Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1998-08-14
2004-01-13
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
C348S302000
Reexamination Certificate
active
06677993
ABSTRACT:
BACKGROUND 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 having an amplifying function per unit pixel, and also to a method of driving such an image sensor.
FIG. 14
shows an exemplary structure of a conventional two-dimensional solid-state image sensor known heretofore as an amplifying type solid-state imaging device in the related art. In this diagram, a unit pixel
105
is composed of a photodiode
101
, an amplifying MOS transistor
102
, a photodiode reset MOS transistor
103
, and a vertical select MOS transistor
104
. In this structure, a gate electrode of the photodiode reset MOS transistor
103
is connected to a vertical reset line
108
, a gate electrode of the vertical select MOS transistor
104
to a vertical select line
109
, and a source electrode of the vertical select MOS transistor
104
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 two kinds of vertical scanning pulses øVSn and øVRn 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 øHm 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 amplifying MOS transistor
102
and then is delivered as an output signal of the image sensor.
However, in the known amplifying type two-dimensional 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 amplifying MOS transistor
102
, 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, in a camera system or the like employing such a solid-state image sensor as an imaging device, the scale thereof 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.
15
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
105
is structurally the same as
FIG. 14
, a horizontal output circuit
115
is provided for suppressing the fixed pattern noise derived from the characteristic deviation in the pixel
105
, 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
105
.
In
FIG. 15
, a load MOS transistor
116
serving as a load to the source follower operation of an amplifying MOS transistor
102
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 a first aspect of the invention, there is provided a solid-state image sensor which comprises unit pixels each having a photoelectric conversion element for converting incident light into electric signal charge and then storing the signal charge obtained through such photoelectric conversion, an amplifying element for converting into an electric signal the signal charge stored in the photoelectric conversion element, and a select switch for selectively outputting the pixel signal from the amplifying element to a signal line; and a reset circuit in each of the unit pixels for resetting the photoelectric conversion element every time a pixel signal is outputted from the relevant unit pixel.
According to a second aspect of the present invention, there is provided a method of driving a solid-state image sensor of the above structure. The method comprises the steps of resetting the photoelectric conversion element every time a pixel signal is outputted from the relevant unit pixel; then delivering a pre-reset signal and a post-reset signal from each unit pixel and taking the difference between the pre-reset signal and the post-reset signal.
And according to a third aspect of the present invention, there is provided a camera which comprises an optical system for focusing incident light from an object scene to form an image thereof; a solid-state image sensor comprising unit pixels each having a photoelectric conversion element for converting the optical image formed by the optical system into electric signal charge and then storing the signal charge obtained through such photoelectric conversion, an amplifying element for converting into an electric signal the signal charge stored in the photoelectric conversion element, and a select switch for selectively outputting the pixel signal
Shiono Koichi
Suzuki Ryoji
Ueno Takahisa
Yonemoto Kazuya
Garber Wendy R.
Rosendale Matthew L
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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