Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1999-02-08
2003-09-09
Christensen, Andrew (Department: 2615)
Television
Camera, system and detail
Solid-state image sensor
C348S316000, C348S265000, C257S215000, C377S062000, C377S063000
Reexamination Certificate
active
06618088
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a charge transfer device, and more particularly to a charge transfer device including one-dimensional charge transfer elements for converting a color image into an electric signal.
2. Description of the Relates Art
A conventional charge transfer device which employs a one-dimensional charge transfer element having a plurality of pixels arranged in a row is described below. In order for the conventional charge transfer device to read a two-dimensional color image, reflection light from or transmission light through an original upon which white light is impinged is separated into three colors of red, blue and green, and the lights of the colors are converted into electric signals by the charge transfer elements and the electric signals are stored temporarily into a memory. As the one-dimensional charge transfer elements, or the original, are being moved, the reflection light or transmission light is then successively converted into electric signals, and the respective electric signals of red, blue and green obtained from the same places are composed by a computer to regenerate a two-dimensional color image. This method requires one one-dimensional charge transfer element for each of the three colors of red, blue and green. Further, the electric signals obtained by conversion of the lights of the three colors obtained from the same place must be composed into one signal. Therefore, as the distance (hereinafter referred to as line distance) between a pixel row of a certain one-dimensional charge transfer element and a pixel row of another one-dimensional charge transfer element increases, an increasing memory capacity is required to store color information. For example, if the line distance increases doubles, the necessary memory capacity also increases doubles. The increase in the memory capacity in turn may make of an image reading apparatus which employs the charge transfer device costly. Furthermore, if the original is fed slantwise, the larger the line distance becomes, the more resolution will deteriorate.
The line distance is thus important factor influencing picture quality and cost. Assuming that the length of a pixel in a longitudinal direction is equal to 1, the line distance is essentially an integer and will not be a decimal.
FIG. 1
is a plan view of a conventional charge transfer device which includes three one-dimensional charge transfer elements for reading a color image.
As shown in
FIG. 1
, the conventional charge transfer device includes one-dimensional charge transfer elements of first to third rows corresponding to the three primary colors of light, that is, red, blue and green respectively. It is to be noted that, the arrangements of the colors are different from product to product, and one-dimensional charge transfer elements of three rows are required to read a color original.
Each of the one-dimensional charge transfer elements includes a plurality of pixel elements
1
for converting optical signals into charges, an element separation area
2
, CCDs (Charge Coupled Devices)
4
, and a readout electrode
3
for controlling reading out of charges from pixel elements
1
into CCDs
4
. Each of the CCDs
4
has transfer electrodes
19
1
,
19
2
,
11
1
,
11
2
in this order. Readout electrode
3
is made of polysilicon in the same step as that for transfer electrodes
11
1
,
11
2
.
FIG. 2
shows a section of
FIG. 1
taken along line G-G′, i.e., a structure of a portion through which charge is read out from pixel element
1
to CCD
4
and a potential distribution during operation.
FIG. 3
shows a section of
FIG. 1
taken along line H-H′, i.e., a cross section of CCD
4
, and a potential distribution during operation.
In the conventional charge transfer device, each of the CCDs
4
has a two-phase driving structure. A CCD
4
consists of a N-type semiconductor substrate
5
, P-type well
6
, a photodiode N-type well
7
which forms pixel element
1
, photodiode P-type region
8
which forms pixel element
1
, transfer electrodes
19
1
,
19
2
,
11
1
and
11
2
, N-type well
10
, N-type diffusion layer region
12
, and oxide film
13
formed by implanting ions of boron or the like in self alignment into transfer electrodes
19
1
,
19
2
.
Next, operation of the conventional charge transfer device will be described with reference to
FIGS. 1
to
3
.
Charges are generated in pixel elements
1
of
FIG. 1
dependent on incident light amounts and a storage time, and are read out to CCDs
4
through the application of a voltage of 5 V to readout electrode
3
. Signal charges
15
are read out into CCDs
4
under the control of readout electrode
3
. The charges read out into CCDs
4
are transferred in one direction through the successive application of a voltage to transfer electrodes
19
1
,
19
2
and transfer electrodes
11
1
,
11
2
of CCDs
4
, as shown in FIG.
3
. The transferred charges are then converted into voltages by charge detectors (not shown) provided at the terminals of CCDs
4
to be successively read out. The charges generated in pixel elements
1
at the first to third rows are successively transferred by CCDs
4
disposed for the individual rows to be converted into voltages.
The conventional charge transfer device shown in
FIG. 1
, in order to read in a color image, an arrangement employs, wherein three one-dimensional charge transfer elements of the same structure are juxtaposed in three rows. With this arrangement, the line distance cannot be made equal to or smaller than double the length of pixel elements
1
in the longitudinal direction.
Another conventional example is shown in
FIG. 4
wherein the line distance can be made equal to or smaller than double the length of pixel elements
1
in the longitudinal direction.
As shown in
FIG. 4
, in this charge transfer device, the one-dimensional charge transfer element of the first row is inverted in an upward and downward direction in the figures, to reduce the line distance between the first and second rows. This approach has a drawback in that, since the line distance between the first and second rows and the line distance between the second and third rows are not equal to each other, if an original is fed slantwise as mentioned above, the ratio in color displacement differs from color to color, resulting dirty image.
Yet another conventional example which intend to solve the aforementioned problem is shown in FIG.
5
.
In the conventional charge transfer device shown, pixel elements
1
of the first, second and third rows are arranged side by side and all of the line distances between adjacent pixel elements
1
is made equal to the length of pixel elements
1
in the longitudinal direction. Charges generated in pixel elements
1
in the one-dimensional charge transfer element of the second row are read out into CCDs
4
through pixel elements
1
of the third row.
FIG. 6
shows a sectional view of
FIG. 5
taken along line I-I′ and a potential distribution. A readout electrode
3
is interposed between pixel elements
1
of the second and third rows to read out charges generated in pixel elements
1
of the second row into CCDs
4
through pixel elements
1
of the third row.
In this conventional charge transfer device, the line distance is equal to the length of pixel elements
1
in the longitudinal direction. Consequently, the required memory capacity is at the least and, even if an original is fed slantwise, a resulting image would not be dirty. However, if light to be incident on pixel elements
1
of the third row is not intercepted, when reading out charges from the one-dimensional charge transfer element of the second row, then a mixture of colors will occur in pixel elements
1
of the third row.
In short, the conventional charge transfer device is disadvantageous in that, since charges of the one-dimensional charge transfer element of the second row must be passed through the one-dimensional charge transfer element of the third row, a color mixture will occur, which re
Miwada Kazuo
Tsunai Shiro
Christensen Andrew
NEC Electronics Corporation
Tran Nhan
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