Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1998-03-09
2004-10-05
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
C348S302000, C348S308000, C348S312000, C250S208100
Reexamination Certificate
active
06801253
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid-state image sensor and a method of driving the same, and more particularly to an amplifying type solid-state imaging device such as a MOS image sensor where unit pixels each having an amplifying function are arrayed in the form of a matrix of rows and columns, and also to a method of driving such an image sensor.
2. Description of the Related Art
FIG. 13
shows an exemplary structure of a conventional amplifying type solid-state image sensor known heretofore in the related art. In this diagram, a unit pixel
106
is composed of a photodiode
101
, an FD (floating diffusion) read MOS transistor
102
, an FD amp MOS transistor
103
, an FD reset MOS transistor
104
, and a vertical select MOS transistor
105
. In this structure, a gate electrode of the FD read MOS transistor
102
is connected to a vertical read line
107
, a gate electrode of the FD reset MOS transistor
104
to a vertical reset line
108
, a gate electrode of the vertical select MOS transistor
105
to a vertical select line
109
, and a source electrode of the vertical select MOS transistor
105
to a vertical signal line
110
, respectively.
A horizontal select MOS transistor
112
is connected between one end of the vertical signal line
110
and a horizontal signal line
111
. The operation of each pixel is controlled per row by three kinds of vertical scanning pulses &phgr;VS
n
, &phgr;VT
n
, and &phgr;VR
n
, outputted from a row-select vertical scanning circuit
113
, and a pixel signal is outputted to the horizontal signal line
111
via the horizontal select MOS transistor
112
which is controlled by a horizontal scanning pulse &phgr;H
m
outputted from a column-select horizontal scanning circuit
114
. At this time, the signal charge stored in the photodiode
101
through photoelectric conversion is converted into a signal current by the FD amp MOS transistor
103
and then is delivered as an output signal of the image sensor.
However, in the known amplifying type solid-state image sensor of the above structure, there exists a problem of characteristic deviation in the active elements constituting each pixel, principally in the FD amp MOS transistor
103
, and particularly relative to deviation of the threshold voltage Vth of the MOS transistor. And such deviation is included directly in the output signal of the image sensor. Since this characteristic deviation has a fixed value per pixel, it appears as a fixed pattern noise (FPN) in the picture displayed on a screen. For suppressing such fixed pattern noise, it is necessary to externally connect to the device a noise elimination circuit using a frame memory or a line memory, so as to eliminate any noise component derived from the characteristic deviation in the pixel. As a result, the scale of the camera system is rendered larger correspondingly to the noise elimination circuit connected thereto externally.
In comparison with the above, there is contrived another amplifying type solid-state image sensor which has a structure of FIG.
14
and is capable of internally suppressing such fixed pattern noise in the device. The difference of this solid-state image sensor resides in the point that, although its unit pixel
106
is structurally the same as
FIG. 13
, a horizontal output circuit
115
is provided for suppressing the fixed pattern noise derived from the characteristic deviation in the pixel
106
, and this horizontal output circuit
115
executes a process of taking the difference between pre-read and post-read (pre-reset and post-reset) signals of the pixel
106
.
In
FIG. 14
, a load MOS transistor
116
serving as a load to the source follower operation of an FD amp MOS transistor
103
is connected between a vertical signal line
110
and the ground. Further, one main electrode of each of paired signal switch MOS transistors
117
and
117
′ is connected to the vertical signal line
110
. And a pair of signal holding capacitors
118
and
118
′ are connected respectively between the ground and the other main electrodes of such paired signal switch MOS transistors
117
and
117
′.
Further a pair of horizontal select MOS transistors
112
and
112
′ are connected respectively between the other main electrodes of the paired signal switch MOS transistors
117
,
117
′ and a pair of horizontal signal lines
111
,
111
′. And a noninverting (+) input terminal and an inverting (−) input terminal of a differential amplifier
119
are connected respectively to the pair of horizontal signal lines
111
and
111
′.
In the amplifying type solid-state image sensor of the above structure, pixel pre-reset and post-reset signals are held respectively in signal holding capacitors
118
,
118
′ via the signal switch MOS transistors
117
,
117
′ and then are supplied to the differential amplifier
119
via the horizontal select MOS transistors
112
,
112
′ and the horizontal signal lines
111
,
111
′. Subsequently, the difference between the pixel pre-reset and post-reset signals is taken in the differential amplifier
119
to thereby eliminate the fixed pattern noise derived from the characteristic deviation in each unit pixel.
Although it is possible in the amplifying type solid-state image sensor of the above structure to suppress the fixed pattern noise derived from the characteristic deviation in each unit pixel, the pixel pre-reset and post-reset signals reach the differential amplifier
119
via separate signal paths, so that the characteristic deviations relative to the paired signal switch MOS transistors
117
,
117
′ and the paired horizontal select MOS transistors
112
,
112
′ appear in the picture as fixed pattern noises with vertically correlated streaks. Therefore, this structure also requires an external correction circuit for suppressing the fixed pattern noises with vertical streaks.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved amplifying type solid-state image sensor which is capable of suppressing, within the device, any fixed pattern noise derived from characteristic deviation in each unit pixel and also other fixed pattern noise of vertical streaks.
And another object of the invention is to provide a method of driving such an image sensor.
According to one aspect of this invention, there is provided a solid-state image sensor which comprises, in each of unit pixels arrayed to form a matrix of rows and columns, a photoelectric conversion element, an amplifying element having a storage to store a signal charge transferred thereto from the photoelectric conversion element and serving to convert the signal charge of the storage into an electric signal, and a selector switch for selectively outputting the pixel signal from the amplifying element to a vertical signal line. The image sensor further comprises, in each of the unit pixels, a reset circuit for resetting the storage of each amplifying element every time a pixel signal is outputted from each unit pixel.
According to another aspect of this invention, there is provided a method of driving a solid-state image sensor having the above structure. The method comprises the steps of resetting the storage of each amplifying element every time a pixel signal is outputted from each of the unit pixels; then delivering a pre-reset signal and a post-reset signal from each unit pixel and transferring such signals via a common transfer path; and taking the difference between the pre-reset signal and the post-reset signal.
In each of the unit pixels constituting the solid-state image sensor of the structure described above, the storage of each amplifying element is reset every time a pixel signal is outputted, so that a pre-reset signal and a post-reset signal per pixel are outputted successively from each of the unit pixels. In this case, fixed pattern noise derived from any characteristic deviation in the pixel is generated as an offset component from the amplifying el
Suzuki Ryoji
Yonemoto Kazuya
Sonnenschein Nath & Rosenthal LLP
Ye Lin
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