JPS61202561A - Image reader - Google Patents

Abstract

PURPOSE:To attain a large S/N with simple circuit constitution and to obtain the title reader with small size and thin profile by using a differential amplifier to operate a difference between the 1st signal including an image signal and noise obtained via a light receiving element and the 1st switch and the 2nd signal having a noise only obtained via the 2nd switch. CONSTITUTION:Leads of one side of a signal switch 51 are connected respectively to corresponding cathodes of a light receiving element 41 and other leads are connected in common to a bias common line 61. One end of each dummy switch 52 is connected to nowhere, that is, opened and the other leads are connected in common to a dummy common line 62. While anodes of the light receiving element 41 are connected together to a light receiving common line 63. A positive voltage is applied from a bias power 71 so that the light receiving element 41 is reverse-biased to the bias common line 61. Further, an output from the dummy common line 62 and the light receiving common line 63 is inputted to a differential amplifier 72 and an output of the differential amplifier 72 is outputted from an output terminal 73 as a read signal output.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a single image reading device, and more particularly to an image reading device that is used for facsimile and the like and reads a single-size image.

(Prior Art) Generally, an image reading device has light receiving elements arranged in a straight line at intervals equal to the reading resolution.The light receiving elements have the same width as the image to be read, and form an erect, same-size image. The structure is such that the image is read through a focusing lens.

As such a device, Proceedings of the Institute of Image Electronics Engineers 83-04-
1 (High-speed amorphous silicon contact image sensor)
There is something written in.

FIG. 5 is a block diagram showing the configuration of a conventional image reading device. In the figure, reference numeral 11 denotes a light receiving element, which has excellent photoelectric conversion characteristics, manufacturability, and stability.

When operated in the charge accumulation mode that caused the high and low resistance,
It is made of amorphous silicon (hereinafter abbreviated as a-3i) which also provides a high optical response speed. Reference numeral 12 denotes a switch element, which is composed of, for example, an MO8 type FET. 13 is an integrator that converts the sawtooth waveform generated from the switch element 12 into a square wave. Sample and hold circuits 14 and 15 output pulse signals corresponding to two consecutive pulses (double pulses) to each of the switching elements 12. Reference numeral 16 denotes a differential amplifier, which calculates the difference between the outputs of the sample and hold circuits 14 and 15. 17 is a double pulse scanning circuit which outputs a double pulse to the switch element 12;

Next, the operation of the above conventional example will be explained.

First, the operation of this reading sensor is equivalent to that of an MO8 type IC sensor, and the scanning pulse for operating in charge accumulation mode enters the signal through the gate-drain capacitance of the switching element 12 and is superimposed, resulting in a low S/N ratio. becomes worse. In order to remove this noise, the switch element 12 connected to one light receiving element 11 is turned on and off twice, and the first output is sent to the sample and hold circuit 14.
．． The second output is held in the sample hold circuit 15,
A differential amplifier 16 takes the difference between the two and extracts only the signal component. FIG. 6 is an output waveform diagram of each element in FIG. 5, with waveforms (A), (B), (C)
, (D) are waveform diagrams of points a, b, 0, and d in FIG. 5, respectively. This first drive method will be explained in detail using this figure. First, the double pulse scanning circuit 1 sends the first pulse to the switch element 12 connected to the light receiving element 11.
Turn the feed on/off from 7. Then, the output at point a after passing through the integrator 13 becomes waveform (A) 21a. Well, when a sampling pulse is input to the sample and hold circuit 14 in synchronization with this, the output at point b is 22 of the waveform (B).
It becomes a. Next, when the second pulse is sent from the double pulse scanning circuit 17 to the same switching element 12 as the previous one and turned on/off, the output at point a becomes waveform 21b of waveform (A). Then, this time, a sampling signal is input to the sample hold circuit 15. The output at point 0 at this time is waveform (C) 23a. In these two consecutive pulses, the output waveform 21 at point a due to the first pulse
a is a superposition of an optical signal (shown with diagonal lines) and noise.

The output waveform 21b at point a due to the second pulse has no optical signal and is only noise. This is because the 1-reader unit operates in charge accumulation mode, so the same switch element 1
When pulses are continuously sent to 2, an optical signal is detected in the first pulse, but no optical signal is detected in the second pulse because there is no time to accumulate charge. On the other hand, noise is caused by the gate-drain capacitance of the switch element 12, and is generated each time the switch element 12 is turned on/off. Therefore, the output waveform (B) at point b and 0
When the output waveform (C) at point d is taken differentially using the differential amplifier 16, the output at point d becomes as shown in the output waveform (D), and the optical signal of the first light receiving element 11 is indicated by diagonal lines. 24a shown
is output as Similarly, the optical signal of the second light receiving element 11 becomes 24b. In other words, the first pulse of the double pulse reads out the optical signal noise, and the second pulse reads out the noise, and by taking this differential, the noise is canceled out.

(Problems to be Solved by the Invention) However, in the conventional image reading device, as described above,
A special double-pulse scanning circuit is required to send continuous 2 pulses (double pulses) to two switching elements, and two sample-hold circuits corresponding to the two pulses are also required. The method of driving the circuit also had the disadvantage of being complicated.

Therefore, the present invention has been made to solve these problems, and it is an object of the present invention to provide a small and thin image reading device that can obtain a large S/N ratio with a simple circuit configuration.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides an image reading device for reading an image to be read, which includes a plurality of light receiving elements, and one end of which is connected to the cathode of each of the light receiving elements. At the same time, a plurality of first switches whose other ends are all connected to a common line for bias, a plurality of second switches connected to form a pair with the first switches and whose one end is open, a shift register that sequentially disconnects a switch pair consisting of a first switch and a second switch; a first common line that connects the anodes of each of the light receiving elements in common; and a second common line that connects the other ends of each of the second switches in common. The second common line is connected to the first common line, and the second common line is connected to the second common line to obtain a differential output from the first common line and second common line. Preferably, the light receiving element is made of an amorphous semiconductor material whose main material is amorphous silicon.

(Function) According to the above configuration, the present invention functions as follows.

A differential amplifier calculates the difference between the first signal including the image signal and noise obtained via the light receiving element and the first switch, and the second signal containing only noise obtained via the second switch. Take. As a result, the noise component of the first signal is removed by the second signal (noise component only), and the first signal becomes only the image signal component. Therefore, the problems of the prior art described above can be solved. .

(Embodiment) FIG. 3 is a schematic diagram showing an embodiment of an image reading device according to the present invention. In the figure, 31 is a document that is an image to be read, 32 is a light source that illuminates the document 31, 33 is a converging lens array, and 40 is an image reading sensor. Here, the width of the light source 32 is the same as that of the original, and the LED chips arranged in a row are shown in FIG. 3, but other light sources include a fluorescent lamp, a tungsten lamp, a fluorescent display tube, Electroluminescence etc. may also be used. The light from this light source 32 illuminates the area of the document 31 to be read. Then, manuscript 3
The brightness and darkness of the light corresponding to the shading of 1 reaches the light receiving element 41 of the image reading sensor 40 via the converging lens array 33 that forms a royal life-size image. The original 31 can be read by converting the amount of light that has reached the light receiving element into an electrical signal.

FIG. 4 shows a sectional view of the light receiving portion of the image reading sensor.

It is shown upside down for explanation purposes. Here, 41 is a portion corresponding to the light receiving element shown in FIG. 3, and the material used here is amorphous silicon (a-3i), which has high photosensitivity and excellent stability of characteristics. 42 is glass,
A transparent substrate made of synthetic resin or any other suitable material. 43 is a transparent electrode constituting the first electrode deposited on this transparent substrate 42, and is made of indium tin oxide (I To
) Any other light-transmitting conductive material may be used. especially,
In the case of ITO, it is preferable to mix several percent of tin oxide with indium oxide and deposit it by electron beam or sputtering in an oxygen atmosphere. Moreover, the light receiving element 41 is a-8
In the case of i, tin oxide is often laminated on ITO to form a two-layer film. The light-receiving layer 44 a-8i has a three-layer structure, including a p layer and an i layer in order from the transparent electrode 43 side.

It is an n layer. This a-8i is produced by decomposing silane (SiH4) using high-frequency glow discharge.
It can be made at low temperatures. In this preparation process, for example, 500 to 10,000
ppm of diborane (B2H6) was mixed and the first layer, pea-8i layer, was laminated to a thickness of 50 to 1000X.
Next, a trace amount (looppm or less) of B2H6 is mixed with S i H, and a second layer of i-type a-
8i layer is laminated to a thickness of 0.5 to 1.5 μm, and further Si
500-110000 pp of phosphin/(
PH,) to form a third layer, n-type a-3, on the i-type layer.
The i-layer is laminated to a thickness of 100 to 2000A. After the three-layer a-8i is laminated on the transparent substrate 42 over the entire surface in this way, the a-8i is processed into the shape of the light-receiving layer 44. The shape of this light-receiving layer 44 is, for example, 8 dots in size.
In the case of a reading resolution of /-, 2048 dots are arranged in a straight line at approximately 100 μm square, and in the case of a reading width of 34 plates, for example. For this purpose, a resist pattern is created by ordinary photolithography, and unnecessary a-8i is removed by plasma dry etching. This etching is carried out under a reduced pressure of 10 to 100 Pa using a gas containing several to ten-odd percent of oxygen (0□) mixed with fluorocarbon (CF). Once the light receiving element 41 has been formed into the desired shape, an insulating layer 44 is formed thereon. This insulating layer only needs to be made of a high-resistance material such as silicon oxide, silicon nitride, or alumina, and methods such as sputtering have traditionally been used to create the film, which is the same method used for creating the a-8i. It is easier to use the glow discharge decomposition method, and the a-8i light receiving element 41
Because there is little sputter damage to the material, there is little variation in characteristics. To create the insulating layer 45 using this method, for example, in the case of silicon oxide, add nitrous oxide (N20) to SiH,
In the case of silicon nitride, ammonia (NHl) is added to SiH4.
) or/and nitrogen (N2) may be mixed. Finally, the electrode extraction portions on the light-receiving layer 44 and the transparent electrode 43 are removed, and a metal electrode 46 constituting the second electrode made of aluminum, nichrome, etc. is formed and completed. In this image reading sensor, the light indicated by the arrow is transmitted to the transparent substrate 42. Transparent electrode 43
It has a structure in which the light passes through and reaches the light receiving film 44.

FIG. 1 is a block diagram showing an embodiment of an image reading sensor of an image reading device according to the present invention. In the figure, reference symbol is a reading sensor head, inside which is the aforementioned light receiving element 4.
1, a signal switch 51, and a dummy switch 52. The function of shift register 53 is present.

Each signal switch and the dummy switch 52 are installed corresponding to one light receiving element 41, respectively.

One end of each signal switch 51 is connected to the cathode side of the corresponding light receiving element 41.

All other ends are connected together to a bias common line 61. Furthermore, each dummy switch 52.

One end thereof is left open without being connected to anything, and the other ends are all connected to the dummy common line 62. Further, the gate terminals of the signal switch 51 and the dummy switch 52 forming a pair are connected to the shift register 53 as a common gate terminal. On the other hand, the anode sides of the light receiving elements 41 are all connected together to a light receiving common line 63. Here, a positive voltage is applied to the bias common line 61 from the bias power supply 71 so that the light receiving element 41 is reverse biased. Further, outputs from the dummy common line 62 and the light receiving common line 63 are input to a differential amplifier 72.

The output of this differential amplifier 72 is outputted from an output terminal 73 as a read signal output.

FIG. 2 is a waveform diagram of the image reading sensor shown in FIG. 1, and the waveform (A) is the shift clock pulse 80. The waveform (B) is the light receiving pulse 81. on the light receiving common line 63. Waveform (C) is dummy common ff56
The dummy pulse 82 in FIG. 2, waveform (D) is the read signal pulse 83 output from the differential amplifier 72.

The operation of the image reading station shown in FIG. 1 will be explained with reference to FIG. 2. First, a shift clock pulse 80 of waveform (A) is input into the shift register 53. Then, with this first pulse 80a, a signal that turns on the signal switch 51a and the dummy switch 52a is output from the shift register 53, and the signal switch 51a and the dummy switch 52a are turned on.
a is turned on at the same time.

At this time, a light receiving pulse 81a having a waveform (B) in FIG. 6 is generated on the light receiving common line 63, and a tummy pulse 82a having a waveform (C) on the dummy common line 62. This received light pulse 81 is a superimposed optical signal and switch noise.

That is, the optical signal is a current that charges the accumulated charge that decreases according to the amount of light received by the light receiving element 41, and the switch noise is generated when the signal switch 51 is turned on and off, and is generated when the signal switch 51 is turned on and off.
This is noise caused by the capacitance between the drains. However, the dummy pulse 82 is only switch noise. That is, this is because the other end of the dummy switch 52 connected to the dummy common line 62 is open. In this way, the signal switch 51
Since the light reception pulse 81 due to 0 on/off is generated simultaneously on the light reception common line 63 and the dummy pulse 82 due to on/off of the dummy switch 52 is generated on the dummy common line 62, both pulses are input to the differential amplifier 72 and then If a differential is used, the switch noise component of the received light pulse 81a becomes the tammy pulse 82.
a, and the read signal pulse 83a output from the differential amplifier 72 becomes equivalent to the optical signal component of the received light pulse 81a.

As described above, according to this embodiment, the image reading device includes a light receiving element in the reading sensor head, a signal switch connected in series with this, a dummy switch paired with this, and a shifter that sequentially drives these. It has a register, and the read signal S/N ratio is obtained by taking the difference between the light reception pulse from the read sensor head and the dummy pulse. In addition, the other end of the signal switch was used as a common bias line, a positive voltage was applied so that the light receiving element was reverse biased, and the anode side of the light receiving element was connected to the differential amplifier as a common light receiving line, so the read sensor head could be used simply. It can be driven with one power source (for example, +5V). Therefore, a simple, small and thin reading device can be expected.

(Effects of the Invention) As described above, according to the present invention, a large S/N ratio can be obtained with a simple circuit configuration, and a small and thin image reading device can be provided.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram of the embodiment of Fig. 1, Fig. 3 is a schematic diagram of the embodiment of the invention, and Fig. 4 is a diagram of the embodiment of Fig. 3. 5 is a block diagram of a conventional image reading device, and FIG. 6 is a waveform diagram of FIG. 5.

Claims (2)

[Claims] (1) An image reading device that reads an image to be read includes a plurality of light receiving elements, and a plurality of first electrodes each having one end connected to the cathode of each of the light receiving elements, and all other ends connected to a common bias line. a plurality of second switches connected to form a pair with the first switch and having one end open; and a shift register that sequentially disconnects the switch pair consisting of the first switch and the second switch. , a first common line connecting the respective anodes of the light-receiving elements in common and a second common line connecting the other ends of the second switches in common to form the first common line and An image reading device comprising: a differential amplifier that takes a differential output from a second common line. (2) The image reading device according to claim 1, wherein the light receiving element is made of an amorphous semiconductor material whose main material is amorphous silicon.