielding gate has been open
reaches an exposure time; and a reading unit 105 operable to sequentially
read pieces of the luminance information from all the unit cells
while the light-shielding gate is closed.
Digital Camera Patent Claims
1. An imaging device having a plurality of unit cells, each generating
and accumulating therein a piece of luminance information in accordance
with an amount of received light, the imaging device comprising:
a receiving unit operable to receive a shooting instruction from
outside; an all-reset unit operable to simultaneously reset all
the unit cells in response to the shooting instruction while a light-shielding
gate is open; a light-shielding unit operable to close the light-shielding
gate to simultaneously block light incident on all the unit cells
when, after the all-reset unit resets all the unit cells, a total
length of periods for which the light-shielding gate has been open
reaches an exposure time; and a reading unit operable to sequentially
read pieces of the luminance information from all the unit cells
while the light-shielding gate is closed.
2. The imaging device of claim 1, wherein the light-shielding unit
closes the light-shielding gate at a time determined independently
of a change of the exposure time, and the all-reset unit adjusts
a timing with which the all-reset unit resets all the unit cells,
in accordance with the change of the exposure time.
3. The imaging device of claim 1 further comprising: a monitor
unit operable, before the shooting instruction is received by the
receiving unit, to display moving pictures by continuously reading
the pieces of the luminance information while the light-shielding
gate is open, and when the shooting instruction is received, to
stop a pixel reset operation and a luminance information reading
operation, which are performed every time the luminance information
is read, at least until the reading unit finishes reading the pieces
of the luminance information.
4. The imaging device of claim 3, wherein the monitor unit applies
a pixel reset signal and a luminance information reading signal
to read the pieces of the luminance information, and stops applying
the pixel reset signal and the luminance information reading signal
at least during a period between when the all-reset unit resets
all the unit cells and when the light-shielding unit blocks the
light.
5. The imaging device of claim 4, wherein the monitor unit includes
a shift register operable to sequentially generate the pixel reset
signal and the luminance information reading signal for each column
of the imaging device, and stops an operation of the shift register
at least during the period between when the all-reset unit resets
all the unit cells and when the light-shielding unit blocks the
light.
6. The imaging device of claim 5, wherein the shift register sequentially
generates the pixel reset signal and the luminance information reading
signal for each column of the imaging device while sequentially
shifting a target column to which a start pulse is provided for
each frame, and the monitor unit stops the start pulse in response
to the shooting instruction at least until when the light-shielding
unit blocks the light.
7. The imaging device of claim 5, wherein the all-reset unit simultaneously
resets all the unit cells in a period between when the shift register
finishes generating the pixel reset signal and the luminance information
reading signal for each column and when the light-shielding unit
blocks the light.
8. The imaging device of claim 3, wherein to read the pieces of
the luminance information, the monitor unit applies a first pixel
reset pulse used for an electronic shutter, a first pixel reading
pulse used for the electronic shutter, a second pixel reset pulse
used for reading image signals and a second pixel reading pulse
used for reading image signals, and stops applying the first pixel
reading pulse and the second pixel reading pulse at least during
a period between when the all-reset unit resets all the unit cells
and when the light-shielding unit blocks the light.
9. The imaging device of claim 3, wherein to read the pieces of
the luminance information, the monitor unit applies a first pixel
reset pulse used for an electronic shutter, a first pixel reading
pulse used for the electronic shutter, a second pixel reset pulse
used for reading image signals and a second pixel reading pulse
used for reading image signals, and stops applying the first pixel
reset pulse, the first pixel reading pulse, the second pixel reset
pulse and the second pixel reading pulse at least during a period
between when the all-reset unit resets all the unit cells and when
the light-shielding unit blocks the light.
10. The imaging device of claim 3, wherein to read the pieces of
the luminance information, the monitor unit applies a pixel reset
pulse used for an electronic shutter and a pixel reading pulse used
for the electronic shutter, and stops applying the pixel reading
pulse during a period between when the all-reset unit resets all
the unit cells and when the reading unit finishes reading the pieces
of the luminance information.
11. The imaging device of claim 3, wherein to read the pieces of
the luminance information, the monitor unit applies a pixel reset
pulse used for an electronic shutter and a pixel reading pulse used
for the electronic shutter, and stops applying the pixel reset pulse
and the pixel reading pulse during a period between when the all-reset
unit resets all the unit cells and when the reading unit finishes
reading the pieces of the luminance information.
12. The imaging device of claim 3, wherein the monitor unit includes
a shift register operable to sequentially generate the pixel reset
signal for each column of the imaging device, and stops an operation
of the shift register during a period between when the all-reset
unit resets all the unit cells and when the reading unit finishes
reading the pieces of the luminance information.
13. The imaging device of claim 12, wherein the shift register
sequentially generates the pixel reset signal for each column of
the imaging device while sequentially shifting a target column to
which a start pulse is provided for each frame, and the monitor
unit stops the start pulse in response to the shooting instruction
until the reading unit finishes reading the pieces of the luminance
information.
14. The imaging device of claim 12, wherein the imaging device
further comprises: a unit cell driving circuit operable to generate
a pulse used for driving the unit cells, based on a signal provided
by the all-reset unit to reset all the unit cells and a signal provided
by the monitor unit to perform the pixel reset operation, and provide
each of the unit cells with the generated pulse, and each of the
shift register and the selection circuit is structured by a dynamic
circuit using a single channel MOS.
15. The imaging device of claim 1, wherein the all-reset unit resets
all the unit cells at any time in one cycle of a horizontal scanning,
regardless of whether the time is within a horizontal blanking period.
16. A driving device that provides control signals to an imaging
device having a plurality of unit cells, each outputting a piece
of luminance information in accordance with an amount of received
light, the driving device comprising: a waiting unit operable to
wait for a shooting instruction to be input from outside; an all-reset
control signal outputting unit operable to output an all-reset control
signal to simultaneously reset all the unit cells in response to
the shooting instruction while a light-shielding gate is open; a
closing control signal outputting unit operable to output a light-shielding
gate closing control signal to close the light-shielding gate that
blocks light incident on all the unit cells when, after the all-reset
unit resets all the unit cells, a total length of periods for which
the light-shielding gate has been open reaches an exposure time;
and a reading control signal outputting unit operable to output
a reading control signal to sequentially read the pieces of the
luminance information from all the unit cells while the light-shielding
gate is closed.
17. An imaging method for controlling an imaging device having
a plurality of unit cells, each outputting a piece of luminance
information in accordance with an amount of received light, the
imaging method comprising: a receiving step of receiving a shooting
instruction from outside; an all-reset step of simultaneously resetting
all the unit cells in response to the shooting instruction while
a light-shielding gate is open; a light-shielding step of closing
the light-shielding gate to simultaneously block light incident
on all the unit cells when, after the all-reset unit resets all
the unit cells, a total length of periods for which the light-shielding
gate has been open reaches an exposure time; and a reading step
of sequentially reading pieces of the luminance information from
all the unit cells while the light-shielding gate is closed.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
[0001] (1) Field of the Invention
[0002] The present invention relates to an imaging device including
unit cells, which are one-dimensionally or two-dimensionally disposed
on a substrate and subject incident light to photoelectric conversion.
The present invention particularly relates to a technique to prevent
a distortion of an image of a moving subject.
[0003] (2) Description of the Related Art
[0004] In recent years, imaging apparatuses, such as portable phones
having a digital camera function, have been widely spread. In such
apparatuses, it is necessary to save power consumption to save weight
and extend the use time in the case of continuous use. Therefore,
MOS type imaging devices, which consume significantly lower power
than the CCD type imaging devices, are often used in such apparatuses.
[0005] In conventional MOS type imaging devices, electric charges
are read from each line, and an exposure timing might be different
for each line. Accordingly, the taken image might be distorted due
to the motion of a subject.
[0006] Patent Document 1 (Japanese Laid-open Patent Application
NO. 2004-64558) discloses an imaging device that overcomes such
a fault. This document asserts that high-quality images can be obtained
by the disclosed imaging device.
[0007] However, this imaging device can merely reduce the distortion
of the image, which is caused by the difference of exposure timing
among lines, to the extent that it is imperceptible to human-eye,
and can not eliminate the distortion completely. Also, this technique
is developed for the case of shooting moving pictures, and it can
not gain a sufficient effect in the case of shooting still pictures.
[0008] Further, to structure a peripheral circuit by a single channel
MOS, a dynamic circuit is often used. If this is the case, the circuit
is liable to malfunction due to the floating status. Therefore,
to reset all the unit cells at the same time by an electronic shutter
to adjust the exposure start timing, some measures need to be taken.
SUMMARY OF THE INVENTION
[0009] The object of the present invention is therefore to provide
an imaging device having different exposure timings, but capable
of completely eliminating a distortion of an image due to the difference
of the exposure timings and preventing misoperation of a dynamic
circuit using a single channel MOS.
[0010] The above object is fulfilled by an imaging device having
a plurality of unit cells, each generating and accumulating therein
a piece of luminance information in accordance with an amount of
received light, the imaging device comprising: a receiving unit
operable to receive a shooting instruction from outside; an all-reset
unit operable to simultaneously reset all the unit cells in response
to the shooting instruction while a light-shielding gate is open;
a light-shielding unit operable to close the light-shielding gate
to simultaneously block light incident on all the unit cells when,
after the all-reset unit resets all the unit cells, a total length
of periods for which the light-shielding gate has been open reaches
an exposure time; and a reading unit operable to sequentially read
pieces of the luminance information from all the unit cells while
the light-shielding gate is closed.
[0011] The light-shielding unit may close the light-shielding gate
at a time determined independently of a change of the exposure time,
and the all-reset unit may adjust a timing with which the all-reset
unit resets all the unit cells, in accordance with the change of
the exposure time.
[0012] The imaging device may further comprise: a monitor unit
operable, before the shooting instruction is received by the receiving
unit, to display moving pictures by continuously reading the pieces
of the luminance information while the light-shielding gate is open,
and when the shooting instruction is received, to stop a pixel reset
operation and a luminance information reading operation, which are
performed every time the luminance information is read, at least
until the reading unit finishes reading the pieces of the luminance
information.
[0013] The monitor unit may apply a pixel reset signal and a luminance
information reading signal to read the pieces of the luminance information,
and stop applying the pixel reset signal and the luminance information
reading signal at least during a period between when the all-reset
unit resets all the unit cells and when the light-shielding unit
blocks the light.
[0014] The monitor unit may include a shift register operable to
sequentially generate the pixel reset signal and the luminance information
reading signal for each column of the imaging device, and may stop
an operation of the shift register at least during the period between
when the all-reset unit resets all the unit cells and when the light-shielding
unit blocks the light.
[0015] The shift register may sequentially generate the pixel reset
signal and the luminance information reading signal for each column
of the imaging device while sequentially shifting a target column
to which a start pulse is provided for each frame, and the monitor
unit may stop the start pulse in response to the shooting instruction
at least until when the light-shielding unit blocks the light.
[0016] The all-reset unit may simultaneously reset all the unit
cells in a period between when the shift register finishes generating
the pixel reset signal and the luminance information reading signal
for each column and when the light-shielding unit blocks the light.
[0017] To read the pieces of the luminance information, the monitor
unit may apply a first pixel reset pulse used for an electronic
shutter, a first pixel reading pulse used for the electronic shutter,
a second pixel reset pulse used for reading image signals and a
second pixel reading pulse used for reading image signals, and may
stop applying the first pixel reading pulse and the second pixel
reading pulse at least during a period between when the all-reset
unit resets all the unit cells and when the light-shielding unit
blocks the light.
[0018] To read the pieces of the luminance information, the monitor
unit may apply a first pixel reset pulse used for an electronic
shutter, a first pixel reading pulse used for the electronic shutter,
a second pixel reset pulse used for reading image signals and a
second pixel reading pulse used for reading image signals, and may
stop applying the first pixel reset pulse, the first pixel reading
pulse, the second pixel reset pulse and the second pixel reading
pulse at least during a period between when the all-reset unit resets
all the unit cells and when the light-shielding unit blocks the
light.
[0019] To read the pieces of the luminance information, the monitor
unit may apply a pixel reset pulse used for an electronic shutter
and a pixel reading pulse used for the electronic shutter, and may
stop applying the pixel reading pulse during a period between when
the all-reset unit resets all the unit cells and when the reading
unit finishes reading the pieces of the luminance information.
[0020] To read the pieces of the luminance information, the monitor
unit may apply a pixel reset pulse used for an electronic shutter
and a pixel reading pulse used for the electronic shutter, and may
stop applying the pixel reset pulse and the pixel reading pulse
during a period between when the all-reset unit resets all the unit
cells and when the reading unit finishes reading the pieces of the
luminance information.
[0021] The monitor unit may include a shift register operable to
sequentially generate the pixel reset signal for each column of
the imaging device, and may stop an operation of the shift register
during a period between when the all-reset unit resets all the unit
cells and when the reading unit finishes reading the pieces of the
luminance information.
[0022] The shift register may sequentially generate the pixel reset
signal for each column of the imaging device while sequentially
shifting a target column to which a start pulse is provided for
each frame, and the monitor unit may stop the start pulse in response
to the shooting instruction until the reading unit finishes reading
the pieces of the luminance information.
[0023] The imaging device may further comprise: a unit cell driving
circuit operable to generate a pulse used for driving the unit cells,
based on a signal provided by the all-reset unit to reset all the
unit cells and a signal provided by the monitor unit to perform
the pixel reset operation, and provide each of the unit cells with
the generated pulse, and each of the shift register and the selection
circuit may be structured by a dynamic circuit using a single channel
MOS.
[0024] The all-reset unit may reset all the unit cells at any time
in one cycle of a horizontal scanning, regardless of whether the
time is within a horizontal blanking period.
[0025] The above object is also fulfilled by a driving device that
provides control signals to an imaging device having a plurality
of unit cells, each outputting a piece of luminance information
in accordance with an amount of received light, the driving device
comprising: a waiting unit operable to wait for a shooting instruction
to be input from outside; an all-reset control signal outputting
unit operable to output an all-reset control signal to simultaneously
reset all the unit cells in response to the shooting instruction
while a light-shielding gate is open; a closing control signal outputting
unit operable to output a light-shielding gate closing control signal
to close the light-shielding gate that blocks light incident on
all the unit cells when, after the all-reset unit resets all the
unit cells, a total length of periods for which the light-shielding
gate has been open reaches an exposure time; and a reading control
signal outputting unit operable to output a reading control signal
to sequentially read the pieces of the luminance information from
all the unit cells while the light-shielding gate is closed.
[0026] The above object is also fulfilled by an imaging method
for controlling an imaging device having a plurality of unit cells,
each outputting a piece of luminance information in accordance with
an amount of received light, the imaging method comprising: a receiving
step of receiving a shooting instruction from outside; an all-reset
step of simultaneously resetting all the unit cells in response
to the shooting instruction while a light-shielding gate is open;
a light-shielding step of closing the light-shielding gate to simultaneously
block light incident on all the unit cells when, after the all-reset
unit resets all the unit cells, a total length of periods for which
the light-shielding gate has been open reaches an exposure time;
and a reading step of sequentially reading pieces of the luminance
information from all the unit cells while the light-shielding gate
is closed.
[0027] With the stated structure, although the luminance information
is not read from all the unit cells at the same time, it becomes
possible to completely synchronize the exposure timings of all the
unit cells. This is because all the unit cells are reset at the
same time by the electronic shutter, and the light incident on all
the unit cells is blocked at the same time by the light-shielding
gate, such as a mechanical shutter. Accordingly, the present invention
is capable of completely eliminating a distortion of an image caused
due to the difference of the exposure timings, and capable of gaining
high-quality still pictures.
[0028] Also, the present invention is capable of adjusting the
exposure time by just changing the reset timing of the electronic
shutter while the closing timing of the light-shielding gate is
fixed. Therefore, it becomes easy to control and adjust the exposure
time accurately.
[0029] Also, in the case where the pixel reading pulse used for
the electronic shutter (ETRANS) and the pixel reading pulse used
for reading image signals (TRANS) are not applied, the exposure
time of all the pixels can be the same. Even if the SR output used
for reading, or the SR output used for the electronic shutter misoperates
in the dynamic circuit structured by the signal channel MOS, TROUT
can be kept at "LOW". This is very effective for the prevention
of misoperations of the imaging device.
[0030] Also, in the case where the pixel reset pulse used for the
electronic shutter (ERSCELL) and the pixel reset pulse used for
reading image signals (RSCELL) are not applied, the present invention
is capable of suppressing a leak caused due to change in potential
in a floating fusion unit (an FD unit) from which to read the luminance
information. Even if the SR output used for reading, or the SR output
used for the electronic shutter misoperates in the dynamic circuit
structured by the single channel MOS, TROUT can be kept at "LOW".
This is very effective for the prevention of misoperations of the
imaging device.
[0031] Further, in the case of stopping the pixel reset pulse used
for the electronic shutter (ERSCELL) to record still pictures, the
all-reset unit 104 can reset the pixels at any time in one cycle
of the horizontal scanning, regardless of whether the time is within
the horizontal blanking period. Accordingly, the present invention
is capable of flexibly controlling the application of the pulses.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] These and the other objects, advantages and features of
the invention will become apparent from the following description
thereof taken in conjunction with the accompanying drawings which
illustrate a specific embodiment of the invention.
In the drawings:
[0033] FIG. 1 shows a digital camera 100 according to the first
embodiment of the present invention;
[0034] FIG. 2 schematically shows a structure of a solid-state
imaging device;
[0035] FIG. 3 schematically shows a structure of circuits included
in a pixel group 1;
[0036] FIG. 4 schematically shows a circuit structure of a unit
register included in a shift register 2 used for an electronic shutter;
[0037] FIG. 5 is a timing chart for operations of a shift register
2 used for an electronic shutter;
[0038] FIG. 6 shows a logical circuit of a first stage included
in a multiplexer circuit 4;
[0039] FIG. 7 schematically shows a circuit structure of a first
stage included in a multiplexer circuit 4;
[0040] FIG. 8 shows a functional structure of a digital camera
100 according to the first embodiment of the present invention;
[0041] FIG. 9 shows a processing procedure performed by a digital
camera 100 according to the first embodiment to take a still picture;
[0042] FIG. 10 is an example timing chart for control pulses and
so on used in a digital camera 100 according to the first embodiment;
[0043] FIG. 11 is another example timing chart for control pulses
and so on used in a digital camera 100 according to the first embodiment;
[0044] FIG. 12 is another example timing chart for control pulses
and so on used in a digital camera 100 according to the first embodiment;
[0045] FIG. 13 shows a processing procedure performed to take a
still picture according to the first modification of the present
invention;
[0046] FIG. 14 is a timing chart for control pulses and so on according
to the first modification;
[0047] FIG. 15 shows a processing procedure performed to take a
still picture according to the second modification;
[0048] FIG. 16 is a timing chart for control pulses and so on according
to the second modification; and
[0049] FIG. 17 is a timing chart for an all-reset pulse and so
on according to the third modification.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The First Embodiment
<Overview>
[0050] The first embodiment of the present invention uses an electronic
shutter and a mechanical shutter together. Although not able to
read luminance information from all the unit cells at the same time,
this embodiment can exactly synchronize exposure timings of all
the unit cells to completely eliminate distortion of an image. Also,
this embodiment easily and accurately controls the exposure time.
<Structure>
[0051] FIG. 1 shows a digital camera 100 according to the first
embodiment of the present invention.
[0052] As FIG. 1 shows, the digital camera 100 according to the
first embodiment is an imaging apparatus that is capable of taking
still pictures while displaying moving pictures on a display panel,
such as an LCD (not illustrated). The digital camera 100 includes
a light-shielding device 10, a solid-state imaging device 20 and
a drive control device 30.
[0053] The light-shielding device 10 is a mechanical shutter or
the like, and disposed in a light path behind a lens for instance.
The light-shielding device 10 is an openable and closable light-shielding
gate which blocks light using a light-shielding plate when it is
in a closed status, and gets through light when it is in an opened
status. The light-shielding device 10 can synchronously get through
light entering the unit cells on the solid-state imaging device
20 (by changing the status from the closed status to the opened
status), and block the light (by changing the status from the opened
status to the closed status) in accordance with a control signal
input from the drive control device 30.
[0054] Here, note that the light-shielding device is not limited
to a mechanical shutter. It is possible to replace the mechanical
shutter with any other mechanism as long as it can block light in
the closed status and get through light in the opened status.
[0055] The solid-state imaging device 20 includes a semiconductor
device and peripheral circuits. A plurality of unit cells, each
of which outputs luminance information in accordance with the amount
of received light, are arranged in the semiconductor device. The
solid-state imaging device 20 is disposed where an image is formed
by the light passing through the light-shielding device 10.
[0056] FIG. 2 schematically shows a structure of the solid-state
imaging device 20 according to the first embodiment of the present
invention.
[0057] As FIG. 2 shows, the solid-state imaging device 20 according
to the first embodiment of the present invention includes pixel
group 1, a shift register 2 used for an electronic shutter, a shift
register 3 used for reading image signals, a multiplexer circuit
4, a horizontal reading circuit 5, and a final amplifier 6.
[0058] FIG. 3 schematically shows the structure of the circuits
included in the pixel group 1.
[0059] The pixel group 1 constitutes an imaging region in which
unit cells are one-dimensionally or two dimensionally disposed.
In FIG. 2 and FIG. 3, only twenty five unit cells, which are two-dimensionally
disposed in a 5.times.5 matrix shape, are illustrated for simplification.
However, the actual number of the unit cells is hundreds to thousands
in the case of the one-dimension arrangement, and hundreds of thousands
to millions in the case of the two-dimension arrangement.
[0060] The shift register 2 used for the electronic shutter sequentially
shifts a target column to which the start pulse used for the electronic
shutter is provided by the drive control device 30 for each frame,
and thereby sequentially generates column address signals used for
the electronic shutter, to read the luminance information and record
moving pictures.
[0061] The shift register 3 used for reading image signals sequentially
shifts a target column to which the start pulse used for reading
image signals is provided by the drive control device 30 for each
frame, and thereby sequentially generate column address signals
used for reading image signals, to read the luminance information
and record moving pictures and still pictures.
[0062] If the user presses the shutter button to give an instruction
to record a still picture, the drive control device 30 stops the
start pulse used for the electronic shutter, which is provided to
the shift register 2 used for the electronic shutter, and stops
the start pulse used for reading image signals, which is provided
to the shift register 3 used for reading image signals. As a result,
the drive control device 30 stops the generation of the column addresses
used for the electronic shutter and the column addresses used for
reading image signals, and deactivates a moving pictures displaying
function.
[0063] FIG. 4 schematically shows a circuit structure of a unit
register included in the shift register 2 used for the electronic
shutter. Although only five stages are illustrated in FIG. 4, the
actual number of the stages is the same as the number of columns
included in the pixel group 1, which is hundreds to thousands.
[0064] As FIG. 4 shows, the shift register 2 used for the electronic
shutter is structured by a dynamic circuit using a single channel
MOS.
[0065] FIG. 5 is a timing chart for operations of the shift register
2 used for the electronic shutter.
[0066] The following describe the operations performed by the shift
register 2 used for the electronic shutter.
[0067] When the start pulse used for the electronic shutter becomes
"High" and the clock pulse (Clk) changes from "Low"
to "High", the capacitor C1 boosts up the gate voltage
of the TR1-1 (IN).
[0068] Due to the high voltage applied to the gate of the TR1-1,
the "High" voltage of the clock pulse (Clk) is output
to OUT1. Also as a high voltage is also applied to the gate of the
TR1-2, the "High" voltage is output to the NEXT1.
[0069] Then, when the clock pulse (Clk) changes from "High"
to "Low", the "Low" voltage of the clock pulse
(Clk) is output to the OUT1, while the NEXT 1 keeps the "High"-voltage
because the TR-1-2 is a unidirectional device.
[0070] After that, the above-described operations are repeated
for each clock pulse (Clk) in the order from the second stage to
the fifth stage, and voltages are sequentially output to the OUT1
to the OUT5.
[0071] The circuit structure and the operations of the shift register
3 used for reading image signals are the same as the shift register
2 used for the electronic shutter. Therefore, their descriptions
are omitted here.
[0072] The multiplexer circuit 4 is a logical circuit that generates
pulses used for driving unit cells based on the all-reset pulse
(ALLRS) and the SR output used for the electronic shutter, and provides
the pulses to the unit cells in column-by-column manner.
[0073] FIG. 6 shows a logical circuit of a first stage included
in the multiplexer circuit 4.
[0074] FIG. 7 schematically shows a circuit structure of the first
stage included in the multiplexer circuit 4.
[0075] As FIG. 7 shows, the multiplexer circuit 4 is structured
by a dynamic circuit using a single channel MOS.
[0076] According to the multiplexer circuit 4 shown in FIG. 6 and
FIG. 7, the RSOUT 1 is output (i) when the all-reset pulse (ALLRS)
and a pixel reset pulse used for the electronic shutter (ERSCELL)
are output at the same time, (ii) when the SR output used for reading
and a pixel reset pulse used for reading image signals (RSCELL)
are output at the same time, and (iii) when the SR output used for
the electronic shutter and the pixel reset pulse used for the electronic
shutter (ERSCELL) are output at the same time. Also, the TROUT 1
is output (i) when the all-reset pulse (ALLRS) and a pixel reading
pulse used for the electronic shutter (ETRANS) are output at the
same time, (ii) when the SR output used for reading and the pixel
reading pulse used for the electronic shutter (ETRANS) are output
at the same time, and (iii) when the SR output used for the electronic
shutter and the pixel reading pulse used for the electronic shutter
(ETRANS) are output at the same time.
[0077] The circuits at the second to fifth stages in the multiplexer
circuit are the same as the circuit at the first stage.
[0078] The drive control unit 30 includes a semiconductor device
and the peripheral circuit, and provides a control signal to the
solid-state imaging device 20 to drive and control the solid-state
imaging device 20. The drive control unit 30 waits for a shooting
instruction to be input. Upon receiving the shooting instruction,
the drive control unit 30 outputs the all-reset pulse (ALLRS) which
resets all the pieces of the luminance information stored in unit
cells while the light-shielding gate is open. When the total length
of periods for which the light-shielding gate has been open reaches
the exposure time, the drive control unit 30 closes the light-shielding
gate and outputs a gate closing control signal used for blocking
light incident on all the unit cells. After closing the light-shielding
gate, the drive control unit 30 outputs a reading control signal
used for sequentially reading the luminance information from all
the unit cells.
[0079] FIG. 8 shows a functional structure of the digital camera
100 according to the first embodiment of the present invention.
[0080] As FIG. 8 shows, the digital camera 100 includes a light-shielding
unit 101, a monitor unit 102, a receiving unit 103, an all-reset
unit 104, and a reading unit 105.
[0081] The structure of the light-shielding unit 101 is the same
as the structure of the light-shielding device 10.
[0082] If the main switch has been pressed, before the receiving
unit 103 receives the shooting instruction, the monitor unit 102
sequentially reads pieces of the luminance information and displays
moving pictures, while the light-shielding gate of the light-shielding
unit 101 is open. If the receiving unit 103 receives the shooting
instruction while the monitor unit 102 displays the moving pictures,
the monitor unit 103 suspends the display of the moving pictures
at least until the reading unit 105 finishes reading the luminance
information.
[0083] The receiving unit 103 waits for an input of a shooting
instruction, which is generated when the shutter button is pressed
by the user for instance and input from outside the imaging device.
Upon receiving the shooting instruction, the receiving unit 103
instructs the monitor unit 102 to suspend the display of the moving
pictures, and instructs other units to start shooting a still picture
in synchronization with the operation of the monitor unit 102.
[0084] If the receiving unit 103 receives the shooting instruction,
the all-reset unit 104 resets all the pieces of the luminance information
stored in the unit cells, while the light-shielding gate of the
light-shielding unit 101 is open.
[0085] The all-reset unit 104 obtains an exposure time by, for
instance, obtaining the image signals used for displaying the moving
picture, receiving a manual setting from the user, or measuring
an amount of light reflected from a subject using a photometer sensor.
Then, the all-reset unit 104 changes the reset timing according
to the obtained exposure time, and adjusts the exposure time.
[0086] After the all-reset unit 104 resets the luminance information,
the light-shielding unit 101 closes the light-shielding gate in
accordance with the shooting instruction received by the receiving
unit 103, while the light-shielding gate is open. Here, the time
when light-shielding gate is closed is not related to the change
of the exposure time. As a result, the light-shielding unit 101
closes the light-shielding gate when the exposure time is elapsed,
and blocks the light incident on all the unit cells at the same
time.
[0087] After the light-shielding unit 101 closes the light-shielding
gate, the reading unit 105 sequentially reads the pieces of the
luminance information for still pictures from the unit cells, while
the light-shielding gate is closed.
[0088] After the reading unit 105 finishes reading the luminance
information for still pictures, the light-shielding unit 101 opens
the light-shielding gate, and prepares for the restart of the operation
for displaying moving pictures, which is performed by the monitor
unit 102.
[0089] After the luminance information for still pictures is read
and the light-shielding unit is closed, the monitor unit 102 restarts
the operation for displaying moving pictures.
<Operations>
[0090] FIG. 9 shows a processing procedure performed by the digital
camera 100 according to the first embodiment to take a still picture.
[0091] FIG. 10 is an example timing chart for control pulses and
so on used in the digital camera 100 according to the first embodiment.
[0092] The following describes the processing procedure for taking
a still picture with reference to FIG. 9 and FIG. 10.
[0093] (1) The drive control device 30 judges whether the main
switch has been pressed (Step S1).
[0094] Here, assume that the light-shielding gate (a mechanical
shutter) of the light-shielding unit 101 has been open in the stopped
state before the main switch is pressed.
[0095] (2) If the main switch has been pressed, the state is changed
to the moving pictures displaying state (state in the period before
the time T1 in FIG. 10), and the monitor unit 102 sequentially reads
pieces of the luminance information and display the luminance information
as moving pictures, while the mechanical shutter is open (Step S2).
[0096] (3) While the state is moving picture displaying state,
the receiving unit 103 waits for the shooting instruction (T1) (Step
S3). Here, assume that the receiving unit 103 waits for the shutter
button to be pressed.
[0097] (4) If the shutter button is pressed by the user, the receiving
unit 103 instructs the monitor unit 102 to stop operations for displaying
moving pictures. The monitor unit 102 stops the start pulse used
for reading image signals once (T2) after the shutter button is
pressed, and then stops the start pulse used for the electronic
shutter twice (T3 and T4) (Step S4).
[0098] (5) The receiving unit 103 sets T6 as a time at which the
mechanical shutter is closed. T6 is a little before T5 at which
the start pulse used for reading image signals is restarted (Step
S5).
[0099] (6) The receiving unit 103 sets T7 as a possible start point
of the all-reset pulse. T7 is a time at which the operation of the
mechanical shutter in accordance with the start pulse used for the
electronic shutter finishes. Then, the receiving unit 103 sets T6
as a possible end point of the application of the all-reset pulse.
T6 is a time at which the mechanical shutter is closed (Step-S6).
[0100] (7) The receiving unit 103 determines the application timing
of the all-reset pulse (T8) based on the possible end point, with
consideration of the exposure time (Step S7).
[0101] (8) The all-reset unit 104 applies the all-reset pulse at
T8 in accordance with the decision by the receiving unit 103, to
reset all the pieces of the luminance information stored in the
unit cells at the same time (Step S8).
[0102] (9) The drive control unit 30 applies the mechanical shutter
driving pulse at T6 in accordance with the decision by the receiving
unit 103, and the light-shielding unit 101 closes the mechanical
shutter (Step S9).
[0103] (10) The drive control unit 30 applies the start pulse used
for reading image signals at T5, and still picture data is output
(Step S10).
[0104] (11) As the still picture data is output, the drive control
unit 30 stops the mechanical shutter driving pulse (T9). Accordingly,
the light-shielding unit 101 opens the mechanical shutter. Then,
the operation for displaying moving pictures is restarted (Step
S11).
[0105] Note that the exposure time should be the same for each
pixel during the period from the time when the all-reset unit 104
resets all the pieces of the luminance information stored in unit
cells to the time when the light-shielding unit 101 closes mechanical
shutter. Accordingly, TROUT should be kept at "Low" during
the above-described period.
[0106] To keep TROUT at "LOW", two methods can be used.
The first method is to stop the pixel reading pulse used for the
electronic shutter (ETRANS) and the pixel reading pulse used for
reading image signals (TRANS). The second method is to stop the
SR output used for reading and the SR output used for the electronic
shutter. (Here, "to stop the pulse" means "to keep
the pulse at LOW".) If the shift register is structured by
a single channel MOS, a dynamic circuit is often used, and if this
is the case, misoperation tends to occur due to the floating status.
In this case, the first method, which stops the pixel reading pulse
used for the electronic shutter (ETRANS) and the pixel reading pulse
used for reading image signals (TRANS), is very effective, because
the TROUT can be kept at "LOW" even if the SR output used
for reading and the SR output used for the electronic shutter cause
misoperation.
[0107] Also, to suppress a leak caused due to change in potential
in a floating fusion unit (an FD unit), from which to read the luminance
information, it is preferable to keep the RSOUT at "LOW"
during the exposure.
[0108] Here, to keep the RSOUT at "LOW" two methods can
be used. The first method is to stop the pixel reset pulse used
for the electronic shutter (ERSCELL) and the pixel reset pulse used
for reading image signals (RSCELL). The second method is to stop
the SR output used for reading and the SR output used for the electronic
shutter. (Here, "to stop the pulse" means "to keep
the pulse at LOW".)
[0109] For the same reason as in the case of the TROUT, the first
method, which stops the pixel reset pulse used for the electronic
shutter (ERSCELL) and the pixel reset pulse used for reading image
signals (RSCELL), is very effective.
[0110] At the still picture shooting, in the case of not stopping
the pixel reset pulse used for the electronic shutter (ERSCELL),
the all-reset unit 104 should not apply the pixel reset pulse used
for the electronic shutter (ERSCELL) during the horizontal blanking
period to prevent conflict with the ERSCELL for moving picture.
However, in the case of stopping the pixel reset pulse used for
the electronic shutter (ERSCELL), the all-reset unit 104 can apply
the pixel reset pulse used for the electronic shutter (ERSCELL)
at any time in one cycle of the horizontal scanning, regardless
of whether the time is within the horizontal blanking period. Therefore,
it is preferable to stop the pixel reset pulse used for the electronic
shutter (ERSCELL).
[0111] FIG. 11 and FIG. 12 are example timing charts for control
pulses and so on used in the digital camera 100 according to the
first embodiment. FIG. 11 is different from FIG. 10 in that the
pixel reading pulse used for reading image signals (TRANS), the
pixel reset pulse used for reading image signals (RSCELL), the pixel
reading pulse used for the electronic shutter (ETRANS) and the pixel
reset pulse used for the electronic shutter (ERSCELL) are applied
during the horizontal blanking period as well.
[0112] As FIG. 11 shows, the pixel reading pulse used for reading
image signals (TRANS), the pixel reset pulse used for reading image
signals (RSCELL), the pixel reading pulse used for the electronic
shutter (ETRANS) and the pixel reset pulse used for the electronic
shutter (ERSCELL) may be applied during the horizontal blanking
period as well.
[0113] FIG. 12 is different from FIG. 11 in that, at the still
picture shooting, only the pixel reading pulse used for the image
signals (TRANS) and the pixel reading pulse used for the electronic
shutter (ETRANS) are stopped, and the pixel reset pulse used for
the electronic shutter (ERSCELL) is stopped only during the resetting
period of the all reset unit 104.
[0114] AS FIG. 12 shows, it is not necessary to stop the pixel
reset pulse used for reading image signals (RSCELL). The pixel reset
pulse used for the electronic shutter (ERSCELL) should be stopped
at least during the resetting period.
[0115] The ideal application timing of the control pulses and so
on is the timing illustrated in FIG. 10. However, the timing illustrated
in FIG. 11 has the advantage that it can simplify the control, and
the timing illustrated in FIG. 12 can further simplify the control.
Therefore, it is possible to use any of them according to the purpose.
<Summary>
[0116] As described above, according to the first embodiment of
the present invention, although the pieces of the luminance information
are read from the unit cells at different times, all the unit cells
are exposed exactly at the same time.
[0117] Accordingly, the present invention is capable of preventing
a distortion of an image caused due to the difference of the exposure
timing. In particular, the present invention can obtain a high-quality
image at the still picture shooting.
[0118] Also, the first embodiment of the present invention is capable
of preventing misoperation of a dynamic circuit using a single channel
MOS.
The First Modification
<Overview>
[0119] The first modification of the present invention is an example
in which the display of the moving pictures is stopped for a longer
period than the first embodiment, and accordingly the exposure time
for a still picture is longer than the first embodiment.
<Operations>
[0120] FIG. 13 shows the processing procedure performed to take
a still picture according to the first modification of the present
invention. FIG. 14 is a timing chart for control pulses and so on
according to the first modification.
[0121] The following describe the processing procedure performed
to take a still picture, with reference to FIG. 13 and FIG. 14.
[0122] Note that the same steps as the first embodiment are numbered
in the same manner, and such steps are not described here.
[0123] (1) to (3): The same as (1) to (3) of the first embodiment
(Steps 1 to 3).
[0124] (4) If the shutter button is pressed by the user, the receiving
unit 103 instructs the monitor unit 102 to stop operations for the
display of moving pictures. The monitor unit 102 stops the start
pulse used for reading image signals twice (T2 and T3) after the
shutter button is pressed, and then stops the start pulse used for
the electronic shutter three times (T4, T5 and T6) (Step S21).
[0125] (5) The receiving unit 103 sets T8 as a time at which the
mechanical shutter is closed. T8 is a little before T7 at which
the start pulse used for reading image signals is restarted (Step
S22).
[0126] (6) The receiving unit 103 sets T9 as a possible start point
of the application of the all-reset pulse. At T7, the mechanical
shutter finishes the operation in accordance with the start pulse
used for the electronic shutter. Then, the receiving unit 103 sets
T8 as a possible end point of the application of the all-reset pulse.
At T8, the mechanical shutter is closed (Step S23).
[0127] (7) The receiving unit 103 determines the application timing
of the all-reset pulse (T10) based on the possible end point, with
consideration of the exposure time (Step S24).
[0128] (8) The all-reset unit 104 applies the all-reset pulse at
T10 in accordance with the decision by the receiving unit 103, to
reset all the pieces of the luminance information stored in the
unit cells at the same time (Step S25).
[0129] (9) The drive control unit 30 applies the mechanical shutter
driving pulse at T8 in accordance with the decision by the receiving
unit 103, and the light-shielding unit 101 closes the mechanical
shutter (Step S26).
[0130] (10) The drive control unit 30 applies the start pulse used
for reading image signals at T7, and still picture data is output
(Step S27).
[0131] (11) As the still picture data is output, the drive control
unit 30 stops the mechanical shutter driving pulse (T11). Accordingly,
the light-shielding unit 101 opens the mechanical shutter. Then,
the operation for displaying moving pictures is restarted (Step
S28).
<Summary>
[0132] As described above, in the first modification of the present
invention, the exposure time for still picture shooting is longer
than that in the first embodiment. This is because the period, in
which the operations for displaying moving pictures is stopped for
shooting a still picture, is for three frames in the first modification,
whereas it is for two frames in the first embodiment. Accordingly,
for instance, it becomes possible to choose a narrow aperture, and
this gives a lot of options to the user at the picture shooting.
[0133] Note that the length of the period for stopping the operations
is not limited to three-frame long. The advantageous effect of the
present invention can be obtained regardless of the length (number
of frames) of the period.
The Second Modification
<Overview>
[0134] The second modification of the present invention describes
operations by which moving pictures are recorded using a pixel-skipping
mode which reduces the number of pixels, and still pictures are
recorded using a full-scan mode which uses all the pixels.
<Operations>
[0135] FIG. 15 shows a processing procedure performed to take a
still picture according to the second modification.
[0136] FIG. 16 is a timing chart for control pulses and so on according
to the second modification.
[0137] Note that the same steps as the first embodiment are numbered
in the same manner, and such steps are not described here.
[0138] (1) to (3): The same as (1) to (3) of the first embodiment
(Steps 1 to 3).
[0139] Here, the moving pictures are displayed in the pixel-skipping
mode, and the reading period is reduced toe approximately a half.
[0140] (4) The same as (4) of the first embodiment (Step S4).
[0141] (5) At T2, the mode is changed from the pixel-skipping mode
to the full-scan mode (Step S31).
[0142] (6) to (12): The same as (5) to (11) of the first embodiment
(Steps S5 to S11).
[0143] (13) At T9, the mode is changed from the full-scan mode
to the pixel-skipping mode (Step S32).
<Summary>
[0144] In the same manner as the first embodiment, according to
the second modification, high-quality images can be obtained especially
in the case of the still picture shooting, even in the case where
one of the pixel-skipping mode and the full-scan mode is chosen
based on the purpose. For instance, it becomes possible to obtain
high-resolution still pictures.
[0145] Note that the pixel skipping in the pixel-skipping mode
does not necessarily reduce the number of pixels to approximately
a quarter of the original and shorten the length of the period to
approximately a half of the original. The advantageous effect of
the present invention can be obtained regardless of the number of
the pixels and the length of the period.
The Third Modification
<Overview>
[0146] In the third modification of the present invention, the
all-reset pulse is applied out of the horizontal blanking period
for moving pictures. Accordingly, the all-reset pulse can be applied
more freely in view of the timing, compared to the first embodiment.
<Operations>
[0147] FIG. 17 is a timing chart for the all-reset pulse and so
on according to the third modification.
[0148] As FIG. 17 shows, the all-reset pulse is applied at a time
out of the horizontal blanking period. Accordingly, it becomes possible
to drive the electronic shutter at any time out of the horizontal
blanking period.
<Summary>
[0149] As described above, the all-reset pulse can be applied more
freely in view of the timing, compared to the first embodiment.
[0150] Note that the present invention may be a combination among
any of the first embodiment and the first to third modifications.
Also, the present invention may include functions of any of the
first embodiment and the first to third modifications as switchable
functions.
INDUSTRIAL APPLICABILITY
[0151] The present invention is applicable to imaging apparatuses
such as video cameras and digital still cameras. Although not reading
luminance information from all the unit cells at the same time,
the solid-state imaging device according to the present invention
is capable of completely eliminating the distortion of the image
caused by the difference of exposure timing. Also the present invention
contributes to improve the quality of the image taken by imaging
devices with reduced power consumption. Therefore, the present invention
has a great deal of potential in industry.
[0152] Although the present invention has been fully described
by way of examples with reference to the accompanying drawings,
it is to be noted that various changes and modifications will be
apparent to those skilled in the art. Therefore, unless such changes
and modifications depart from the scope of the present invention,
they should be construed as being included therein.
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