JPH03139957A - Image reader - Google Patents

Abstract

PURPOSE:To suppress a change in an image output due to a change in temperature by providing the image reader with an image sensor having the 1st photoelectric conversion element for reading out the reflected light of an original and the 2nd photoelectric conversion element interrupted from light and a signal correcting means for correcting an image signal outputted from the 1st element by an output signal from the 2nd element. CONSTITUTION:A shift register 101 for shifting charge proportional to the quantity of light emitted from respective photoelectric conversion elements successively to the post stage, a photodiode 102 being a photoelectric conversion element for converting an image signal into an electric signal, a photoelectric conversion element 103 having a similar function to an element with its photodetecting part of the photoelectric conversion element light-shieled, image output signal buffer amplifiers 104, 105. and a differential amplifier 106 for subtracting a dark part image output signal from an image output signal are integrated. When one of two image reading element is light-shieled, the image output signal of the other element can be corrected. Thereby, a change in an image output due to the partial or overall temperature change of the image sensor can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reading device that reads an image using an image sensor.

(Conventional technology) Conventionally, image sensors used for image reading are:
In order to suppress changes in the n1 time output signal due to temperature changes, there is a system that performs temperature control using the Bertier effect or the like.

Here, as a method to cope with the output signal change due to the E-temperature of the entire image sensor due to the lighting of a halogen lamp etc. for original In lighting, there are two methods: one to control the temperature change of the entire image sensor, and one to control the temperature change of the entire image sensor. Two methods are known for controlling temperature changes. Furthermore, as shown in Figure 3, partial temperature changes in the image sensor are caused by A-temperature caused by current flowing through the wiring connecting the image reading element and the image sensor body. The changes shown in the figure occur. There is no fixed method for this measure;
The output signal is stabilized by performing local temperature control using a complicated and large-scale configuration using thermo panels that utilize the Beltier effect.

(Problem to be Solved by the Invention) However, in the conventional example described above, temperature control is performed at multiple locations on the image sensor, so multiple temperature control circuits and temperature control circuits are required, and the configuration is smaller than that of a single image sensor. The possibility that it can be used in various tt parts due to cost etc. decreases. Furthermore, since the configuration is large-scale, there is a possibility that the increase in the number of parts may lead to an increase in the causes of failure. For example, if it is necessary to use multiple line image sensors to operate simultaneously and perform signal processing, the number of control devices and control circuits will be multiplied by the number of chips used, and peripheral devices such as power supplies will also be required. The drawback was that it required countermeasures to counteract the evil shadow VT.

Therefore, in view of the above-mentioned points, an object of the present invention is to suppress changes in image output due to partial or total temperature changes of an image sensor, to simplify the device and reduce costs, and to improve the reliability of the device. An object of the present invention is to provide an image reading device configured to improve the image reading device.

(Means for Solving the Problems) An image reading device according to the present invention includes a first photoelectric conversion element that reads illumination reflected light from a document, an image sensor that reads a second photoelectric conversion element that is shielded from light, and an image sensor that reads illumination reflected light from a document. A signal correction means for correcting image No. 78 outputted from the first photoelectric conversion element by the output signal from the second photoelectric conversion element is provided.

(Function) According to the present invention, the image output signal 43-
i! ! By performing analog calculation (subtraction) using the signal output from the photoelectric conversion element, the image sensor can be controlled partially or completely without the need for temperature control using a large-scale and expensive temperature control circuit. This makes it possible to suppress changes in image output due to temperature changes, simplify the device, reduce costs, and improve the reliability of the device.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an image reading apparatus according to the invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the invention with temperature compensation.

In the figure, +01 is a shift register for sequentially transferring the charge proportional to the amount of light from each photoelectric conversion element to the subsequent amplifier, and 102 is a photoelectric conversion element for converting the image signal into electric No. 43. 103 is a photoelectric conversion element having the same function as the photoelectric conversion element whose light-receiving part is shielded from light; 104 and 105 are each 2 photodiodes;
The two image output signal buffer amplifiers 106 are operational amplifiers for subtracting the image output signal No. 3 and the image output signal No. 1.

The output at the time of nn includes one generated in the photosensitive section and another generated in the transfer section, and the sum of these is output. The dark output is proportional to the operating time of each part, and in the photosensitive part, it is generated under the photodiode and storage electrode, and is proportional to the storage time. In the transfer section, it occurs under the transfer electrode and is proportional to the signal transit time from the input end to the output end of the shift register.

Furthermore, as for the temperature characteristic, the output amount increases as the temperature rises.

Therefore, in this embodiment, temperature drift 1-equivalent Di
The factor that changes the time output is divided by tJF.

As shown in FIG. 1, in this example, two identical characteristics are
image sensors are arranged so that each pixel corresponds to the other. It is assumed that the drive pulses for driving these image sensors are exactly the same, and that each image sensor is housed in the same package.

If a change occurs in the output signal due to a change in temperature or the like after the above conditions are satisfied, the date and time output of the light-shielded photodiode placed near the foot diode for signal reading will also change. In this case, the change in the output from the photodiode for signal reading is caused by the lliff of this photosensitive section.
Since this corresponds to a change in output, it can be easily removed by performing differential calculation (subtraction) on the two output signals.

FIG. 2 shows another embodiment. Here, the number of light-shielded photodiodes is reduced to one-half. If the photosensitive area doubles, the accumulated charge will also double, so the amplifier 205
The gain of is set to l/2.

By doing this, the circuit 41 is made less susceptible to the effects of pixel accumulated charge drop and signal noise.

(Effects of the Invention) As explained above, according to the present invention, in an image sensor having two sets of image reading elements, it is possible to correct the image output signal of the other image reading element by blocking light from one image reading element. As a result, it is possible to reduce costs and improve reliability by simplifying the overall purchasing process. This results in
The dog contributes to reducing the drift of the dark signal due to temperature changes.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a color sensor that is an example of the present invention, Figure 2 is a schematic configuration diagram showing another embodiment of the invention, and Figures 3 and 4 are temperature and temperature diagrams of the color sensor. It is an IJ diagram showing positions and signal states. Shift register, photodiode, light-shielded photodiode, fine gain variable amplifier, differential amplifier. Figure 3 Image sensor drawing (Fig. 4)

Claims (1)

[Scope of Claims] 1) An image sensor having a first photoelectric conversion element that reads illumination reflected light from a document, and a second photoelectric conversion element that is shielded from light; and an image sensor that reads an image signal output from the first photoelectric conversion element. An image reading device comprising: signal correction means for correcting based on the output signal from the second photoelectric conversion element. 2) The image reading device according to claim 1, wherein the image sensor is a color sensor. 3) The image reading device according to claim 1, wherein the image sensor is a line sensor. 4) The image reading device according to claim 1, wherein the image sensor is a CCD image sensor.