Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1999-04-14
2002-04-02
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
C250S208100, C257S231000, C257S291000, C348S300000, C348S297000
Reexamination Certificate
active
06366321
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to solid-state imaging device and, more particularly, is directed to a solid-state imager having FETs (field effect transistors) and load capacitors.
As the demand for high resolution solid-state imaging devices increases, there have been developed so far internal amplifier type solid-state imaging devices for amplifying light signal charges at every pixel. As the internal amplifier type solid-state imaging device, there are mainly various kinds of imaging device structures, such as a static induction transistor (SIT), an amplifying type MOS imager (AMI), a charge modulation device (CMD) and a BASIS (base-stored image sensor) using a bipolar transistor as a pixel.
An amplifier type solid-state imaging device called a WAM (well control amplified MOS (metal oxide semiconductor) imager) is known as one of such internal amplifier type solid-state imaging devices. In this amplifier type solid-state imaging device, holes (signal charges) obtained by photoelectric conversion are accumulated in a P-type potential well of an N-channel MOS transistor (pixel MOS transistor) and the change of a channel current based on the change of potential in the P-type potential well (i.e., change of potential in the back gate) is output as a pixel signal.
FIG. 1
of the accompanying drawings shows an example of an amplifier type solid-state imaging device
11
. As shown in
FIG. 1
, there are arrayed pixel MOS transistors [unit pixels (cells)]
1
in a matrix fashion. The gate of each pixel MOS transistor
1
is connected to a vertical scanning line
3
scanned by a vertical scanning circuit
2
formed of a shift register or the like. The drain of each pixel MOS transistor
1
is connected to a power supply line (line to which a voltage V
DD
is supplied)
4
and the source thereof is connected to a vertical signal line
5
.
Each of the signal vertical signal lines
5
is connected with a load MOS transistor
6
whose gate has a bias voltage V
B
applied thereto. A sample and hold circuit
7
for sampling and holding a pixel signal also is connected to each vertical signal line
5
. In
FIG. 1
, reference numeral
8
depicts a horizontal scanning circuit. The horizontal scanning circuit
8
outputs a pixel signal from the sample and hold circuit
7
through a horizontal output signal line
10
by sequentially supplying a scanning signal to the gate of each of horizontal MOS switches
9
.
In the amplifier type solid-state imaging device
11
, as shown in the schematic diagram of
FIG. 1 and a
diagram of an equivalent circuit of
FIG. 2
realized when a pixel is scanned, the unit pixel, i.e. the pixel MOS transistor
1
, is scanned by the vertical scanning circuit
2
through the vertical scanning line
3
. Then, a signal obtained from a source-follower circuit formed of the pixel MOS transistor
1
and the load MOS transistor
6
connected to the vertical signal line
5
as a constant current source is sampled and held by the sample and hold circuit
7
and the horizontal MOS switches
9
connected to the horizontal scanning circuit
8
are sequentially energized to thereby output the signal of each pixel MOS transistor
1
through the horizontal
2
output signal line
10
.
Specifically, the scanned pixel MOS transistor
1
and the load MOS transistor
6
operate as the source-follower circuit to output a source potential obtained under the condition that a current is constantly flowed in the pixel MOS transistor
1
via the sample and hold circuit
7
and the horizontal MOS switch
9
. Therefore, it is possible to obtain a signal output of the solid-state imaging device by carrying out the above-mentioned operation at every horizontal scanning line while the vertical scanning line
3
for scanning the pixel MOS transistor
1
is being changed.
However, in the above-mentioned case, operation conditions of the pixel MOS transistor
1
disposed away from the load MOS transistor
6
and the pixel MOS transistor
1
disposed near the load MOS transistor
6
are changed by a distributed resistance with the result that sensitivity is deteriorated in the vertical direction.
If a constant current property of the load MOS transistor
6
operated as the constant current source is unsatisfactory, there is then the disadvantage that sensitivity of the solid-state imaging device is lowered. In other words, the load MOS transistor
6
operated as the constant current source is not an ideal constant current source. Therefore, if the source current of the pixel MOS transistor
1
is changed, then the constant current is fluctuated very slightly and a fluctuated amount of the constant current causes sensitivity to be lowered.
Moreover, since the constant current is always flowed when a signal voltage is read out from the pixel MOS transistor
1
, an imaging device consumes much power.
Further, when the constant current of the load MOS transistor
6
is fluctuated, there is generated a vertical stripe-shaped fixed pattern noise (FPN) which is difficult to be removed by signal processing.
Furthermore, when a signal voltage is read out from the pixel MOS transistor
1
, the constant current, i.e. a relatively large drain current is flowed, so that a mutual conductance gm of the pixel MOS transistor
1
is large. As a result, a random noise generated from the pixel MOS transistor
1
becomes large as compared with the mutual conductance gm.
OBJECTS AND SUMMARY OF THE INVENTION
In view of the aforesaid aspect, it is an object of the present invention to provide an amplifier type solid-state imaging device of a capacitor load operation system in which sensitivity can be made uniform, sensitivity can be increased, a power consumption can be reduced and a fixed pattern noise can be removed.
It is another object of the present invention to provide an amplifier type solid-state imaging device of a capacitor load operation system which can be made more reliable and in which an arrangement of a horizontal output circuit portion can be simplified.
It is a further object of the present invention to provide a solid-state imaging device of a capacitor load operation system in which a random noise of a pixel transistor can be reduced.
According to a first aspect of the present invention, there is provided a solid-state imaging device which is comprised of a plurality of pixel MOS transistors for storing signal charges generated by photoelectric conversion, each of the pixel MOS transistors composed of a gate electrode connected to a vertical scanning line, a drain connected to a voltage source and a source connected to a vertical signal line, a capacitor connected between the vertical signal line and a fixed potential, a reset device for resetting a potential of the capacitor to set a reset potential, and a switch for controlling a connection between one of the pixel MOS transistors and the capacitor so that a potential of the capacitor has the same potential as a channel potential of the pixel MOS transistor selected.
According to a second aspect of the present invention, there is provided a solid-state imaging device which is comprised of a plurality of pixel bipolar transistors for storing signal charges generated by photoelectric conversion, each of the bipolar pixel transistors being composed of a base connected to a scanning line, a collector connected to a voltage source and an emitter connected to a vertical signal line, a capacitor connected between the vertical signal line and a fixed potential, a switch disposed between the vertical signal line and the capacitor and a reset device for resetting the respective potentials of the capacitor and the vertical signal line.
In accordance with a third aspect of the present invention, there is provided a solid-state imaging device which is comprised of a plurality of pixel bipolar transistors for storing signal charges generated by photoelectric conversion, each of the pixel bipolar transistors being composed of a base connected to a vertical scanning line, a collector connected to a voltage source and an emitter
Garber Wendy R.
Sonnenschein Nath & Rosenthal
Sony Corporation
Vu Ngoc-Yen
LandOfFree
Solid state imaging device having a reset switch for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Solid state imaging device having a reset switch for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solid state imaging device having a reset switch for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2918229