Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1997-02-06
2001-04-03
Garber, Wendy (Department: 2712)
Television
Camera, system and detail
Solid-state image sensor
C348S314000
Reexamination Certificate
active
06211915
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to a solid-state imaging device, and more specifically, to a so-called “wide dynamic range CCD solid-state imaging device”, the dynamic range of which is wide with respect to a light input.
In CCD solid-state imaging devices, light receiving portions (pixels) are arranged in a two-dimensional matrix form, and photoelectrically converts input light into signal charges, and stores the signal charges. After these signal charges are overflown from the light receiving portions, since the signal outputs based on the overflown signal charges become constant, such a signal output can be hardly obtained which corresponds to incident light amounts exceeding the saturation level of the light receiving portions. As a result, dynamic ranges in response to the light inputs would become narrow.
To extend, or enlarge this narrow dynamic range, there is one conventional solid-state imaging apparatus described in, for instance, Japanese Laid-open Patent Application No. 3-117281. That is, as shown in
FIG. 1
, two different sorts of light receiving portions having different sensitivities are alternately arranged adjacent to each other. For instance, the high-sensitive light receiving portion
101
and the low-sensitive light receiving portion
102
are alternately arranged adjacent to each other along the vertical direction. The signal charges of the high-sensitive light receiving portion
101
are limited in the light receiving portion and thereafter the limited signal charges are read out from the vertical transfer register
103
. After the signal charges of the high-sensitive light receiving portion
101
are mixed with the signal charges of the low-sensitive light receiving portion
102
in this register
103
, the mixed signal charges are vertically transferred. Furthermore, the signal charges are horizontally transferred by the horizontal transfer register
104
to the charge detecting portion
105
. The horizontally transferred signal charges are converted into the electric signals in this charge detecting portion
105
, and thereafter the electric signals are outputted via the buffer
106
.
In this CCD solid-state imaging device, when the incident light amount exceeds a predetermined amount, since the limiter is operable to the signal charges of the high-sensitive light receiving portion
101
, the signal charges of the high-sensitive light receiving portion
101
are mixed with the signal charges of the low-sensitive light receiving portion
102
to thereby achieve such an input/output characteristic approximated to a bent line shown in FIG.
2
. As a result, a wide dynamic range may be realized. It should be noted that in the graphic representation of
FIG. 2
, a dot and dash line shows the input/output characteristic of the high-sensitive light receiving portion
101
, a dotted line indicates the input/output characteristic of the low-sensitive light receiving portion
102
, and a solid line represents the input/output characteristic of the mixed signal charges.
However, in the conventional CCD solid-state imaging device with the above-described structure, i.e., the limiters are operated for the respective light receiving portions in the high-sensitive light receiving portion
101
, the overflow characteristics are fluctuated in the respective light receiving portions, and since the fluctuations in the saturated charge amounts “Qs” of the respective light receiving portions become large, offsets are produced in the input/output characteristic approximated to the folded line, as shown in FIG.
3
. As a result, when a large light amount is entered under which the high-sensitive light receiving portion
101
becomes saturated, there are large fluctuations in the saturated charge amounts “Qs” of the respective light receiving portions. Thus, there is a problem that fixed pattern noise is produced in the images (namely, fluctuation of fixed patterns).
SUMMARY OF THE INVENTION
Therefore, the present invention has an object to provide a solid-state imaging device capable of enlarging a dynamic range without producing fixed pattern noise caused by fluctuations in saturated charge amounts “Qs” of the respective light receiving portions.
A solid-state imaging apparatus, according to the present invention, is arranged by comprising an imaging portion for obtaining more than two sorts of signal charges with different sensitivities; a charge transferring portion for transferring the signal charges having the different sensitivities transferred from this imaging portion as point sequential signals; a bias applying circuit for applying a DC bias voltage to an output gate of the charge transferring portion, said DC bias voltage being used to clip at least signal charges other than a signal charge having a minimum sensitivity in a preselected clip level; and a charge detecting portion for mixing the signal charge clipped by the output gate with the signal charges having other sensitivities to be converted into an electric signal.
In the solid-state imaging device with the above-described arrangement, when more than two sorts of signal charges having the different sensitivities are transferred from the imaging portion to the charge transferring portion, the charge transferring portion transfers these signal charges having the different sensitivities in such a manner that these signal charges become point sequential signals. In this charge transfer portion, since the DC bias voltage corresponding to a predetermined clip level is applied to this output gate, when a large amount of light is entered, the signal charge having the high sensitivity exceeds this clip level to be therefore clipped. Thereafter, the clipped signal charge is supplied to the charge detecting portion. The charge detecting portion mixes this clipped signal charge with the signal charges with other sensitivities to convert the mixed signal charges into an electric signal.
REFERENCES:
patent: 4875098 (1989-10-01), Yamamoto et al.
patent: 5239192 (1993-08-01), Hirota
patent: 5335075 (1994-08-01), Komiya et al.
patent: 5572256 (1996-11-01), Egawa et al.
patent: 1-254893 (1989-09-01), None
patent: 3-117281 (1989-09-01), None
Garber Wendy
Sonnenschein Nath & Rosenthal
Sony Corporation
Wilson Jacqueline
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