JP3168599B2 - Image sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor used for an input section of a facsimile or the like, and more particularly to a light receiving element having two diodes connected in series with opposite polarities in a line. Image formed with light receiving element array
It relates to improvement of a disensor.

[0002]

2. Description of the Related Art An image sensor used for reading an image of a facsimile or the like uses a light-receiving element line having the same length as the width of a document, and electrically scans the document surface in the line direction.
While reading the image signal of the line, the document is moved by the document feeder (sub-scanning direction), and the electrical scanning is sequentially performed to read the entire document surface. In this type of image sensor, for example, as shown in FIG. 5 , a photodiode PD and a blocking diode BD are connected in series so that they have opposite polarities to form one light receiving element 61. Have been proposed in which a plurality of (n) lines are arranged one-dimensionally in a line shape. According to the image sensor having this structure, the light amount from the document surface is in the sub-scanning direction (the direction orthogonal to the line of the light receiving element).
, The operating point between the diodes shifts,
The phenomenon that the photoelectric conversion characteristics have hysteresis occurs.

Reading of an image signal in the sub-scanning direction focusing on one pixel of the light receiving element will be described with reference to FIG . In FIG. 6 , (a), (b) and (c) show the pulse voltage by the shift register SR, the cathode voltage between the diodes,
Each shows an image signal. Further, period B is a period during which the accumulation operation is performed, and period C is a period during which the signal reading operation is performed. The integrator 62 is connected to the anode side of the photodiode PD.
Since it is connected to the input of the (reading circuit), it can be regarded as a virtual ground.

That is, in the signal reading period C, a pulse voltage is applied to the anode side of the blocking diode BD by the shift register SR via the individual drive line 63, and the blocking diode BD is biased in the forward direction, and the cathode between the diodes. The voltage is reset to a nearly constant value. In addition, during the accumulation time B, the photodiode PD is irradiated with reflected light from the original surface (not shown), and a photocurrent proportional to the amount of irradiation of the light flows into the anode side of the photodiode PD, and the cathode voltage is reduced. Figure
6 Lower (discharge) as shown in (b). The accumulation period B shows the case where the incident light is the maximum, and the accumulation time B 'shows the case where the incident light is negligibly weak. Accordingly, the same amount of charge as the positive charge of the cathode electrode flowing out as a photocurrent during the accumulation period is supplemented (charged) from the outside by the signal reading operation. An image signal output can be obtained by detecting the replenishment of the charge by the integrator 62 via the common signal line 64.

In the above reading operation, if the cathode voltages after the signal reading operation are always the same, the electric charge storing the photocurrent is read by the integrator 62 as it is. However, in actuality, during the signal reading operation, the charging is performed through the internal resistance of the blocking diode BD, so that the cathode voltages after the signal reading operation are not always equal, and the integrator 6 is not charged.
2 produces an error. This error has a small value when the light amount is constant, but has a non-negligible value when the light amount changes abruptly, for example, at the boundary between black and white patterns existing in the sub-scanning direction. This phenomenon is a kind of hysteresis phenomenon (history phenomenon) based on the history of the black-and-white pattern that has been read so far, particularly when the light output suddenly increases from the dark output state to the bright output state. When the dark output state occurs due to a sharp decrease in the amount of light, it appears remarkably.

In view of the above, an image sensor having a structure in which a light source for directly irradiating the photodiode PD is provided and the photodiode PD is exposed to light by the light source by the light source prior to reading an image signal to perform idle reading is proposed. Have been. According to this image sensor, after the photocurrent is accumulated under a constant incident light, the idle reading is performed, so that the cathode voltage between the diodes can be made substantially constant. This makes it possible to eliminate or reduce the hysteresis (see Japanese Patent Application Laid-Open No. 58-127465).

[0007]

However, according to the above-mentioned image sensor, since the blank reading is performed for each line for reading the image signal, the time required for reading the document is doubled and the reading speed is reduced. There was a problem.

The present invention has been made in view of the above circumstances, and has as its object to provide an image sensor that improves the sensitivity of a light receiving element without increasing the reading time of a document.

[0009]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
According to the first aspect of the present invention, the polarity of the two diodes is reversed.
Connect, photodiode on one side, blocking on the other
Multiple light receiving elements configured as diodes in a line
A light receiving element array is formed side by side, and
Connect the photodiode end to the common wiring connected to the reading circuit.
And the blocking diode of each light receiving element
Read image signal by applying read pulse sequentially to side edge
A reading circuit for each of the light receiving elements.
Charge accumulation due to photocurrent in the side photodiode
Bias light before and throughout the reading period with time and charge
An irradiation means for irradiating the blocking diode is provided.
It is characterized by: Also, the invention of claim 2
Item 2. The image sensor according to Item 1, wherein the blockin
Bias light to the photodiode,
The bias light quantity at both ends of the
It is characterized by providing a light amount adjustment plate that adjusts
are doing.

[0010]

According to the first aspect of the present invention , a substantially constant amount of bias light is applied to the blocking diode during the charge accumulation period due to photocurrent in the photodiode on the reading circuit side and the reading period due to the charging period. Can be maintained at a substantially constant value. Further, the image signal of the document can be obtained by calculating the difference between the signal output of the image sensor and the signal output of the image sensor when only the bias light is irradiated.
Further, according to the invention of claim 2, it is possible to provide a light quantity adjusting plate.
As a result, a fluorescent light source was used as a bias light source.
Even in the case, blocking on both ends of the light receiving element array
The same amount of bias light is applied to the diode as the center.
Can be done.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image sensor according to an embodiment of the present invention will be described with reference to FIG. The light receiving element array which is long in the front and back direction of the figure is composed of a light receiving element 2 in which a photodiode PD and a blocking diode BD are connected in series with opposite polarities on an insulating substrate 1 along the front and back directions. And a plurality of them are arranged.

Each light receiving element 2 has a metal electrode 11 made of chromium or the like and discretely arranged on an insulating substrate 1 made of glass or the like, and hydrogenated amorphous silicon (a-Si; H).
A band-shaped photoelectric conversion layer 12 made of, and a band-shaped transparent electrode 13 made of indium tin oxide or the like are sequentially laminated and patterned.
To form a photodiode PD and a blocking diode BD. The photodiode PD and the blocking diode BD are connected in series in a state where the polarity is reversed by using the same metal electrode 11 on the cathode side. The photodiode PD and the blocking diode BD are covered with an insulating layer 14 of polyimide or the like, and lead wires 16 made of aluminum or the like are passed through the contact holes 15 formed in the insulating layer 14 by a photolithography method. 17 respectively. The insulating layer 14 is patterned so as to have an opening 18 on the photodiode PD and the blocking diode BD, and has a structure in which light can enter the photodiode PD and the blocking diode BD.

Leader wiring 1 on the photodiode PD side
6 is an integrator 6 via a common signal line 64 shown in FIG.
2, and the lead-out line 17 on the blocking diode BD side is connected to the shift register SR via the individual drive line 63, and a read pulse is applied from the shift register SR.

On the photodiode PD, a selfoc lens 19 as an equal-magnification image forming lens is arranged. A fluorescent light source 21 for irradiating the original 20 is arranged on the side of the selfoc lens 19. The fluorescent lamp light source 21 is arranged so as to irradiate the surface of the document 20 and to apply bias light to the blocking diode BD. Irradiation of a substantially constant amount of light by the bias light is always performed throughout the period of accumulating electric charges by the photocurrent in the photodiode PD by the reflected light from the surface of the document 20, and the period of reading the image signal by recharging. In order to prevent light leakage, a semi-cylindrical light shielding member 22 is provided on the side opposite to the selfoc lens 19.

The fluorescent light source 21 is adjusted so that sufficient illuminance can be obtained on the surface of the document 20. Therefore, if the light from the fluorescent lamp light source 21 is used as it is as the bias light, the illuminance is too large, so that the light amount adjusting plate 23 is arranged and fixed between the fluorescent lamp light source 21 and the blocking diode BD.

As shown in FIG. 2, the light amount adjusting plate 23 has
Many holes are provided in the rectangular plate. The holes are formed by a plurality of rows of hole arrays 24 having the same pitch and different sizes, and the holes of the hole array 24 are formed from the one long side 23a of the light amount adjusting plate 23 to the other long side 23a (sub scanning direction). Are formed so as to be sequentially smaller. In addition, each hole array 2
The hole constituting 4 is formed so as to be small at the central portion and gradually increase as approaching the short side 23b of the light amount adjusting plate 23. The reason why the holes of the hole array 24 are changed along the sub-scanning direction is that a slide mechanism (not shown) capable of moving the light amount adjusting plate 23 in the sub-scanning direction is provided, and the light amount adjusting plate 23 is blocked by the mechanism. This is because the amount of light passing through the diode BD can be adjusted. However, the hole array 24 does not correspond to the blocking diode BD array in a one-to-one correspondence, and light is emitted from the plurality of hole arrays 23 to the blocking diode BD array. Also, the reason that the holes constituting each hole array 24 are made larger as approaching the shorter side 23b is that, in the fluorescent light source 21, in consideration of the characteristic that the amount of light from both ends decreases, the light receiving element array This is to irradiate the same amount of light as in the central portion also in the blocking diode BD at the end.

Further, as another embodiment of the light amount adjusting plate 23, the holes formed in the light amount adjusting plate 23 are all the same in size, and the light amount adjusting plate 23 has one long side 23a to the other long side 23a side. In the (sub-scanning direction), the density of hole formation is reduced, and in each hole array 24, the density of the center portion is low and the density is increased as approaching the short side 23b side of the light amount adjusting plate 23. You may.

According to the above embodiment, the light emitted upward from the fluorescent lamp light source 21 is reflected on the surface of the document 20, and the reflected light is guided to the photodiode PD via the selfoc lens 19. On the other hand, the amount of light emitted downward from the fluorescent lamp light source 21 is adjusted by the light amount adjusting plate 23, and 10 to 30% of the light amount of the fluorescent lamp light source 21 is guided to the blocking diode BD side as bias light.

According to the image sensor without irradiation of the bias light, when the amount of light incident on the photodiode PD is extremely small, the data is read from the shift register SR to the blocking diode BD via the lead-out wiring 17. Each time a pulse is applied, the cathode voltage between the diodes increases. When a certain amount of light enters after the cathode voltage rises, the cathode voltage is reset only to the value before the rise even if a read pulse is applied. The rise is an error in the output signal. In this embodiment, the blocking diode BD
Is constantly irradiated with bias light, and even when there is no reflected light from the surface of the document 20 (dark output), photocurrent is accumulated in the blocking diode BD under the bias light. A reading pulse is applied to the blocking diode BD to recharge the photo diode PD, so that the diode is independent of the history of the original pattern.
The cathode voltage between the nodes can be maintained at a substantially constant value.

An image sensor having a structure in which the photodiode PD and the blocking diode BD are connected in series as described above is manufactured at a low cost.
The PD and the blocking diode BD are simultaneously manufactured by a thin film process. Therefore, the same material is used for the semiconductor layer 12. Photo diodes such as amorphous silicon
The semiconductor layer used as the semiconductor layer of the PD has good characteristics as a photodiode for performing photoelectric conversion, but has insufficient response as a switch. According to the present embodiment, the blocking diode BD is always irradiated with the bias light, so that the switching characteristics of the blocking diode BD can be improved.

Further, according to the present embodiment, the bias light is obtained from the fluorescent lamp light source 21 by providing the light amount adjusting plate 23, so that it is not necessary to provide a light source dedicated to the bias light, and the device can be manufactured at low cost. .

When an original is actually read, as shown in FIG. 3, an AD converter 31 connected to the image sensor 30 (the output of the integrator 62 in FIG. 6) and the AD converter 31
A digital arithmetic unit 32 which receives a signal from the A / D converter and outputs an image signal; a dark output RAM 33 and a bright output RAM 3 which store a dark output signal and a bright output signal from the AD converter 31;
4 is used. And
Before the original is sent to the image sensor 30, the dark output signal (output when only the bias light is irradiated) is read by making the original cover black or the like, and stored in the dark output RAM 33. -When the output of the sensor 30 (the output at the time of irradiation of reflected light and bias light from the original) is read, the image signal on the original original surface is obtained by subtracting the dark output signal in the digital calculator 32. be able to. The bright output RAM 34 is a storage device for performing shading correction.

FIG. 4 shows another embodiment of the present invention.
Fluorescent lamp light source 4 dedicated to bias light separately from fluorescent lamp light source 21
1 is provided. Parts having the same configuration as in FIG. 1 are denoted by the same reference numerals. The light from the fluorescent light source 41 is adjusted to be suitable as bias light. Fluorescent light source 4
Light emitted from 1 is incident on a photodiode PD and a blocking diode BD. The light from the fluorescent light source 21 for irradiating the original 20 is directly transmitted to the photodiode PD and the blocking diode BD.
The light shielding member 22 'is arranged so as not to enter the light. Therefore, the photodiode PD and the blocking diode BD are constantly irradiated with the bias light, and even when there is no reflected light from the surface of the original document 20 (dark output), the photodiode is still under the bias light. Photocurrent is accumulated in the PD and the blocking diode BD,
Thereafter, a reading pulse is applied to the blocking diode BD to recharge the photodiode PD, so that the cathode voltage between the diodes is maintained at a substantially constant value regardless of the history of the original pattern. can do.

[0024]

[0025]

According to the present invention, throughout the period of reading by the accumulation period and the charging period of the charge due to the photoelectric current in the photo-da <br/> diode reading circuit side, irradiates the bias light of substantially constant light intensity in the blocking diode Therefore, the cathode voltage between the diodes can be maintained at a substantially constant value. Therefore, by obtaining the difference between the signal output of the image sensor and the signal output of the image sensor when only the bias light is applied, an image signal faithful to the original image can be obtained, and the performance of the image sensor is improved. be able to. Also, bias light is applied to the blocking diode.
The blocking diode is switched on
The characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of an image sensor according to an embodiment of the present invention.

FIG. 2 is an explanatory plan view of the light amount adjusting plate of FIG. 1;

FIG. 3 is a block diagram of the image reading apparatus.

FIG. 4 is an explanatory sectional view of an image sensor showing another embodiment of the present invention.

FIG. 5 shows a photodiode and a blocking diode.
Is an equivalent circuit diagram of an image sensor in which
You.

6 (a), (b) and (c) are views of the image sensor of FIG.
FIG. 4 is a drive circuit diagram showing an operation in a sub-scanning direction in one pixel.
You.

[Explanation of symbols]

1 ... insulating substrate, 2 ... light receiving element, 11 ... metal electrode,
12: photoelectric conversion layer, 13: transparent electrode, 16: lead-out wiring, 17: lead-out wiring, 20: manuscript, 21 ...
Fluorescent light source, 23: light intensity adjustment plate, 24: hole array,
PD: Photodiode, BD: Blocking diode.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/024-1/036 H04N 1/04-1/207

Claims (2)

(57) [Claims] 1. Two diodes connected in reverse polarity
One on the photodiode and the other on the blocking die.
The light-receiving element configured as a diode by arranging a plurality linearly to form a light-receiving element array, Fotoda of the respective light receiving elements
In an image sensor for connecting an ion side end to a common wiring connected to a reading circuit and sequentially applying a reading pulse to a blocking diode side end of each light receiving element to read an image signal, the reading circuit side of each light receiving element The bias light is applied to the blocking diode during the charge accumulation time due to the photocurrent in the photodiode and the reading period due to the charge.
An image sensor comprising an irradiation unit for irradiating. 2. The device according to claim 1, further comprising:
The bias light at both ends of the light receiving element array
Light amount adjusted so that is larger than the inner bias light amount
The image sensor according to claim 1, further comprising an adjustment plate.