Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1999-09-29
2002-01-29
Garber, Wendy R. (Department: 2712)
Television
Camera, system and detail
Solid-state image sensor
C348S308000, C348S230100, C348S241000
Reexamination Certificate
active
06342920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoelectric conversion device, for example, to one-dimensional or two-dimensional photoelectric conversion devices for reading images in a video camera, X-ray imaging apparatus, infrared ray imaging apparatus, and the like and, more particularly, to a photoelectric conversion device using a skimming charge transfer scheme.
2. Related Background Art
Conventionally, CCDs are popularly used as imaging devices of video cameras, digital cameras, and the like, and such image reading device uses a “charge skimming transfer scheme” disclosed in, e.g., IEEE trans. Electron. vol. ED-29, p. 3, 1982 and Japanese Patent Publication No. 7-48826.
FIG. 13
shows an infrared ray imaging apparatus using the conventional charge skimming transfer scheme described in Japanese Patent Publication No. 7-48826.
FIGS. 12A and 12B
show changes in charge amount before and after charge skimming transfer, and
FIGS. 11A
to
11
C show the input circuit of a charge skimming transfer type infrared ray imaging element.
FIGS. 11A
to
11
C and
FIG. 13
illustrate a photodiode
101
, a silicon CCD
102
, infrared rays
104
, an output circuit
105
, an input gate electrode
110
, an accumulation electrode
111
, a skimming electrode
112
, a CCD electrode
113
, an overflow drain
114
, an overflow electrode
115
, and a skimming voltage input terminal
119
.
In
FIGS. 12A and 12B
, charges
116
are produced due to background radiation, charges
117
are ascribed to radiation from a signal source, and charges are skimmed at a skimming level
118
.
The operation of the charge skimming transfer type infrared ray imaging element with the above arrangement will be described below with reference to the drawings.
(1) As shown in
FIG. 11A
, infrared rays
104
are converted into photocurrents by the photodiode
101
, and the photocurrents are input to and accumulated in a portion beneath the accumulation electrode
111
via the input gate electrode
110
.
(2) Upon completion of accumulation, as shown in
FIG. 11B
, a pulse signal is applied to the skimming electrode
112
to change the height of the potential well to transfer some accumulated charges to a portion underneath the CCD electrode
113
. The amount of charges to be transferred is controlled by the pulse signal (to be referred to as a skimming voltage hereinafter) to be applied to the skimming electrode
112
.
(3) Thereafter, as shown in
FIG. 11C
, charges remaining in the portion beneath the accumulation electrode
111
are ejected to the overflow drain
114
via the overflow electrode
115
.
When charge skimming transfer is performed, as described above, since DC components
116
produced by the background radiation can be removed, as shown in
FIGS. 12A and 12B
, contrast can be emphasized, and the amount of charges to be transferred to the portion beneath the CCD electrode
113
can be reduced.
Charges transferred to the portion below the CCD electrode
113
are sequentially transferred by the CCD
102
in the same manner as in a case wherein the charge skimming transfer scheme is not adopted, and are output to an external circuit via the output circuit
105
.
As described above, in the conventional photoelectric conversion device, when the number of photons of background radiation is extremely larger than the number of photons radiated by the signal source, the obtained signal has low contrast, and such problem cannot be solved by merely extending the accumulation time of the silicon CCD. In the above-mentioned prior art, this problem is solved by performing skimming charge transfer. However, since the skimming voltage is calculated and generated by an external circuit on the basis of the signal voltages of the respective pixels, other problems such as a long processing time, high cost of the entire system, and the like are posed.
On the other hand, an X-Y address type photoelectric conversion device, which uses a CMOS sensor or the like in place of the CCD and comprises a charge skimming transfer means, has not reached practical application level yet.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an element comprising-a skimming charge transfer function in an X-Y address type photoelectric conversion device using, e.g., a CMOS sensor and having excellent characteristics.
It is an object of the present invention to provide a photoelectric conversion element and a control method therefor for transferring an optimum amount of photoelectric charge from a photoelectric conversion means and outputting a signal corresponding to the amount of photoelectric charge transferred.
In order to attain the above-described object,according to one aspect of the present invention, a photoelectric conversion device includes a plurality of pixels. Each pixel includes photoelectric conversion means for converting light into photoelectric charges, transfer means for transferring a portion of the photoelectric charges from the photoelectric conversion means, and reading means for non-destructively outputting a signal corresponding to the portion of the photoelectric charges transferred by the transfer means. The photoelectric conversion device further includes controlling means for controlling an amount of photoelectric charges transferred by the transfer means.
According to another aspect of the present invention, the controlling means includes pulse setting means for changing a pulse signal, and the controlling means controls the amount of photoelectric charges transferred in response to an output from the pulse setting means.
According to another aspect of the present invention, the controlling means controls an amount of photoelectric charge transferred based on the signal output by the reading means.
According to another aspect of the present invention, the controlling means controls the transfer means by a method that includes a first step of controlling the transfer means according to a first control signal and a second step of controlling the transfer means according to a second control signal that differs from the first control signal.
Other objects and features of the present invention will become apparent from the following description of the embodiments taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A
to
1
C are circuit diagrams showing a circuit for one pixel and a skimming charge transfer scheme according to the first embodiment of the present invention;
FIG. 2
is a circuit diagram of the first embodiment of the present invention;
FIG. 3
is a timing chart of the first embodiment of the present invention;
FIG. 4
is a flow chart showing the operation according to the first embodiment of the present invention;
FIG. 5
is a circuit diagram of an automatic skimming voltage control circuit according to the first embodiment of the present invention;
FIGS. 6A and 6B
are respectively a circuit diagram and a timing chart of a maximum value detection circuit for a pixel signal according to the first embodiment of the present invention;
FIG. 7
is a circuit diagram of the second embodiment of the present invention;
FIG. 8
is a circuit diagram of the third embodiment of the present invention;
FIG. 9
is a circuit diagram of a circuit for one pixel according to the fourth embodiment of the present invention;
FIG. 10
is a circuit diagram of a circuit for one pixel according to the fifth embodiment of the present invention;
FIGS. 11A
to
11
C are circuit diagrams for explaining the conventional charge skimming scheme;
FIGS. 12A and 12B
are graphs showing the relationship between the skimming operation and the charge amount; and
FIG. 13
is a circuit diagram for explaining the conventional charge skimming scheme.
REFERENCES:
patent: 4743959 (1988-05-01), Frederiksen
patent: 4866496 (1989-09-01), Audier
patent: 5003565 (1991-03-01), Yoshida
patent: 5146302 (1992-09-01), Kumada
patent: 5326996 (1994-07-01), McNutt
patent: 5345266 (1994-09-01), Denyer
patent: 5717199 (1998-02-01), Carbone et al.
p
Garber Wendy R.
Wilson Jacqueline
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