Imaging apparatus

Details Imaging apparatus Imaging apparatus

1999-07-09

2004-03-02

Garber, Wendy R. (Department: 2612)

Television

Camera, system and detail

Solid-state image sensor

C348S372000

Reexamination Certificate

active

06700610

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to imaging apparatus having an imaging element, which are used for electronic still cameras, digital cameras and the like.
BACKGROUND OF THE INVENTION
Hitherto, various imaging elements applicable to such imaging apparatuses have been proposed. Among such imaging elements is an inter-line CCD solid-state imaging element having a vertical overflow drain structure as schematically shown in FIG.
15
.
The CCD shown in
FIG. 15
comprises a two-dimensional array of photo-diodes
1
arranged in both horizontal and vertical directions and each constituting a photo-electric converting cell for accumulating charge according to light incidence, a plurality of vertical shift registers
3
constituting vertical shift paths for receiving charge accumulated in associated photo-diodes
1
via a transfer gate
2
and progressively vertically shifting the received charge, a horizontal shift register
4
constituting a horizontal shift path for receiving shifted charge from the vertical shift registers
3
and progressively horizontally shifting the received charge, and a signal detector
5
for amplifying the output signal of the horizontal shift register
4
and outputting the amplified signal.
FIG. 16
is a block diagram showing the basic construction of an imaging apparatus with the CCD shown in FIG.
15
. The illustrated imaging apparatus comprises a focusing lens
11
, a shutter means
12
, a CCD
13
, a signal processor
14
, a shutter driver
16
, a signal generator
17
, a CPU
18
, a lens stop means
20
, a recording means
21
and a lens stop driver
22
. The focusing lens
11
focuses a light beam of a scene on a light incidence surface of the CCD
13
. The lens stop means
20
stops or reduces the area of the light flux of the scene from the lens
11
. The shutter means
12
is constituted by, for instance, a mechanical shutter for either passing or blocking the scene light flux. The CCD
13
converts the scene light beam flux having passed through the shutter means
12
to an electric signal. The signal processor
14
performs various processes on the electric signal from the CCD
13
and outputs an image signal thus generated. The recording means
21
has a DRAM for storing the image signal from the signal processor
14
as a still image or a recording medium on which the compressed image signal is recorded as a still image. The shutter driver
16
controls the shutter means
12
. The lens stop driver
22
controls the lens stop means
20
. The signal generator
17
supplies pulses for controlling the period of charge accumulation in the photo-diodes
1
, pulses for driving the vertical shift registers
3
and pulses for driving the horizontal shift register
4
to the CCD
13
and also supplies pulses for driving the signal processor
14
in synchronism with the CCD
13
. The CPU
18
collectively controls circuits including the signal generator
17
and the lens stop driver
22
. The signal processor
14
and the signal generator
17
together constitute a digital signal processor (DSP)
19
.
FIG. 17
is a timing chart illustrating a conventional imaging operation in the imaging apparatus shown in FIG.
16
. Specifically,
FIG. 17
shows a vertical sync signal VD, a transfer gate pulse train TG, a sub-pulse train SUB, a vertical shift register shift pulse train VT, a clamp pulse train CLP, opening/closing operation of the shutter means
12
, operations of the lens stop means
20
and the lens stop driver means
22
and a CCD signal, i.e., a signal read out from the CCD
13
.
The vertical sync signal VD is a pulse train prescribing a predetermined unit period of time for obtaining a signal representing one image (i.e., one frame image). Here, periods prescribed by the individual pulses are labeled V
1
, V
2
, . . . .
The transfer gate pulse train TG consists of pulses for determining the timing of the transfer of charge stored in the photo-diodes
1
to the vertical shift registers
3
, and is applied to the transfer gate
2
in synchronism with the vertical sync signal VD. The transfer gate pulses TG corresponding to the periods V
1
, V
2
, . . . of the vertical sync signal VD are labeled TG
0
, TG
1
, . . . .
The sub-pulse train SUB consists of pulses for discharging charge generated in the photo-diodes
1
in the vertical direction of the substrate. The discharge of charge is done while sub-pulses SUB are outputted. That is, the charge is accumulated in the photo-diodes
1
during periods tb
1
, tb
2
, . . . , in which the sub-pulses SUB are stopped in the periods V
1
, V
2
, . . . of the vertical sync signal VD. Thus, it will be seen that a so-called electron (or element) shutter is realized, in which the effective exposure time is controlled through control of the charge accumulation period. The charge accumulation time is determined as a result of measurement of light of the scene image with a measuring means (not shown), and it is measured by counting sub-pulses SUB.
The vertical shift register shift pulse train VT consists of pulses for causing progressive shift of charge in the vertical shift registers
3
toward the horizontal shift register
4
.
The clamp pin CLP consists of pulses for clamping portions of the CCD signal corresponding to optical black portion of the CCD. By the clamping, the potential level of the image signal is stabilized to hold a stable black level.
The shutter means
12
is normally open, and is closed (light-shuttered or -blocked) when causing the transfer of charge accumulated in the photo-diodes
1
in response to a recording trigger signal. As the recording trigger signal, in the case of a shutter release button (not shown) providing a two-stage trigger signal, that is, in the case when a first trigger pulse is generated in a preparatory stage of lightly depressing the shutter release button for recording and a second trigger pulse is generated by further depressing the shutter release button for starting the recording of a still image, the second trigger pulse corresponds to the recording trigger signal.
The CCD signal has time sections to
1
and to
2
corresponding to optical black portions in the vertical direction and an effective time section intervening as a scene image period between these time sections. Normally the optical black signal is at a higher level than the effective period signal level.
The lens stop means
20
is normally in an open diameter state, in the case of such a bright scene that normal exposure will be exceeded with the sole electronic shutter operation in its open diameter state, it is driven to stop the light flux.
As is seen from the timing chart of
FIG. 17
, in the prior art imaging apparatus, upon generation of a recording trigger signal in, for instance, the period V
3
, vertical shift register shift pulses VT are continuously outputted during a subsequent time section ta for fast sweep-out of unnecessary charge in the vertical shift registers
3
, while steadily applying shift pulses without any pause period for the read-out. In the subsequent period V
4
, the charge is accumulated in the photo-diodes
1
by suspending the application of sub-pulses SUB for a time section tb
4
corresponding to the exposure period, which has been determined by a light measurement process executed on the basis of the CCD signal until the recording trigger signal generation. At this time, appropriate exposure may not be ensured with the sole electronic shutter operation. In such a case, in synchronism with the start of the period V
4
the lens stop driver
22
is turned on to cause the lens stop means
20
to stop or decrease the diameter of the scene light flux. At any rate, the time section tb
4
constitutes an exposure time for one frame image.
In the subsequent period V
5
, the image obtained by the exposure during the time section tb
4
in the period V
4
is outputted as signal CCD
4
, which is outputted as a result of the exposure in response to the recording trigger signal from the signal amplifier
5
. Also, in synchronism with the start of the period V
5
the lens

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