Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1998-09-28
2003-01-21
Vu, Ngoc-Yen (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
C348S314000, C348S320000
Reexamination Certificate
active
06509928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image pickup apparatus in which normal transfer of signal electric charges for a read operation and high-speed sweep transfer for a purge operation of useless electric charges are performed for a solid state image pickup device, and more particularly to an image pickup apparatus which can reduce a circuit scale.
2. Description of the Related Art
Hitherto, there is known an image pickup apparatus which includes a CCD image pickup device designed to perform normal transfer of signal electric charges for a read operation and high-speed sweep transfer for a purge operation of useless electric charges, and which is constructed as shown in FIG.
1
. The illustrated construction shows an electronic camera using a CCD image pickup device. In
FIG. 1
, denoted by reference numeral
1
is a lens,
2
is a CCD image pickup device,
3
is a signal processing circuit for processing an output signal of the CCD image pickup device
2
to form an image signal,
4
is a recording unit for recording the image signal from the signal processing circuit
3
,
5
is a signal generator for outputting drive signals, etc. to the components,
6
is a CPU for driving and controlling the components, and
7
is a release mechanism unit (including a record trigger for starting a recording operation) which is operated by an operator (photographer) for recording.
As one exemplified construction of the CCD image pickup device
2
shown in
FIG. 1
,
FIG. 2
shows a general construction of a CCD image pickup device
2
of vertical overflow drain/interline type. In
FIG. 2
, denoted by
11
is a photodiode constituting each of pixels which are arrayed two-dimensionally, and
12
is a transfer gate area for transferring signal electric charges accumulated in the photodiode
11
to a vertical shift register
13
. The signal electric charges transferred to the vertical shift register
13
are then transferred to a horizontal shift register
14
. The signal electric charges transferred to the horizontal shift register
14
are further transferred therein and delivered to an output terminal through a signal detector
15
.
The operation of the image pickup apparatus thus constructed will now be described with reference to a timing chart shown in FIG.
3
. In
FIG. 3
, VD represents a vertical synchronizing signal and HD represents a horizontal, synchronizing signal. Respective frame periods VD
1
, VD
2
, VD
3
, VD
4
and VD
5
are each set by the vertical synchronizing signal VD.
FIG. 3
shows the case where the record trigger for starting the recording operation is output in the frame period VD
2
. VSUB represents a pulse for purging out signal electric charges, which are accumulated in each photodiode of the CCD image pickup device, to the substrate side, i.e., a timing pulse for determining an exposure period of the CCD image pickup device. In the timing chart of VSUB, periods t
1
, t
2
, t
3
and t
4
each represent the exposure period during which electric charges are generated upon light entering the photodiode of the CCD image pickup device and accumulated therein, and hence during which VSUB is not output. The signal electric charges accumulated in the photodiode are transferred to the vertical shift register by a transfer pulse TG. Transfer pulses TG
1
, TG
2
, TG
3
and TG
4
are output respectively for each of the frame periods VD
1
, VD
2
, VD
3
and VD
4
. The signal electric charges transferred to the vertical shift register are then transferred successively by vertical transfer pulses V
1
, V
2
, V
3
and V
4
in four phases to the horizontal shift register. CLP represents a clamp pulse for stabilizing the image signal from the DC point of view. The clamp pulse CLP clamps a CCD signal output from the CCD image pickup device, thereby enabling the stable image signal to be supplied.
As shown in the timing chart of
FIG. 3
, when the record trigger is output during the frame period VD
2
to start the recording operation, an operation of discarding the electric charges, which are accumulated due to the exposure during the exposure period t
2
within the frame period VD
2
, as useless electric charges is first carried out. This useless charge purging operation is performed in a period t corresponding to the frame period VD
3
by a high-speed sweep using the vertical transfer pulses V
1
, V
2
, V
3
and V
4
. The reason why the high-speed sweep should be effected is as follows. When making exposure within the frame period VD
3
, if the signal electric charges accumulated in the exposure period within the preceding frame period VD
2
, a phenomenon called smear occurs and a normal image cannot be obtained. Practically, in the case of photographing an object of high brightness, the signal electric charges accumulated during the frame period VD
2
remain in the transfer line and are added to the signal electric charges generated due to the exposure within the frame period VD
3
, the resulting increased charges being output to as an CCD signal CCD
3
. To overcome such a problem, the above high-speed sweep operation must be performed so that the signal electric charges accumulated during the exposure period within the frame period VD
2
are all discarded out of a CCD output unit.
The frame period VD
3
in which the above high-speed sweep operation is performed is also an image pickup period requested by the record trigger, within which the photodiode of the CCD image pickup device is subjected to exposure during the exposure period t
2
and electric charges are accumulated in the photodiode. In the frame period VD
4
, the electric charges accumulated in the respective photodiodes are sequentially output as the CCD signal in the form of CCD
3
. Incidentally, the CCD signal has optical black areas t
ob1
and t
ob2
positioned at the head and tail, respectively, for determining a black level and an intermediate area t
O
provides an actual effective frame area.
FIGS. 4A and 4B
are timing charts for explaining the transfer timing for the normal read operation from the vertical shift register and the high-speed purging operation for purging out the useless electric charges transferred to the vertical shift register, respectively, in the above-described conventional image pickup apparatus. As shown in
FIG. 4A
, the transfer timing for the normal read operation is set by generating the vertical transfer pulses V
1
, V
2
, V
3
and V
4
in synchronism with the horizontal synch signal HD. On the other hand,
FIG. 4B
shows the timing at which the vertical transfer pulses are generated for purging out the useless electric charges at a high speed. In the high-speed sweep operation, the vertical transfer pulses are generated successively, as shown, so that the electric charges are swept away. Thus, the transfer operation for normal reading of the accumulated electric charges and the transfer operation for purging out the useless electric charges are different from each other in nature. In the conventional image pickup apparatus, therefore, transfer pulses are formed by separate circuits and supplied to the vertical shift register of the CCD image pickup device in a switching manner between the two transfer operations. However, forming the vertical transfer pulses for the normal read operation and the high-speed sweep operation by separate circuits raises the problem of increasing a circuit scale.
Also, when the vertical transfer pulses are generated at a certain pulse cycle successively for the high-speed sweep operation, there may occur a mismatch in timed relation between the vertical transfer pulses and the horizontal synchronizing signal HD within one horizontal period, as shown in
FIG. 4B
; hence a vertical transfer stop period t
v
may occur. This raises the problem that the timing of the vertical transfer pulses cannot be managed within each horizontal period and a circuit scale is necessarily increased because of a difficulty in timing control.
Further, in the conventional image pickup apparatus, the operation for sweeping a
Kijima Takayuki
Ogawa Yoshitaka
Sakurai Junzo
Yokouchi Masaki
Armstrong Westerman & Hattori, LLP
Olympus Optical Co,. Ltd.
Vu Ngoc-Yen
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