Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1998-09-21
2001-02-06
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140AG
Reexamination Certificate
active
06184513
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image sensor chip for reading an image of a scanned object, and an image sensor comprising a plurality of the image sensor chips.
BACKGROUND ART
According to a prior art image sensor chip, image signals from a plurality of photoelectric elements are serially output from an output pad without being amplified. A prior art image sensor comprising a plurality of such image sensor chips has an amplifying circuit formed on an amplifying circuit board separate from an image sensor chip board. The image signals from each of the image sensor chips are supplied to the amplifying circuit via a wiring pattern and a connector of the image sensor chip, and a wiring pattern of the amplifying circuit. After the signals are amplified by the amplifying circuit, the signals are serially output via the wiring pattern of the amplifying circuit, a connector and other components to an external circuit.
However, according to the prior art, the image signals from each of the image sensor chips are supplied to the amplifying circuit only after passing through the wiring pattern and the connector of the image sensor chip, and the wiring pattern of the amplifying circuit. Therefore, the signals are subject to noise, and it was difficult to obtain accurate image signals of an original image. Specifically, the image signals have a small voltage whereas the amplifying circuit has a large input impedance. As a result, noise can enter easily, and may become very large if there is a long path between the image sensor chip and the amplifying circuit. Especially, if there is such an apparatus as a laser printer located near by, the image signals can be badly affected by the noise from the laser printer.
This problem may be solved for example, by encasing the image sensor in a structure made of metal such as aluminum. However, this method of electromagnetically shielding the internal circuitry of the image sensor increases manufacturing cost of the image sensor.
Another option for solution may be providing each of the image sensor chips with a built-in amplifying circuit so that each image sensor chip can output amplified image signals.
With such an arrangement, however, the amplifying circuit built in each of the image sensors will have different offset from each other, making difficult to obtain accurate image signals of an original image. This problem is particularly serious in image sensing of a colored or gradated image because the difference in offsets can easily result in difference in the gradation or color.
This problem may be solved by adding a correction circuit for correcting the differences in the offsets. The correction circuit may be added to an image signal processing circuit which processes the image signals after the signals are output from the image sensor. However, this arrangement increases manufacturing cost of the apparatus which includes the image sensor.
Another option for solution may be providing one of the image sensor chips of each row with a built-in amplifying circuit so that image signals from all of the image sensor chips of that row can be amplified by this amplifying circuit before output to an external circuit.
This arrangement can solve the problem of the difference in offset within each row. In addition, there will be less problem of noise than in the case where the amplifying circuit is made separately on the amplifying circuit board. With this arrangement, however, two types of image sensors must be manufactured for mounting on an image sensor chip board. This decreases advantages of mass production in manufacture of the image sensor chips. Further, a more complex procedure must be used for mounting the image sensor chips on the image sensor chip board, increasing manufacturing cost of the image sensor.
As exemplified above, each of the three methods has advantages and disadvantages. Preferably therefore, any of the three methods should be selectively usable depending upon application of the image sensor. However, manufacturing different types of image sensors for each method will further decrease the advantages of mass production in the manufacture of image sensor chips, increasing further the manufacturing cost of the image sensor.
DISCLOSURE OF THE INVENTION
It is therefore an object of the present invention to provide an image sensor which can selectively take an output mode of, outputting image signals without amplification, outputting image signals amplified by an amplifying circuit built for each of the image sensor, or outputting image signals amplified by an amplifying circuit provided in each row of the image sensor chips, by means of wirebonding at the time of manufacture.
Another object of the present invention is to provide an image sensor chip for such an image sensor.
According to a first aspect of the present invention, there is provided an image sensor chip comprising a plurality of photoelectric elements for converting light reflected by a scanned object into analog image signals, a selecting circuit for sequential takeout of the serial image signals from respective output terminals of the photoelectric elements, a first pad for output of the image signals taken out serially by the selecting circuit, an amplifying circuit capable of amplifying the image signals from the plurality of photoelectric elements, a second pad connected to an input terminal of the amplifying circuit, and a third pad connected to an output terminal of the amplifying circuit.
With the above arrangement, image signals before amplification can be obtained by taking image signals from the first pad. Image signals after amplification can be obtained by entering image signals from the first pad into the second pad, and then taking the image signals from the third pad. Further, other image sensor chips having the same construction may have image signals from their respective first pads entered commonly into the second pad. Then, by taking image signals from the third pad, amplified image signals from the plurality of image sensor chips can be obtained. Thus, by using a plurality of this image sensor chip, it becomes possible without increasing the manufacturing cost, to provide the image sensor which can selectively take an output mode of, outputting image signals without amplification, outputting amplified image signals, or outputting image signals amplified by another image sensor chip, by means of wirebonding at the time of manufacture.
The object to be scanned may be an image on a piece of paper or a film of resin, or the image may not necessarily be on a sheet material.
The photoelectric element may be but not limited to a photodiode or a phototransistor.
The selecting circuit may be but not limited to a shift register or a CCD.
The amplifying circuit may be but not limited to an operational amplifier.
An image sensor chip according to the preferred mode of embodiment further comprises a first switching circuit operated by external control signals for switching between a state in which the image signals from the selecting circuit are supplied to the first pad and another state in which the image signals are not supplied to the first pad, and a second switching circuit operated by external control signals for switching between a state in which output signals from the amplifying circuit are supplied to the third pad and another state in which the output signals from the amplifying circuit are not supplied to the third pad.
With the above arrangement, the first or the second switch circuit may be opened when the respective first or third pad is not used for obtaining the image signals or the amplified image signals. Thus, the transfer path of the image signals can be effectively protected from noise entering into the circuit or being output from the first or third pad. This makes possible to maintain a good reading performance, and is especially advantageous in eliminating a noise from entering the amplifying circuit and then being output from the third pad as a big noise.
Each of the first and second switching circuits may be made by
Lee John R.
Merchant & Gould P.C.
Rohm & Co., Ltd.
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