JPH0328872B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color document reading method for improving the color resolution of a color document.

Conventional color document reading devices such as color facsimile machines have used a three-color separation filter consisting of red, border, and blue dichroic mirrors.
The light reflected from the color document by the illumination light source is separated into three colors through a three-color separation optical system consisting of red, edge, and blue dichroic mirrors, and then photoelectrically converted, and an optical signal is converted from the electrical signal. It was used to distinguish colors and read color documents. As described above, since the conventional color document reading apparatus uses a three-color separation filter, a processing circuit and the like for this purpose are also required, which has the disadvantage of complicating the mechanism and circuit configuration of the reading section. Another problem was that the resolution wavelength range was limited by the filter characteristics of the dichroic mirror, making it impossible to obtain sufficient resolution.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a color document reading method that does not require a three-color separation filter as a device, has a simple mechanism, and can obtain efficient resolution results for light in a wide wavelength range. is its purpose.

In view of the above, the present invention focuses on the utilization of elongated thin film reading elements, which have been developed in recent years in order to downsize document reading units such as facsimile machines. This reading element is a multilayered photoelectric conversion element in which a photoconductor is deposited on a plurality of lower electrodes patterned in a predetermined shape on an insulating substrate, and a transparent electrode is further deposited on top of the photoconductor. Such a reading element can be constructed with a size comparable to the width of the document, and not only can it contribute to the miniaturization of the document reading section of facsimile machines, etc., but also has various advantages such as a light response characteristic of 0.1 msec or less and heat resistance of 200 degrees Celsius or more. have.

By the way, when applying the same light to a reading element with such a multilayer structure, if a bias voltage of an arbitrary different value is applied between the lower electrode and the transparent electrode, the value of the photoelectric conversion current obtained by irradiating the light is , which has the property of changing depending on the applied bias voltage. Therefore, in the present invention, the relationship between the ratio of the output value from the photoelectric conversion element and the wavelength when a plurality of different bias voltages are applied while irradiating the same light to the photoelectric conversion element is determined in advance, and then the same light is applied to the photoelectric conversion element. When actual reading scanning is performed under driving conditions, the ratio of the output from the photoelectric conversion element corresponding to the plurality of bias voltages is determined, and the wavelength is determined from this ratio and the relationship between the wavelength and the output ratio determined in advance. I am trying to identify.

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a plan view showing the structure of a color document reading element according to the present invention.
It is constructed by depositing a photoconductor 3 on a plurality of lower electrodes 2 patterned in a comb shape, and further depositing a transparent electrode 4 thereon.

FIG. 2 shows a cross-sectional view of this reading element 5 taken along line A--A. Hereinafter, a method for manufacturing the reading element 5 will be explained in detail based on the actual manufacturing process. In the present invention, glass is used for the insulating substrate 1, Cr is used for the lower electrode 2, amorphous hydrogenated silicon is used for the photoconductor 3, and indium tin oxide is used for the transparent electrode 4. First, Cr (chromium) is deposited on a glass substrate to a thickness of approximately 3000A° using electron beam evaporation. Subsequently, the deposited Cr film is patterned into a plurality of comb shapes by photolithography to form the lower electrode 2. Next, a film of amorphous hydrogenated silicon was deposited to a thickness of about 1 μm using the glow discharge method, and the photoconductor 3
to form. The gas used at this time is 100% SiH ₄
, gas flow rate 20~50SccM, pressure 0.2~
0.5Torr, RF power 20~50W, board temperature 200~300
The preparation conditions were ℃ and film deposition time of 30 minutes to 1 hour. Further, indium tin oxide is deposited on this amorphous hydrogenated silicon to a film thickness of about 1500A by a DC sputtering method to form a transparent electrode 4. In this case, indium tin oxide (90 mol% In ₂ O ₃ + 10 mol%
SnO ₂ ) is used, but the total gas (Ar+O ₂ ) pressure is 1 to 5.
The production conditions are ×10 ^-3 Torr, oxygen partial pressure 1 to 2 ×10 ^-4 Torr, and DC power 150 to 200W. As shown in FIG. 2, the reading element 5 manufactured by such a manufacturing method and under such manufacturing conditions has an n-n type between indium tin oxide, which is the transparent electrode 4, and amorphous silicon hydride, which is the photoconductor 3. It has a so-called photoelectric conversion function that generates a predetermined photovoltaic force by irradiating it with light to form a heterojunction. The lower electrode 2 of the reading element 5 is divided into a plurality of patterns, and the reflected light from the color document can be photoelectrically converted for each pixel by each pattern electrode.

FIG. 3 shows a schematic block diagram of a color document reading apparatus constructed using this reading element 5. As shown in FIG. A switch 6 is connected between the transparent electrode 4 and the ground.
A bias power supply 7 of, for example, -5V is connected via. Further, the lower electrode 2 is connected via a plurality of switches 8 provided corresponding to each lower electrode 2.
It is connected to the signal calculation section 9. Now, the switch 6 is opened and the reading element 5 is uniformly irradiated with light of each wavelength without applying a bias voltage. Then, due to the photoelectric conversion action of the reading element 5, a photocurrent corresponding to the wavelength of each light is generated. At this time, the respective switches 8 connected to the respective lower electrodes 2 are sequentially closed, and the photocurrent _S1 corresponding to each reading element is taken into the calculation section 9, and its value is temporarily stored in a memory (not shown). put. The resulting photocurrent S ₁ for light of each wavelength when there is no bias between the electrodes exhibits the spectral characteristics shown in FIG. 4a. The peak of the spectral characteristics at this time is located around a wavelength of 600 nm. Next, the switch 6 is closed and - is applied between the transparent electrode 4 and the lower electrode 2.
A bias voltage of 5V is applied and light irradiation is performed in the same manner as described above. At this time, by sequentially closing each switch 8 at the same time, the photocurrent _S2 generated in each lower electrode 2 is taken into the calculation section 9. Between these two electrodes -
The photocurrent S ₂ for light of each wavelength obtained at 5V bias exhibits the spectral characteristics shown in FIG. 4b.

It can be seen that the peak of the spectral characteristics at this time has moved to around 460 nm. From this, it can be seen that if a predetermined calculation is performed on the photoelectric conversion currents S ₁ and S ₂ obtained by the method described above, a value that is uniquely determined for each wavelength can be obtained. In the present invention, division is applied to the above calculation. For example, in the normal state, the photocurrent S ₁ obtained when there is no bias between the two electrodes and -5V
The ratio S ₁ /S ₂ to the photocurrent S ₂ obtained during biasing is determined in advance for each irradiation light. FIG. 5 shows the photocurrent ratio S ₁ /S ₂ characteristic when a tungsten lamp is used as the illumination light source. Next, by irradiating light of a certain wavelength, two reading scans are performed, one in a non-biased state and one in a -5V biased state between both electrodes.

In these two reading scans, the signal calculation unit 9
is the photocurrent ratio obtained by a predetermined calculation from the -5V bias photocurrent S ₂ obtained in the subsequent read scan and the non-bias photocurrent S ₁ obtained and stored previously.
Calculate S ₁ /S ₂ and output to output terminal Tout.

By comparing the output of this signal calculation unit 9 with the photocurrent ratio S ₁ /S ₂ determined in advance, the wavelength of the irradiated light can be determined, and from this the color of the light can be determined or read. . In the above example, we have explained the case where the reading element 5 is uniformly irradiated with light of each wavelength experimentally, but when actually installed in a facsimile etc., this irradiated light is reflected from a color original by a light source lamp. It is light.

Therefore, the reading element 5 is irradiated with light corresponding to each pixel of the color original, and the photocurrents S ₁ and S 2 obtained from each lower electrode 2 and the photocurrent ratio S ₁ /S ₂ obtained from the signal calculation section 9 are Different values of S ₂ can be obtained for each electrode. In addition, in the present invention, the photocurrent can be obtained by setting the bias voltage between the lower electrode and the transparent electrode to 0V and -5V.
For S ₁ and S ₂ , we have described an example in which the calculation is performed to find the ratio S ₁ /S ₂ , but if it is possible to find a value that is uniquely determined for each frequency, bias values other than those mentioned above or Of course, calculation may also be used.

As explained above, according to the color document reading method of the present invention, the ratio of the output value from the photoelectric conversion element and the wavelength when a plurality of different bias voltages are applied while irradiating the photoelectric conversion element with the same light. The relationship is determined in advance, and then, when actual reading scanning is performed under the same driving conditions, the ratio of the output from the photoelectric conversion element corresponding to the plurality of bias voltages is determined, and this ratio and the ratio determined in advance are determined. Since the wavelength is determined from the relationship between wavelength and output ratio,
There is no need for a color filter, the mechanism of the reading unit is simplified, and a color document with a high sensor density in a wide wavelength range can be read with one bit, which is an excellent effect.

In the above embodiments, a single layer of amorphous hydrogenated silicon was used as the photoconductor layer, but in addition, the photoconductor layer may have a multilayer structure of metal electrodes/n-type-i-type-p-type a.
-Si:H/transparent electrode and metal electrode with reverse structure/p
A similar effect can be obtained in a sensor having a type-i type-n type a-Si:H/transparent electrode structure.

[Brief explanation of drawings]

1 and 2 are schematic configuration diagrams showing a color document reading element according to the present invention, where FIG. 1 is a plan view and FIG. 2 is a sectional view taken along the line A--A in FIG. 1. FIG. 3 is a schematic circuit diagram of a color document reading device showing an embodiment of the present invention, and FIG. 4 is a graph showing the value of photocurrent for each wavelength of light obtained by the color document reading element of the present invention. is non-biased, b
indicates the time of -5V bias. FIG. 5 is a graph showing the photocurrent ratio S ₁ /S ₂ characteristic when a tungsten lamp obtained by the reading element of the present invention is used as an illumination light source. DESCRIPTION OF SYMBOLS 1... Insulating substrate, 2... Lower electrode, 3... Photoconductor, 4... Transparent electrode, 5... Color original reading element, 6, 8... Switch, 7... Bias electrode, 9... Signal calculation section.

Claims (1)

[Scope of Claims] 1. The relationship between the ratio of output values from the photoelectric conversion element and the wavelength when the same light is irradiated to the photoelectric conversion element and a plurality of different bias voltages are applied is determined in advance, and the photoelectric conversion element is is irradiated with reflected light from a color original, and each of the bias voltages mentioned above is applied to the photoelectric conversion element, the ratio of the output from the photoelectric conversion element to each of the bias voltages is determined, and this ratio and the predetermined wavelength are A method for reading a color original, characterized in that the wavelength of the reflected light is specified from a ratio relationship between the wavelength and the wavelength of the reflected light.