Solid-state image sensing device with image pick-up...

Details Solid-state image sensing device with image pick-up... Solid-state image sensing device with image pick-up...

1998-12-03

2001-02-13

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

C250S332000, C250S257000

Reexamination Certificate

active

06188069

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a solid-state image sensing device and, more particularly, to a solid-state infrared image sensing device having a pixel array implemented by bolometers and a read-out circuit for producing a noise-free image carrying signal.
DESCRIPTION OF THE RELATED ART
A typical example of the solid-state infrared image sensing device is disclosed in Japanese Patent Publication of Unexamined Application No. 8-105794. Bolometers are incorporated in the prior art solid-state infrared image sensing device, and convert an infrared image to an electric image carrying signal. However, the prior art solid-state infrared image sensing device suffers from a fixed pattern noise due to dispersion of resistance between the bolometers.
FIG. 1
illustrates the prior art solid-state infrared image sensing device. The prior art solid-state infrared image sensing device comprises a pixel array
1
, a vertical shift register
2
, a selector
3
and a horizontal shift register
4
. Plural image pick-up pixels PX00, PX01, PX0m, PX0n, PX10, PX11, PX1m, PX1n, PXj0, PXj1, PXjm, PXjn, PXk0, PXk1, PXkm and PXkn are arranged in rows and columns, and form the pixel array
1
. The image pick-up pixels PX00 to PXkn are similar in arrangement to one another, and each of the image pick-up pixels PX00 to PXkn is implemented by a series combination of an n-channel enhancement type field effect transistor T
1
and a bolometer BM
1
. The bolometer BM
1
is formed of titanium, and varies the resistance together with the temperature thereon. The n-channel enhancement type field effect transistors T
1
are grounded through source lines
5
. The bolometer BM
1
is sensitive to electromagnetic power such as infrared, and varies the resistivity depending upon the magnitude of the incident power.
The columns of image pick-up pixels PX00-PXk0, PX01-PXk1, . . . PX0m-PXkm and PX0n-PXkn are associated with vertical signal lines V
0
, V
1
, . . . , Vm and Vn, respectively, and each of the vertical signal lines V
0
to Vn is connected between the bolometers BM
1
of the associated column and the selector
3
. The rows of image pick-up pixels PX00-PX0n, PX10-PX1n, PXj0-PXjn and PXk0-PXkn are respectively associated with row selecting lines H
0
, H
1
, . . . Hj and Hk, and each of the row selecting lines H
0
to Hk is connected to the gate electrodes of the n-channel enhancement type field effect transistors T
1
of the associated row of image pick-up pixels.
The row selecting lines H
0
to Hk are connected to the vertical shift register
2
, and the vertical shift register
2
sequentially changes the row selecting lines H
0
to Hk to active high level, and the bolometers BM
1
of each row of image pick-up pixels are concurrently connected through the source lines
5
to the ground.
The selector
3
includes plural transfer gates TG
1
connected between the vertical signal lines V
0
to Vn and a horizontal signal line
5
a
and inverters INV
1
respectively provided for the transfer gates TG
1
. Each of the transfer gates TG
1
is implemented by a parallel combination of an n-channel enhancement type field effect transistor and a p-channel enhancement type field effect transistor. The horizontal signal line
5
a
is connected to an output node
6
. The horizontal shift register
4
has plural control lines CL
0
/CL
1
/CLm and CLn, and sequentially changes the control lines CL
0
to CLn to the active level. The control lines CL
1
to CLn are respectively associated with the transfer gates TG
1
. Each control line is directly connected to the gate electrode of the n-channel enhancement type field effect transistor of the associated transfer gate TG
1
, and is connected through the inverter INV
1
to the gate electrode of the p-channel enhancement type field effect transistor of the associated transfer gate TG
1
. The horizontal shift register
4
sequentially changes the control lines CL
0
to CLn to the active level. Thus, the vertical shift register
2
and the horizontal shift register
4
sequentially connect the image pick-up pixels PX00 to PXkn to the output node
6
.
When an infrared image falls on the pixel array
1
, the bolometers BM
1
differently vary the resistance depending upon the intensity dispersion of the infrared image. An external circuit (not shown) applies a predetermined potential level to the output node
6
, and the vertical shift register
2
, the horizontal shift register
4
and the selector
3
sequentially connect the image pick-up pixels PX00 to PXkn to the output node
6
. The potential difference across each bolometer BM
1
is read out from the output node
6
to the external circuit as an image carrying signal. The variation of the potential difference is representative of the infrared image.
A problem is encountered in the prior art solid-state image sensing device in that complicated correction circuit is required for eliminating fixed pattern noise. The fixed pattern noise is due to dispersion of resistance among the bolometers BM
1
. In detail, the bolometers BM
1
are fabricated on a diaphragm through an etching process, and two dimensional dispersion takes place in the array of bolometers BM
1
due to the microloading effect in the etching process.
FIGS. 2A and 2B
show the dispersion of resistivity. When the pixel array
1
has corners CR
1
, CR
2
, CR
3
and CR
4
as shown in
FIG. 2C
, the resistivity inclines in the direction of rows of image pick-up pixels as indicated by plots PL
1
without any infrared image, and the resistivity inclines in the direction of columns of image pick-up pixels as indicated by plots PL
2
without any infrared image. As a result, the resistivity is two dimensionally dispersed as indicated by plots PL
3
over the pixel array
1
. The dispersion is causative of the fixed pattern noise. The fixed pattern noise rides on the output image carrying signal, and is supplied to the external circuit together with the signal components representative of the infrared image.
The fixed pattern noise does not allow the output image carrying signal to represent the infrared image, and is serious in the circuit D-range. For this reason, correction is required for the output image carrying signal. A correction circuit is incorporated in the external circuit, and includes an integration circuit, an analog-to-digital converter, a memory, a digital-to-analog converter and a microprocessor. The dispersion of resistance is represented by digital values, and the digital values are stored in the memory.
The image carrying signal is supplied to the integration circuit, and the output signal of the integration circuit is periodically sampled. The sampled values are converted to a series of digital data signals, and the digital data signals are temporarily stored in the memory. The digital values are subtracted from the values of the sampled values, respectively. As a result, the fixed pattern noise is eliminated from the image carrying signal. After the subtraction, the digital signals are supplied to the digital-to-analog converter, and are formed into an image carrying signal without the fixed pattern noise. Thus, the prior art correction circuit eliminates the fixed pattern noise inherent in the bolometer array from the output image carrying signal. However, the prior art correction circuit is so complicated that the external circuit occupies wide area. Moreover, another kind of noise is introduced during the elimination of the fixed pattern noise.
SUMMARY OF THE INVENTION
It is therefore an important object of the present invention to provide a solid-state image sensing device, which makes a read-out circuit simple without undesirable influence of the fixed pattern noise.
It is also an important object of the present invention to provide a simple read-out circuit available for the solid-state image sensing device.
In accordance with one aspect of the present invention, there is provided a solid-state image sensing device comprising a plurality of image pick-up pixels respectively including bolometers varying the resistivity thereof dependi

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