JPH0575787A - Photoelectric converter - Google Patents

Abstract

PURPOSE:To increase an MTF (modulation transfer function) in the subscanning direction sufficiently high even when an original read speed (that is, original feed speed) is high. CONSTITUTION:Only part of an area to be read depending on a critical angle of an original luminous flux propagating through a transparent protection member placed on a photoelectric conversion element 101 in the photoelectric converter is lighted by a luminous flux. Thus, e.g. a light shield layer 103 is expanded to leave only a part between adjacent photoelectric conversion elements 101 is left as a window 102.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device for converting an optical image into an electric signal, and more particularly to a photoelectric conversion device used for an input unit such as a facsimile, an image reader, a digital copying machine and an electronic blackboard.

[0002]

2. Description of the Related Art In recent years, in order to reduce the size and improve the performance of facsimiles, image readers, etc., a long line sensor having an equal magnification optical system has been developed as a photoelectric conversion device.

Further, for downsizing and cost reduction, a photoelectric sensor in which an image sensor directly detects reflected light from an original through a transparent spacer such as glass without using a 1 × fiber lens array (rod lens array). Conversion devices have also been proposed.

FIG. 1 and FIG. 2 are cross-sectional views schematically showing a conventional photoelectric conversion device as described above, which the applicant of the present invention has previously proposed. FIG. 1 is a schematic cross-sectional view of a photoelectric conversion element array of a conventional photoelectric conversion device as viewed from the main scanning direction,
FIG. 2 is a schematic cross-sectional view of the photoelectric conversion element array as seen from the sub-scanning direction.

Here, 1 is a translucent sensor substrate, which is a photoelectric conversion element (for example, a CCD array) formed by a semiconductor process or the like on a translucent substrate such as glass, an illumination window, a charge storage capacitor, It has a switching transistor and the like. Reference numeral 1'denotes a translucent protective member that covers the translucent sensor substrate 1. Reference numeral 2 denotes a translucent mounting substrate, which has a wiring portion 4 formed on a translucent substrate such as glass by a thick film printing method or a photolithography method. The wiring portion 4 electrically connects the translucent sensor substrate 1 and a drive circuit portion (not shown). Then, the translucent sensor substrate 1 is adhered onto the translucent mounting substrate 2 with the adhesive layer 5. Reference numeral 3 is a light source for illuminating the original 6, and is composed of an LED array in which a plurality of LED (light emitting diode) chips are arranged in an array. The original 6 is placed on the translucent protective member 1'in close contact with or in close proximity to it through a thin air layer. The reading position of the original 6, the arrangement position of the illumination windows of the translucent sensor substrate 1, and the optical axis of the light source 3 in the array direction are set at positions such that they are in a vertical plane lowered from the reading position of the original 6. Has been done.

FIG. 3 is an enlarged view of the pattern formed on the translucent sensor substrate 1 in the vicinity of the photoelectric conversion element. In the figure, 101 is a photoelectric conversion element, and 102 is an illumination window. The illumination window 102 is a portion a sandwiched by the photoelectric conversion elements 101.
And the other part b. A light shielding layer 103 is provided between the photoelectric conversion element 101 and the translucent sensor substrate, and prevents light from the light source from directly entering the photoelectric conversion element 101.

In the above structure, as shown in FIG.
Illumination light from the light source 3 is transmitted through the translucent mounting substrate 2 and the illumination window 102 in the translucent sensor substrate 1 to illuminate the document 6, and the information light reflected from the document 6 is transmitted through the translucent sensor substrate 1.
When incident on the photoelectric conversion element 101, the photoelectric conversion element 10
1 is converted into an electric signal. Each photoelectric conversion element 101
Is output as a time-series signal by a drive circuit unit (not shown).

Next, the operation of the photoelectric conversion element for converting into an electric signal and reading will be described with reference to the circuit diagram of FIG. 4, focusing on a certain photoelectric conversion element. In the figure, S is the photoelectric conversion element of interest, C ₁ is a charge storage capacitor, and ST
Reference numerals ₁ and ST ₂ are switching transistors connected in series with the photoelectric conversion element of interest, C ₂ is a reading capacitor, and A is a reading amplifier. S ', S "
Are photoelectric conversion elements other than the photoelectric conversion element of interest, and a charge storage capacitor, a switching transistor, etc., which are peculiar to each of them, are connected to them, but are omitted for simplification.

First, when the photoelectric conversion element S is illuminated with the brightness of the illuminance E due to the incidence of light, its resistance value changes, whereby the photocurrent I flows and the charge is stored in the charge storage capacitor C _1. It After the predetermined charge storage time, the switching transistor ST ₁ is turned on, so that the charges stored in the capacitor C ₁ are transferred to the subsequent capacitors C ₂ and sequentially read through the amplifier A. After that, the switching transistor ST ₁ is turned on once, the residual charge of the capacitor C ₁ is discharged, and then the switching transistor ST ₁ is turned off again, and the accumulation of the signal charge for the next reading is started.

In the photoelectric conversion device as described above, in order to obtain a high quality image, it is necessary to have a capability of clearly reading thin lines and fine characters written on a document without being crushed. Is desirable. An MTF (modulation transfer function) value is used as an index for evaluating this reading ability. The MTF value is evaluated using the contrast ratio between the output corresponding to the white stripes and the output corresponding to the black stripes when a test original having a pattern of fine black and white stripes is usually used.

In order to measure the MTF value in the main scanning direction, the test original is placed with its striped pattern oriented orthogonally to the main scanning direction, and the photoelectric conversion element is used for reading. At this time, since each photoelectric conversion element alternately faces the white stripe portion and the black stripe portion of the pattern, the contrast ratio of these signals may be taken.

In order to measure the MTF value in the sub-scanning direction, the test original is placed with its striped pattern parallel to the main scanning direction, and the original is fed by the original feeding roller little by little and photoelectrically transferred. Read with the conversion element. At this time, the photoelectric conversion element faces the white stripe portion and the black stripe portion of the pattern one after another as the document is fed, but opposes the signal output and the black stripe portion when facing the white stripe portion. The contrast ratio of the signal output at that time may be taken.

The MTF value in the main scanning direction is determined by superimposing optical factors such as the sharpness of the original image projected on the photoelectric conversion element and electrical crosstalk of the output from each photoelectric conversion element. On the other hand, the MTF value in the sub-scanning direction is determined by superimposing the above-mentioned optical factors and other factors such as the photoresponsiveness of the photoelectric conversion element and the matching between the document feeding operation and the signal charge accumulating operation.

In the photoelectric conversion device having a relatively slow original reading speed, which has been used conventionally, in the sub-scanning direction M
The photoresponsiveness of the photoelectric conversion element with respect to the TF value and the influence of the document feeding operation were small and could be ignored.

[0015]

In recent years, as the performance of facsimiles, image readers and the like has improved, there has been a demand for higher document reading speed. However, in the photoelectric conversion device as in the above-described conventional example, when the document reading speed is increased, there is a problem that the MTF in the sub-scanning direction is particularly lowered.

In order to study this problem in more detail, the transition of the illuminance on the photoelectric conversion element surface and the photocurrent I associated with the feeding of the original will be traced by focusing on one photoelectric conversion element.

As described above, the test original is subjected to MTF in the sub-scanning direction.
When the setting is made for measuring the value and sending, the photoelectric conversion element S of interest opposes the white stripe portion and the black stripe portion of the pattern one after another as the document is sent. Accordingly, the illuminance on the target photoelectric conversion element S surface also changes one after another. Illuminance E at this time
FIG. 5 shows transitions of the photocurrent I, the amount of electric charge Q stored in the storage capacitor C ₁ , and the signal output from the photoelectric conversion element read by the amplifier A.

Here, document feeding by a document feeding roller (not shown) is ideal. When a document feeding pulse is sent, the roller is momentarily moved slightly to feed a small amount of the document, and thereafter, It shall be stationary until the document feed pulse is sent. Further, the document feed amount for each time is the same as the width of the white stripes and the width of the black stripes, and the phase of the document feed is correct. For example, if the document feed is performed once after reading the black stripes, It is assumed that the next white stripe is exactly at the reading position of the photoelectric conversion element S.

As shown in FIG. 5, a small amount of the document is fed at time T ₁ , and the white stripe portion comes to the reading position of the photoelectric conversion element S of interest. Illumination of the photoelectric conversion element surface rises from E _b to E _a. Along with this, the photocurrent I also rises.
The rising of the photocurrent I is generally accompanied by some delay due to the characteristics of the photoelectric conversion element and the like, but eventually reaches _a stable photocurrent I _a at the illuminance E _a . In this state, the signal charge is accumulated in the capacitor C ₁ , and after the predetermined accumulation time τ has elapsed from the time T ₁ , the switching transistor ST
₁ turns ON.

The charge Q _a accumulated in the capacitor C ₁ is transferred to the read capacitor C ₂ and then read by the amplifier A, and the output a corresponding to the charge Q _a appears at the output end. Here, q _a in FIG. 5 is a charge that should originally be accumulated but has not been accumulated due to the delay of the rising of the photocurrent.

After that, the capacitors C ₁ and C ₂ are reset, and charge accumulation for the next reading is started again. Around this time, the time is just T ₂ , the document is fed by a small amount again, and the black stripe portion of the document comes to the reading position of the photoelectric conversion element S of interest. Therefore, the illuminance on the photoelectric conversion element surface decreases from E _a to E _b , and the photocurrent I also decreases accordingly. The fall of the photocurrent I also generally involves some delay, but eventually reaches a stable photocurrent I _b at the illuminance E _b . Thereafter, the signal charges are similarly stored, and after the storage time τ has passed from the time T ₂ , the charge Q _b is read out and the output b appears. Here, the charge q _{b in} FIG. 5 is the charge that should have not been stored due to the delay of the fall of the photocurrent, but it should have been stored.

FIG. 6 shows that no pattern is printed,
When a white background paper is used as an original (hereinafter referred to as a white original), and in FIG. 7, a paper on which a solid black is uniformly printed is used as an original (hereinafter referred to as a black original). 4) shows transitions of the illuminance E, the photocurrent I, the accumulated charge Q, and the signal output of the target photoelectric conversion element surface. 6 and 7 vertical axis,
The horizontal axis is common to FIG. 5 described above.

In this case, since the original is a uniform white or black original, the illuminance on the photoelectric conversion element surface (also referred to as sensor surface illuminance) is a constant illuminance E _A or E _B regardless of the original feeding operation. The photocurrent is also a constant photocurrent I _A or I _B
And the accumulated charge is also a constant charge Q _A or Q _B.
Therefore, the output appearing at the output terminal also has a constant value A or B (note that E _A >> E _B , I _A >> I _B , Q _A >> Q).
_B , A >> _B ).

At this time, the sub-scanning direction MTF is

[0025]

[Equation 1]

Is given by

Assuming that there is a linear proportional relationship between the illuminance on the surface of the photoelectric conversion element, the photocurrent, the accumulated charge, and the signal output, the above MTF is

[0028]

[Equation 2]

It becomes

When the document feeding speed is slow, the interval T ₂ -T ₁ for feeding the document by a small amount is large, so that the charge q _a or q _b due to the delay of the rising or falling of the photocurrent is Q _A , It is smaller than Q _B and the second term on the right side of the above equation (2) can be ignored. Therefore, approximately

[0031]

[Equation 3]

It becomes

Next, similar drawings when the document feeding speed is high are shown in FIG. 8, FIG. 9 and FIG. That is, FIG. 8 is for reading a rectangular wave chart of 4 LP / mm (four black line stripes in 1 mm) as an original, FIG. 9 is for reading a white original as an original, and FIG. 10 is for reading a black original as an original. Each case is shown.

In this case, the interval T ₂ -T ₁ for feeding the document by a minute amount becomes very short, and the charge accumulation time τ becomes short accordingly, so that the accumulated charge amounts Q _A , Q _B are low. Significantly reduced compared to the speed case. However, q
_a, the amount of charge represented by q _b is the rise of the photoelectric conversion element, since it is determined by the falling characteristic hardly changed.

Therefore, as shown in the above equation (2)

[0036]

[Equation 4]

The second term on the right side of the above becomes so large that it cannot be ignored, and the MTF decreases.

Further, in order to increase the document feeding speed, it is necessary to shorten the interval for feeding the document by a small amount as described above, but in this case, it becomes difficult to accurately feed the document. That is, in the case of high-speed document feeding, the movement of the document is no longer the ideal intermittent feeding in which the document is momentarily fed and then stopped, and is momentarily fed and then stopped. It is close to the movement.
FIG. 11 shows changes in illuminance, photocurrent, accumulated charge and signal output on the surface of the photoelectric conversion element when reading the rectangular wave chart in this state.

In this case, the illuminance E on the surface of the photoelectric conversion element changes from a rectangular wave shape to a sinusoidal wave shape or a triangular wave shape with respect to time, as shown in FIG. In this case, even if there is no delay in rising or falling of the photoelectric conversion element, the amount of charge q _a ′ that should be accumulated but should not be accumulated or the amount of charge q that is not accumulated but should be accumulated. _b 'is generated, M
TF decreases.

For the reasons described above, in the conventional photoelectric conversion device, when the document feeding speed is increased to increase the document reading speed, MT in the sub-scanning direction is increased.
There was a problem that F was lowered.

Therefore, an object of the present invention is to solve the above-mentioned problems and provide a photoelectric conversion device having a sufficiently high MTF (modulation transfer function) in the sub-scanning direction even when the original reading speed is high. It is in.

[0042]

In order to achieve the above object, the present invention comprises a plurality of photoelectric conversion elements integrally formed on a translucent substrate, and the photoelectric conversion elements are formed in close contact with each other. A photoelectric conversion device having a translucent protective member, which reads an image on a document surface which is arranged in close contact or in close proximity to the translucent protective member via a thin air layer and converts the image into an electric signal. In the above, the means for limiting the illuminated portion for illuminating only a part of the read area determined by the critical angle of the document illuminating light flux traveling through the translucent protection member is provided.

Further, as one mode of the present invention, the illumination portion is limited by the shape of the light shielding layer formed on the plane of the transparent substrate on which the photoelectric conversion element is formed. Can be characterized.

As another aspect of the present invention, the illuminating portion is limited to the light emitting directivity of the illuminating light source, the arrangement of the illuminating light source, the refractive index of the translucent protective member, and the translucent substrate. It can be characterized by limiting the angle of the illumination light flux that travels through the light-transmitting protective member, which is determined by various conditions such as the shape.

As another aspect of the present invention, the peripheral portion of the photoelectric conversion element is covered with the light shielding layer except for the portion between the photoelectric conversion elements adjacent to each other. You can

As another aspect of the present invention, the illumination light source may be arranged at a position other than directly under the photoelectric conversion element.

[0047]

According to the present invention, the original illuminating light flux illuminates only a part of the area to be read which is determined by the critical angle of the original illuminating light flux traveling in the translucent protection member provided on the photoelectric conversion element. Since it is configured, the MTF deterioration due to optical factors is suppressed, and thus the MTF in the sub-scanning direction becomes sufficiently high even when the document reading speed is high.

[0048]

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

FIG. 12 is an enlarged view in the vicinity of the photoelectric conversion element of the pattern formed on the translucent sensor substrate in the photoelectric conversion device of the first embodiment of the present invention. In the figure, 101 is a photoelectric conversion element, 102 is an illumination window, and 103 is a light shielding layer. Compared with the above-described conventional example shown in FIG. 3, in this example, the light shielding layer 103 is expanded, and the photoelectric conversion elements 10 adjacent to each other are provided.
It can be seen that only the portion between 1 is left as a window.

FIG. 13 shows the optical path of a light ray in the present embodiment, and FIG. 14 shows the conventional in-plane light ray passing through the cutting line AA ′ in FIG. 12 or the cutting line BB ′ in FIG. A schematic diagram is shown. In the figure, 1 is a translucent sensor substrate, 1'is a translucent protective member on the substrate 1, 3 is a light source, and 6 is an original. The surface of the original 6 is illuminated by the illumination light from the light source 3, and the light flux reflected there enters the photoelectric conversion element 101. However, the reflected light from the outside of the read area RA determined by the critical angle θ _C of the light flux in the translucent protection member 1 ′ does not enter the photoelectric conversion element 101.

In the conventional example shown in FIG. 14, the illumination window 102 is used.
Is large, the entire area RA to be read is illuminated with illumination light.

On the other hand, in the present embodiment shown in FIG. 13, since the illumination window 102 is narrowly limited, only a portion LA in the read area RA is illuminated by the illumination light, and the read target is substantially read. The area RA 'becomes much narrower than in the conventional example. As a result, in the present embodiment, unnecessary wraparound light is prevented from entering the photoelectric conversion element 101, and thus it is possible to prevent the optical MTF from decreasing during high-speed document reading.

(Other Embodiments) FIG. 15 is an enlarged view of the pattern on the transparent sensor substrate in the photoelectric conversion device of the second embodiment of the present invention in the vicinity of the photoelectric conversion element. In the figure, reference numerals are the same as those in FIG. Also, the cutting line C- in FIG.
FIG. 16 is a schematic diagram showing the optical path of a light ray in a plane passing through C'and perpendicular to the plane of the drawing.

In the present embodiment, the light shielding layer 103 is expanded so as to cover one side portion of the illumination window, which has spread to both sides of the photoelectric conversion element 101 in the conventional example of FIG. 3, as shown in FIG. Further, the light source 3 is not directly below the photoelectric conversion element 101 as shown in FIG. 16, but is inclined and arranged so as to illuminate the photoelectric conversion element 101 obliquely. Therefore, the illumination light of the light source 3 illuminates only a part LA of the read area RA on the surface of the document 6, and the overlapping portion of the illuminated area LA and the read area RA is substantially the read area RA '. Becomes As a result, in the present embodiment, as in the first embodiment described above, the read area RA 'is substantially narrowed and the optical MTF is improved.

As described above, according to the embodiment of the present invention, since the optical MTF is improved, the illuminance of the optical conversion element surface at the time of reading the white stripe of the test document and the illuminance at the time of reading the black stripe. Is higher than that of the conventional example, and even when a document is sent at high speed for reading, the contrast of the output signal of the photoelectric conversion device is high and a sufficient value of MTF can be obtained.

[0056]

As described above, according to the present invention,
Since only a part of the area to be read, which is determined by the critical angle of the document illumination light flux traveling through the translucent protection member that covers the photoelectric conversion element, is illuminated, deterioration of the optical MTF is suppressed, thereby reading the document. Even if the speed is high, it is possible to obtain a photoelectric conversion device having a sufficiently high MTF in the sub-scanning direction.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a configuration of a conventional photoelectric conversion device from a main scanning direction.

FIG. 2 is a schematic cross-sectional view of the conventional apparatus of FIG. 1 viewed from the sub-scanning direction.

FIG. 3 is an enlarged view of a pattern formed on the conventional translucent sensor substrate of FIGS. 1 and 2 in the vicinity of a photoelectric conversion element.

FIG. 4 is a circuit diagram showing a circuit configuration for reading an electric signal from the photoelectric conversion element of FIG.

FIG. 5 is a diagram showing the illuminance of the conventional photoelectric conversion element surface of interest when a test document of a rectangular wave chart is read using the circuit of FIG.
FIG. 6 is a waveform diagram showing a transition of a photocurrent, a charge amount stored in a charge storage capacitor, and a signal output read by an amplifier.

[Figure 6] White paper with nothing printed on it is the original (white original)
FIG. 7 is a waveform diagram showing the transition of the illuminance and the like on the conventional photoelectric conversion element surface in such a case.

FIG. 7 is a waveform diagram showing changes in the illuminance and the like on the conventional photoelectric conversion element surface when a document (black document) on which solid black is uniformly printed is used as a document.

FIG. 8 is a waveform diagram showing changes in illuminance and the like of a conventional theoretical photoelectric conversion element surface when reading a test document of a rectangular wave chart when the document feeding speed is fast.

FIG. 9 is a waveform diagram showing a transition of illuminance and the like on a conventional photoelectric conversion element surface of interest when a white original is read at a high original feeding speed.

FIG. 10 is a waveform diagram showing a transition of illuminance and the like on a conventional photoelectric conversion element surface of interest when reading a black original when the original feeding speed is fast.

FIG. 11 is a waveform diagram showing a transition of the illuminance and the like of a conventional practical photoelectric conversion element surface when reading a test document of a rectangular wave chart when the document feeding speed is fast.

FIG. 12 is an enlarged view in the vicinity of a photoelectric conversion element of a pattern formed on a translucent sensor substrate of the photoelectric conversion device according to the first example of the present invention.

FIG. 13 is a section line A- in the embodiment of the present invention shown in FIG.
It is a schematic optical-path figure showing the optical path of the light ray in a surface which passes A'and is perpendicular to the paper surface.

FIG. 14 is a schematic optical path diagram showing an optical path of a light ray in a plane which passes through a cutting line BB ′ in the conventional example of FIG. 3 and is perpendicular to the paper surface.

FIG. 15 is an enlarged view in the vicinity of a photoelectric conversion element of a pattern formed on a translucent sensor substrate of a photoelectric conversion device according to a second example of the present invention.

16 is a cutting line C- in the embodiment of the present invention of FIG.
It is a schematic optical-path figure showing the optical path of the in-plane light ray which passes C'and is perpendicular | vertical to a paper surface.

[Explanation of symbols]

1 translucent sensor substrate 1 'transmissive protecting member 2 translucent mounting board 3 source 4 wiring section 5 adhesive layer 6 original 101 photoelectric conversion element 102 illumination window 103 light-shielding layer S interest photoelectric conversion elements C _1, C ₂ capacitors ST ₁ , ST ₂ switching transistor A readout amplifier

Claims (5)

[Claims] 1. A light-transmitting substrate comprising: a plurality of photoelectric conversion elements integrally formed on a light-transmitting substrate; and a light-transmitting protective member formed in close contact with the photoelectric conversion elements. A photoelectric conversion device for reading an image on a document surface arranged in close contact or very close to a protective member via a thin air layer and converting the image into an electric signal, the original illumination traveling through the translucent protective member. A photoelectric conversion device comprising means for limiting an illuminating part for illuminating only a part of a read region determined by a critical angle of a light beam. 2. The illuminating portion is limited by the shape of a light shielding layer formed on a plane of the light transmissive substrate on which the photoelectric conversion element is formed. The photoelectric conversion device described in 1. 3. The limitation of the illuminating portion is determined by various conditions such as the light emission directivity of the illuminating light source, the arrangement of the illuminating light source, the refractive index of the translucent protective member, and the shape of the translucent substrate. The photoelectric conversion device according to claim 2, wherein the photoelectric conversion device is formed by limiting an angle of an illumination light flux that travels through the translucent protection member. 4. The photoelectric conversion device according to claim 3, wherein a peripheral portion of the photoelectric conversion element is covered with the light shielding layer except a portion between the photoelectric conversion elements adjacent to each other. .. 5. The photoelectric conversion device according to claim 3, wherein the illumination light source is arranged at a place other than directly below the photoelectric conversion element.