Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1998-02-02
2002-10-22
Ho, Tuan (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
C348S241000, C348S301000
Reexamination Certificate
active
06469740
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to physical quantity distribution sensors and it further relates to physical quantity distribution sensor driving methods.
Recently, there have been increasing demands for physical quantity distribution sensors used for the detection of the one-/two-dimensional distribution of various physical quantities. In the field of solid-state imaging technology for detecting a light intensity as a physical quantity, a so-called amplification type solid-state imaging device has attracted attention. A typical amplification type solid-state imaging device has a plurality of picture elements each comprising a photoelectric conversion section operable to generate a signal charge by photoelectric conversion of light incident thereon, a storage region for storing the signal charge, and a driving element such as a field-effect transistor (FET) for providing a signal according to the signal charge. The storage region is connected to a gating control region of the driving element such as a FET gate region and bipolar transistor base region, to achieve control of the output value of the driving element by the electrical potential of the storage region that varies according to signal charge amounts stored therein. Some amplification type solid-state imaging devices employ a storage region that serves also as a transistor gating control region.
Although such an imaging device has amplifying transistors functioning as driving elements allocated to each pixel, these amplifying transistors differ in transistor characteristic from one another. If the characteristic of a transistor in the absence of signal charge, for instance, the threshold voltage, Vt, of a FET, varies, this results in variations in the output value of the transistor even when each photoelectric conversion section is illuminated by the same amount of incident light thereby equalizing the electrical potentials of the gating control regions. As a result, spatially fixed noise, known as fixed pattern noise (FPN), occurs, therefore causing severe damage to the qualities of image.
Japanese Patent Application Laying Open Gazette No. 5-252445 shows an amplification type solid- state imaging device with a view to preventing the occurrence of FPN. This prior art imaging device is described with reference to FIG.
8
. An amplifying transistor M
1
for amplifying a sensor potential, V
S
, is disposed for each pixel. A feedback circuit
3
including a differential amplifier
2
is provided which supervises the channel electrical potential of the transistor M
1
and fixes same at a reference electrical potential, V
R
′, at reset operation time. A reset is carried out by adjustment of V
S
using the output of the amplifier
2
at the time when a reset transistor M
3
is electrically conductive. The
FIG. 8
imaging device circuitally achieves a reduction of the variation in Vt of the transistor M
1
.
In such a prior art imaging device, at the time of supervising the channel electrical potential of the transistor M
1
of each pixel, a switching transistor M
2
is placed in an electrically non-conductive (off) state and an electrical potential at a node between the transistors M
1
and M
2
is applied to an input section of the amplifier
2
. The reason for this may be that the imaging device employs a structure in which the magnitude of a current flowing in the transistor M
1
is read as an output, I
S
, and it is impossible to detect the channel electrical potential of the transistor M
1
at the time when the transistor M
2
is electrically conductive. It is required that the electrical potential at the node between the transistors M
1
and M
2
, V
0
, be applied to the amplifier
2
. This requires extra interconnection lines for providing connections between each pixel and the amplifier
2
. In order to perform feedback on every pixel by the single amplifier
2
, it is necessary to newly provide transistors to each pixel in addition to the switching transistors used for pixel selection. Accordingly, it is impractical for area sensors, in which a great number of pixels are 2-D arranged, to adopt the above-described structure.
Feedback operations by the amplifier
2
are performed, not at the time when signal charge stored in a photo sensor
1
is read through the transistors M
1
and M
2
, but at the time when the transistor M
2
is in the non-conductive state. In accordance with the prior art technique, feedback is not carried out based on the output in the same state as that of the actual output operation time, which results in insufficient improvements on the accuracy of feedback.
Accordingly, an object of the present invention is to provide physical quantity distribution sensors and its driving methods for getting rid of noise due to variations in the characteristics of driving elements by high-accuracy feedback.
SUMMARY OF THE INVENTION
The present invention provides a physical quantity distribution sensor comprising a plurality of unit cells, each such unit cell including: an information storage region responsive to a physical stimulus and capable of a transition from a first electrical potential state to a second electrical potential state according to the physical stimulus; a driving element for providing at an output portion thereof an electrical potential according to the electrical potential state of the information storage region; and a switching element connected to the output portion of the driving element; the physical quantity distribution sensor further comprising: an output section for receiving, when the switching element is electrically conductive, an output from the driving element which is connected to the switching element and outputting a signal according to the electric potential state of the information storage region; an output adjustment section for receiving, when the switching element is electrically conductive, the output from the driving element and adjusting the first electrical potential state of the information storage region in order that the output from the driving element may substantially equal a reference electrical potential; and a unit cell selector for controlling an electrically conductive
on-conductive state of the switching element.
In a preferred embodiment, the driving element is a MOS transistor having: a gate connected to the information storage region; a source for functioning as the output portion and connected to the output section; and a drain for receiving a supply voltage.
In a preferred embodiment, the physical quantity distribution sensor further comprises a load element connected to the source of the driving element wherein the driving element and the load element together form a source follower circuit.
In a preferred embodiment, the switching element is a MOS transistor having: a gate for receiving a signal from the unit cell selector; a drain connected to the source of the driving element; and a source connected to the output section.
In a preferred embodiment, the information storage region has: a sensing section for converting the physical stimulus into an electric charge; and a storage section for storing the electric charge.
In a preferred embodiment, the sensing section is a p-n junction type photoelectric conversion element.
In a preferred embodiment, the storage section is a p-n junction type capacitor element.
In a preferred embodiment, each of the plurality of unit cells further includes a reset element operable to perform a forcible reset of the electrical potential state of the information storage region to the first electrical potential state in response to a reset pulse.
In a preferred embodiment, the reset element is a MOS transistor that receives at a gate region thereof the reset pulse.
In a preferred embodiment, the reset element is a MOS transistor that receives at a gate region thereof the output of the output adjustment section.
In a preferred embodiment, the output of the output adjustment section is supplied, through the reset element, to the information storage region at the time when the reset element perfo
Kuroda Takao
Masuyama Masayuki
Ho Tuan
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
Ye Lin
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