JPS639357A - Image sensor and information input device using same - Google Patents

Abstract

PURPOSE:To obtain a stable read output with fidelity to information to be read independently of environmental change such as temperature change by shading one bit of sensors arranged for plural number, using the shaded bit as a reference bit so as to obtain a read output at the dark state at all times and using it as a reference thereby correcting the output. CONSTITUTION:Sandwich-shaped sensors S1-SN are arranged in a line on a board 101, an electric charge stored in a charge storage capacitor C is amplified by an amplifier A and its output is outputted sequentially via analog switches W1-WN driven by a shift register R. A read section 20 shielding a 1st sensor S1 with a shading film to obtain a reference bit, and a signal processing circuit section 300 holding the output of the sensor S1 in a hold capacitor Ch via a sampling switch SW to correct the output of each sensor sequentially based on the signal level by means of a differential amplifier As are provided. Then the read signal output V0 is outputted and the photoconductive layer 104 of only the sensor S1 is covered by a light shield film 106 and each photodetecting region is specified by a light receiving window 0 for the other sensors.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image sensor, and to an information input device using the same.

[Prior art and its problems]

A contact image sensor that uses a long reading element with a sensor section that is the same width as the document is made of amorphous silicon (
By using an amorphous semiconductor such as a-Si) or a polycrystalline thin film such as cadmium sulfide (CdS) or cadmium selenide (CdSe) as a leading conductor layer,
It is a device that is being put into practical use and is attracting attention as a large-area device that does not require a reduction optical system, as there is a demand for miniaturization of document reading devices.

One of the basic structures of this image sensor is a sandwich type sensor. As shown in FIGS. 4(a) and 4(b), this sandwich type sensor has a photoconductor layer 4 sandwiched between a lower electrode 2 formed on a substrate 1 and a transparent upper electrode 3. In the case of a contact type image sensor, a plurality of these sandwich type sensors are mounted on a long substrate (for example, in the case of 8 dots/IIIm, Japanese Industrial Standard A is used).
1728 pieces for column 4 and 2048 pieces for same view IB column 4) are arranged in parallel.

The driving methods for such image sensors include an accumulation type that uses only the primary photocurrent generated by light irradiation, a photoconductive type that uses a secondary photocurrent, and a scanning circuit. They are classified into direct drive type and matrix drive type based on the connection method.

FIG. 5 is an equivalent circuit diagram showing part of the circuit configuration of a contact type image sensor using an accumulation type and a direct drive type.

This circuit generates a charge storage capacitor C (combined capacitance C of the element capacitance and peripheral circuit capacitance) by the photocurrent ■ of each photoelectric conversion element S+' to S' consisting of a sandwich type sensor.
Each amplifier A amplifies the charges accumulated in the amplifier A, and the output thereof is sequentially outputted via an analog switch W driven by a shift register R. Here, CK indicates a clock input, and IA indicates a shift register start pulse.

In such a circuit, the output signal level V obtained from each sensor is equal to the current from the sensor! S and input leakage current 1
g is expressed by the following formula.

= (I +1) - t... (1) C: Capacity of charge storage capacitor t: Time By the way, when the sensor current at the time of withdrawal is 1 -1 and the sensor current at the time of dark P is 18-I, When the substrate temperature changes due to a change in the environmental temperature, the sensor current in the dark changes significantly as shown in FIG. In the figure, the vertical axis is (logl (1-1p).

I, I, ), and the horizontal axis is the substrate temperature Ta ('C).

That is, the output signal is output as shown in Fig. 7, with V at the time of withdrawal and V at the time of darkness, but as is clear from Fig. 6, the output signal level at the time of darkness changes depending on the temperature. . In particular, the change in the dark current (1) changes significantly when the temperature dd (usually 70 to 80°C) is higher than the intersection of I and -1g.

By the way, when reading a halftone image, for example, output signal gradation processing is normally performed using a specific level as a threshold, but changes in the output voltage in the dark, that is, the dark voltage, cause reading errors, and there is a difference in the read image. There is a problem in that it is difficult to reproduce faithful gradation density.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to perform faithful and stable reading of images without depending on changes in the external environment such as temperature changes.

[Means for solving problems]

Therefore, in the image sensor of the present invention, one bit of the plurality of sensors arranged on the substrate is shielded from light so that this bit always outputs a dark voltage.

Further, in the information input device using the image sensor of the present invention, one of the plurality of sensors arranged on the substrate is
The bit is shielded from light and used as a reference bit, a reference level determined based on the output voltage of the reference bit is held, and the output signal for each bit is corrected based on this reference level.

[Effect]

That is, in the present invention, one bit of the sensor in the long reading element is shielded from light so that it always emits a dark output signal, and the dark output component is subtracted from the output of each sensor based on this output signal level. By doing so, it is possible to always obtain faithful and stable signal output.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a part of an equivalent circuit showing an information input device using an image sensor according to an embodiment of the present invention.

This information input device has N sandwich-type sensors S1...SN arranged in a row on a substrate, charges accumulated in a charge storage capacitor C are amplified by an amplifier A, and the output is sent to a shift register R. Analog switch W1 driven by
. . . The first bit S1 of these sensors is outputted sequentially via the WN, and the first bit S1 of these sensors is covered with a light-shielding film to serve as a reference bit, and the output of the sensor S1 of the reference bit is sent to a sampling switch. The signal processing circuit section 300 includes a differential amplifier A8 which is held in a hold capacitor Ch via an SW and corrects the output of each sensor in sequence based on this signal level, and outputs a read signal output Vo. It is something.

The main parts of the reading section 200 are shown in FIGS. 2(a) and 2(b).
) and (c), the main parts of which are shown, the glass substrate 10
A hydrogenated amorphous silicon photoconductor layer 104 is formed on the photoconductor layer 104 by a gelom electrode as a lower electrode 102 and a translucent indium tin oxide (ITO) electrode as an upper electrode 103, which are divided and arranged for each bit. A sandwich-type sensor is formed by sandwiching the layers, and the upper layer is further formed with a light-shielding film 106 made of a chromium film having a light-receiving window O for each bit except the first bit, with a passivation film 105 in between. Only the first bit is covered with a light-shielding film, and the light-receiving areas of each of the other layers are defined by the light-receiving window 0.

The output Vo of this information input device and the output T of the reading section
The relationship with out is shown in a timing diagram in FIG.

T out indicates the output of each sensor in the reading section 200 (V is the dark voltage, ■ is the bright pressure), and when this is manually input to the processing circuit section 300, the output of the first bit of the sensor is S/ In synchronization with the sampling pulse shown in H, ■
Hold S/H as shown. This value is set as a reference voltage vDH, and is subtracted from the output of each sensor and output as a correction output Vo.

In this way, the signal output of each line is always corrected based on the output of the first bit (reference bit), so even when the temperature rises, the image to be read remains faithful and stable. You can get the output.

In addition, in the embodiment, the first bit is used as the reference bit, but it is not necessarily limited to the first bit.
A plurality of bits may be used as reference bits. Usually, there are many surplus bits in the drive circuit due to the relationship between the reading width and the drive unit, but it is effective to use these surplus bits as reference bits. Furthermore, the light shielding means is not limited to the chromium film, and may be modified as appropriate, such as by attaching a light shielding seal member.

Furthermore, the present invention can also be applied to a type of image sensor in which the entire surface is the light-receiving surface without defining the light-receiving surface by a light-shielding film. A light shielding film may be formed.

Furthermore, the driving method of the image sensor or the signal processing circuit is not limited to the embodiments, and can be selected as appropriate.

〔effect〕

As explained above, according to the present invention, one bit of a plurality of sensors arranged is shielded from light, and this is used as the base bit so that reading output in a dark state can always be obtained. By correcting the output using this as a reference, it becomes possible to obtain a stable reading output that is faithful to the information to be read, without depending on environmental changes such as temperature changes.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an equivalent circuit of an information manpower device using an image sensor according to an embodiment of the present invention, and FIGS. Figure (b
) and (c) are diagrams showing the basic structure of the A-A cross section and B-B[rilj in FIG. 2(a), respectively, and FIG. FIG. 6 is a diagram showing the relationship between 1B degrees and bright current and dark current, and FIG. 7 is a diagram showing the output of the same sensor. 1.101...Substrate, 2,102...Lower electrode, 3
103... Upper electrode, 4,104... Photoelectric conversion layer, 105... Passivation film, 106... Light shielding layer, 200... Reading section, 300... Processing circuit section, Sl...・SN...sensor, C...charge storage capacitor, A...amplifier, R...shift register, W
1~WN...Analog switch, Ch...Hold capacitor, As...Differential amplifier, O...Light receiving window. Figure 2 (b) Figure 2 (c) Figure 3 Figure 4 (Q) Figure 4 (b)

Claims (4)

[Claims] (1) In an image sensor formed by arranging a plurality of photoelectric conversion elements, one bit of the photoelectric conversion elements is constituted by a light-shielding bit equipped with light-shielding means for blocking light from entering the light receiving section. Featured image sensor. (2) The image sensor according to claim (1), wherein the light shielding means is a light shielding film formed on the light receiving portion of the photoelectric conversion element. (3) The image sensor as set forth in claim (1), wherein the light shielding means comprises a light shielding seal member stuck on the light receiving portion of the photoelectric conversion element. (4) A plurality of photoelectric conversion elements are arranged, and one bit of these photoelectric conversion elements is equipped with a light-shielding means for blocking light from entering the light-receiving section, and is configured as a light-shielding bit as a reference bit that always outputs a dark voltage. What is claimed is: 1. An information input device comprising: an image sensor having the reference bit output as a reference level; and a signal processing circuit that holds the output signal of the reference bit as a reference level and corrects the output of each photoelectric conversion element based on the reference level.