Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-04-26
2001-09-18
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140AG
Reexamination Certificate
active
06291810
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an one-dimensional image sensor for converting the reflected light from a manuscript which is irradiated with light into an electrical signal and can be applied to an image reading apparatus such as a FAX.
FIG. 10
is a circuit diagram showing a configuration of a contact type one-dimensional image sensor IC which is used in a conventional image reading apparatus for use in a FAX. As shown in
FIG. 10
, the conventional image reading apparatus is such that the output signals outputted from phototransistors P
1
to Pn are read out to a common signal line
1
by turning on successively switches S
1
to Sn. In this connection, reference symbol AMP designates an amplifier for amplifying the output signals which are outputted from the phototransistors P
1
to Pn.
The contact type phototransistor one-dimensional image sensor as described above is disclosed in Japanese unexamined patent application publication S61-124171(1986).
SUMMARY OF THE INVENTION
However, in such a one-dimensional image sensor, there arises a problem in that since the carriers remaining in the base of the phototransistor are removed through the emitter of the phototransistor, the base electric potential can not be sufficiently reset to the initial state and hence the residual image is remarkable.
In the light of the foregoing, the present invention was made in order to solve the above-mentioned problem associated with the prior art, and it is therefore an object of the present invention to provide an image sensor which is inexpensive, has smaller residual image and is capable of obtaining the effective bright output with accuracy.
In order to solve the above-mentioned problem, the image sensor according to the present invention is designed as follows.
According to the present invention, there is provided an image sensor which is constructed by arranging and mounting linearly a plurality of linear image sensor ICs, wherein a unit light receiving circuit includes: a photodiode acting as a light receiving element; an amplifier for amplifying a signal outputted from the photodiode; and a reading switch for reading out an output signal of the amplifier, and the image sensor IC is constructed in such a way that output signals, each varying depending on the amount of received light, from the plurality of unit light receiving circuits are read out successively in the order of the arrangement of the unit light receiving circuits to a signal output terminal therethrough.
In addition, in the above-mentioned image sensor IC, a first electrode of a reset switch is connected to a common signal line, an electric potential at a second electrode of the reset switch is fixed to an electric potential giving an initial electric potential by which the state of the photodiode is reset to the initial state, and the reset switch is temporarily closed when an image signal is outputted therethrough and is opened or closed in such a way that the electric potential of the common signal line is rapidly brought close to the initial electric potential.
In addition, preferably, a reference voltage circuit may be configured in terms of a configuration of the amplifier circuit in such a way that the difference between the electric potential inputted to the amplifier and the electric potential outputted from the amplifier is equal to the difference between the electric potential by which the state of the photodiode is made the initial state and the initial electric potential by which the common signal line is reset due to the back gate effect of a MOS transistor.
In addition, a first electrode of another reset switch is connected to an output terminal, an electric potential at a second electrode of the another reset switch is fixed to the electric potential giving an initial electric potential by which the state of another amplifier is reset to the initial state, and the another reset switch is temporarily closed when outputting therethrough an image signal and is opened or closed in such a way that the electric potential at the signal output terminal is rapidly brought close to the initial electric potential. As a result, against even the increase of the external load capacity which occurs when connecting a plurality of linear image sensor ICs linearly, the electric potential at the signal output terminal can be rapidly brought close to the initial electric potential.
In addition, if the amplifiers start, after having been sufficiently stabilized, their amplifying operations a fixed time period before an image signal of the light receiving element which is arranged in the first stage of the image sensor starts to be outputted, and complete their amplifying operations after the operation of outputting an image signal of the light receiving element which is arranged in the final stage thereof has been completed and the state of that light receiving element is returned back to the initial state, since those amplifiers are operated stably and selectively, those amplifiers serve so as to provide the less current consumption.
An output signal is read out to a dummy signal output terminal through a dummy photodiode, an amplifier for amplifying a signal outputted from the dummy photodiode and a reading switch for reading out therethrough the output signal. An electric potential at an electrode of a reset switch is fixed to the electric potential giving the initial electric potential by which the state of the dummy photodiode is reset to the initial state at all times. The reset switch is temporarily closed when an image signal is outputted and is opened or closed in such a way that the electric potential of the common signal line is rapidly brought close to the initial electric potential. In addition, a first electrode of another reset switch is connected to a dummy signal output terminal, and an electric potential at a second electrode of the reset switch is fixed to the electric potential giving the initial electric potential by which the reset is always made to the initial state. These circuit configurations and the circuit constants are respectively made identical to those of the circuit for outputting an image signal from the photodiode acting as the light receiving element, and the same signal as the output signal in the dark state is outputted.
An image sensor according to the present invention is designed in such a way that a photodiode is used as a light receiving element of a unit block and an amplifier is connected to the photodiode within the block so that the terminal voltage of the photodiode varying depending on the amount of received light is outputted successively in the form of an image signal through the amplifier, and also a dummy photodiode is provided which has the same configuration as that of the unit block of the light receiving element and the state of which is reset to the initial state at all times and which outputs a dummy signal equal to an output signal in the dark state of the photodiode as the light receiving element, thereby enabling the difference between the image signal output and the dummy output signal to be obtained.
REFERENCES:
patent: 4564864 (1986-01-01), Maeshima
patent: 5315102 (1994-05-01), Abe et al.
patent: 5557121 (1996-09-01), Kozuka et al.
patent: 6002287 (1999-12-01), Ueno et al.
Kawahara Yukito
Machida Satoshi
Yokomichi Masahiro
Adams & Wilks
Lee John R.
Seiko Instruments Inc.
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