Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1997-12-22
2002-09-17
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
C348S311000, C257S346000
Reexamination Certificate
active
06452634
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charge transfer device and a method of driving the same, and a solid-state imaging device and a method of driving the same.
2. Description of the Related Art
In recent years, higher quality cameras have been demanded in the field of an animation picture camera and a still picture camera.
Although, generally the number of picture elements of an imaging device is increased to raise the quality of such a picture, an increase of the number of picture elements delays a transfer rate upon frame transfer of a signal charge of the picture element or a so-called frame rate. Consequently, in an auto focus (AF: auto focus control) camera using output signals of an imaging device, an auto iris (AE, auto exposure control) camera, auto white balance (AWB) camera and the like, the feedback is delayed or it may be difficult to follow a motion of a camera or a movement of an object when a composition is determined while seeing an animation output in an electronic still camera.
FIG. 1
is a plan view of an example of a CCD imaging device
51
to be used in such a camera. This CCD imaging device
51
transfers a signal charge in a so-called inter-line transfer method. In this imaging device, a plurality of light receiving units
52
made of a photo sensor are arranged in a matrix configuration. Each column of the light receiving units
52
is connected to a vertical CCD register
54
through a reading gate portion
53
, and the vertical CCD registers
54
are connected to a horizontal CCD register
55
. Charges from the horizontal CCD register
55
are converted through an output circuit such as an amplifier
56
or the like a voltage and then outputted as an output voltage V
out
.
In the vertical ccD register
54
, vertical drive pulses &phgr;V
1
, &phgr;V
2
, &phgr;V
3
, &phgr;V
4
are applied to its transfer electrode and the signal charges are transferred in the 4-phase driving.
On the other hand, in the horizontal CCD register
55
, horizontal drive pulses &phgr;H
1
, &phgr;H
2
are applied alternately to the transfer electrodes arranged corresponding to each column of the respective light receiving unit and the signal charges are transferred in the 2-phase driving as described later.
To solve the above problem, that is, to raise the frame rate, it can be considered to increase the driving frequency of the CCD register of the CCD imaging device or the system. However, if the driving frequency is increased, its power consumption will resultantly increase.
In the CCD imaging device, a correlated double sampling (CDS) is carried out so as to cancel a reset noise or the like. If the driving frequency is raised, a necessity of carrying out the phase adjustment of sampling hold pulse in this sampling arises so that production efficiency drops.
As a means for making a horizontal scanning period half without increasing the data rate from the CCD imaging device, there are a method of adding two horizontal picture elements by floating diffusion (FD) by doubling the drive frequency of the horizontal CCD register and a method of adding two picture elements at the final stage by doubling the drive frequency of a stage other than the final stage of the horizontal CCD register. However, in any cases, the shape of output waveform is changed, so that the preset period or data period of the output waveform which can be sampled by the correlated double sampling or the like is reduced.
FIG. 2
shows a configuration of a 2-phase drive horizontal CCD register of the CCD imaging device
51
shown in FIG.
1
and its potential in the transfer direction.
FIG. 3
shows the drive pulses &phgr;H
1
, &phgr;H
2
and the CCD output waveform upon a normal operation of the horizontal CCD register.
In the horizontal CCD register
55
, as shown in
FIG. 2
, a plurality of transfer electrodes
57
comprising a storage electrode
57
s
made of multi-crystal silicone of a first layer, and a transfer electrode
57
t
made of multi-crystal silicone of a second layer are arranged on a semiconductor substrate through an insulation film in the electrode transfer direction so as to form a plurality of transfer portions. A first phase drive pulse &phgr;H
1
is applied to the transfer electrode
57
of every second transfer portion, and a second phase drive pulse &phgr;H
2
is applied to the transfer electrode
57
of every other transfer portion, so that the signal charge is transferred by a so-called 2-phase complementary drive.
That is, as shown in
FIG. 2
, at a time point T
1
, the first phase drive pulse &phgr;H
1
becomes a high level while the second phase drive pulse &phgr;H
2
becomes a low level, so that the potential of the transfer portion to which &phgr;H
1
is to be applied becomes deep and then a signal charge e is transferred thereto.
Next, at a time point T
2
, the first phase drive pulse &phgr;H
1
becomes a low level while the second phase drive pulse &phgr;H
2
becomes a high level, so that the potential of the transfer electrode portion to which &phgr;H
2
is to be applied becomes deep and hence the signal charge is transferred from the transfer portion to which &phgr;H
1
is to be applied to the transfer portion to which &phgr;H
2
is to be applied.
In this manner, the signal charges are successively transferred in the transfer direction by the 2-phase drive pulses &phgr;H
1
, &phgr;H
2
.
The transfer portion at the final stage of the horizontal CCD register
55
is so constructed that the first phase drive pulse &phgr;H
1
is applied thereto. At the time point T
2
, the signal charge is transferred from the horizontal CCD register
55
to the floating diffusion (FD) (not shown) and converted to a signal voltage.
After a signal is read through the floating diffusion (FD), a reset gate pulse &phgr;RG is applied to a reset gate portion adjacent to the floating diffusion (FD) so that the charge of the floating diffusion (FD) is reset.
Thus, a CCD output waveform shown in
FIG. 3
is obtained.
A portion Tp in the CCD output waveform is a section which indicates a preset signal and a portion therein Td is a section which indicates a data signal.
As for the output signal from the CCD imaging device, generally so as to improve an S/N ratio, first the correlated double sampling, that is, the preset signal Tp is clamped and then the data signal portion Td is sampled.
Meantime, if the number of picture elements is increased to improve the picture quality, a fetch speed of one picture screen, that is, a so-called frame rate is retarded, so that feedback of AF, AE, AWB or the like using the CCD output signal is delayed or it becomes difficult to display the same on a liquid crystal screen or the like to confirm its composition.
To improve such a defect, there is a method of doubling the drive frequency of, for example, the horizontal CCD register so as to quicken the output data rate.
FIG. 4
shows a horizontal drive pulse and a CCD output waveform of this case.
Because the drive frequency is doubled, the wavelengths of the horizontal drive pulse &phgr;H
1
, &phgr;H
2
and the reset gate pulse &phgr;RG become half respectively and the period of the CCD output waveform also becomes half.
However, in this case, widths Tp
2
, Td
2
of the portions for carrying out the clamp or sampling become half as compared to a usual case, so that the phase of a clamp pulse or sampling pulse needs to be adjusted one by one thereby reducing production efficiency.
Further, because the data rate doubles, the signal processing speed also doubles so that power consumption and noise increase. Further, because the system design is limited, disadvantage arises in production cost.
On the other hand, as a method of doubling the scanning speed of the horizontal CCD register without changing the data rate, there is a method of adding signal charge of two horizontal picture elements at the floating diffusion (FD).
FIG. 5
shows a horizontal drive pulse and a CCD output waveform of this case.
According to this method, the lengths of a preset period Tp
3
and a data
Ishigami Tomio
Nakagawa Shinji
Garber Wendy R.
Sonnenschein Nath & Rosenthal
Tilley Rashawn M.
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