JPS61184964A - Picture reader - Google Patents

Abstract

PURPOSE:To obtain a large S/N and to attain high-speed operation by providing a signal switch connected in series with a photodetector to a drive section of a picture read sensor and a dummy switch in pairs therewith and applying differential operation to both outputs. CONSTITUTION:When the 1st pulse of a shift clock enters a shift register 4, a pulse turning on a signal switch 2 and a dummy switch 3 is outputted from the shift register 4. Since the output pulse of the signal switch 2 is generated in a signal common line 5 and an output pulse from the dummy switch 3 is generated in a dummy common line 6 at the same time, both pulses are processed differentially by using a differential amplifier 7, then the switching noise of rejection mode is cancelled and an optical signal pulse is obtained at an output terminal 8.

Description

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

(Prior Art) Generally, a contact type image reading device has light receiving elements arranged in a straight line at intervals equal to the reading resolution. This light-receiving element has the same width as the image to be read, and is configured to read the image through a converging lens that forms an erect, equal-sized image.

As such a device, Proceedings of the Institute of Image Electronics Engineers 83-04-
1 (high-speed amorphous silicon contact type image sensor).

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, for example, 7 amorphous silicon, which has excellent photoelectric conversion characteristics, manufacturability, and stability, and also provides a high optical response speed when operated in a charge accumulation mode with high resistance. (hereinafter abbreviated as a-3i). 12 is a switch element, for example M
It is composed of O3 type FET. 13 is an integrator that converts the sawtooth waveform generated from the switch element 12 into a square wave. 14 and 15 are sample and hold circuits that output pulse signals corresponding to two consecutive pulses (double pulses) to each of the switch elements 12; 1G is a differential amplifier, which takes the difference between each output from the sample and hold circuits 14 and 15. A double pulse scanning circuit 17 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 MO3 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. In order to remove this noise, the switching 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,
Differential amplifier 16 takes the difference between the two and extracts only the signal component. FIG. 2 is an output waveform diagram of each element in FIG. 1, and waveforms (A), (B), (C), and (D) are points a, b, C, and d in FIG. 1, respectively. It is a waveform diagram of points. This drive system will be explained in detail using this figure. First, 1 is connected to the switch element 12 which is connected to the light receiving element 11.
The second pulse is sent from the double pulse scanning circuit 17 and turned on/off. Then, the output at point a after passing through the integrator 13 becomes waveform (A) 21a. Therefore, when a sampling pulse is input to the sample hold circuit 14 in synchronization with this, the output at point b becomes waveform 22a of waveform (B). Turn feed on/off. Then,
The output at point a becomes waveform (A) 21b. This time, a sampling pulse is input to the sample hold circuit 15. The output at point C at this time is 23a of waveform (C)
becomes. In these two consecutive pulses, the output waveform 21a at point a due to the first pulse is a superposition of the optical signal (shown with diagonal lines) and noise, and the output waveform 21a at point a due to the second pulse 21b has no optical signal, only noise. This is because the single-read sensor operates in charge accumulation mode, so when pulses are sent to the same switching element 12 in succession, an optical signal is detected in the first pulse, but a charge is detected in the second pulse. The optical signal is not detected because there is no time to accumulate the noise, while the noise
This is caused by the gate-drain capacitance of No. 2, and occurs every time the switch element 12 is turned on/off. Therefore, if the output waveform at point b (B) and the output waveform at point C (C) are differentiated using differential amplifier 1B, the output at point d will be as shown in the output waveform (D). , the optical signal of the first light-receiving element 11 is output as a shaded 24a. 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 molecular 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,
Two consecutive pulses to one switch element (double pulse)
A special double-pulse scanning circuit is required to send out the pulses, and two sample-hold circuits corresponding to the two pulses are also required. Furthermore, the method of driving these circuits is also complicated.

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

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides an image reading device that reads an image to be read, in which a plurality of light-receiving elements are arranged at equal intervals and have the same width as the image to be read. and a first switch connected in series to each of the light receiving elements, and a first switch connected in series to each of the light receiving elements.
a second switch coupled to form a pair with the switch and having one end open; a shift register that sequentially disconnects the switch pair consisting of the first and second switches; and each of the first switches. A first common line and a second common line whose other ends are commonly connected.
A differential amplifier is provided, which connects the other ends of each of the switches to a second common line which is commonly connected, and obtains a differential output of each common line.

(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 it. 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.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a light-receiving element, which is composed of a-3T, etc., and a reverse bias voltage V is applied to all of the light-receiving elements 1. 2 is a signal switch, 3 is a dummy switch,
Each of them is composed of, for example, an MO3 type FET. The signal switch 2 and the dummy switch 3 have respective gate terminals in common and are connected in series. 4 is a shift register, signal switch 2
A pulse is output to turn on each of the dummy switches 3 and 3. A signal common line 5 connects the gates or drains of a plurality of signal switches 2 in common. A dummy common line 6 connects the gates or drains of a plurality of dummy switches 3 in common. 7 is a differential amplifier, and signal switch 2
and each output from the dummy switch 3. 8 is an output terminal from which the output of the differential amplifier 7 is obtained.

Next, the operation of this embodiment will be explained.

First, to briefly explain, in this embodiment, the pulses from the shift register 4 are transferred to the signal switch 2 and the dummy switch 3.
The output pulses are simultaneously input to the gate terminals of the two signals, and the respective output pulses are differentiated by a differential amplifier 7 to extract only the signal components. 2 is an output waveform diagram of the image reading sensor in FIG. 1, in which waveform (A) is the shift clock pulse input to the shift register 4, waveform (B) is the pulse on the signal common line 5, and waveform (C) is the Pulse on dummy common line 6,
Waveform (D) is a pulse at the output terminal 8 of the differential amplifier 7. The operation of this embodiment will be explained in detail using this figure. First, when the first pulse of the shift clock of waveform (A) enters the shift register 4, a pulse that turns on the signal switch 2 and the dummy switch 3 is output from the shift register 4. First, consider when the signal switch 2 is turned on. The output at this time is an optical signal corresponding to the amount of light received by the light receiving element 1 and switching noise caused by the gate-drain capacitance of the signal switch 2, and becomes a pulse as shown in waveform (B). On the other hand, the dummy switch 3 is not connected to the light receiving element 1, and one terminal thereof is open. Therefore, when the dummy switch 3 is turned on, the output becomes a pulse as shown in waveform (C) with only the above-mentioned switching noise. In this way, the output pulse of the signal switch 2 is generated simultaneously on the signal common line 5, and the output pulse of the dummy switch 3 is generated on the dummy common line 6, so if these two pulses are differentiated using the differential amplifier 7, switching noise will be generated. The waveform (
An optical signal pulse as shown in b) is obtained. Here, it is necessary to select the signal switch 2 and the dummy switch 3 that have the same characteristics, but if they are integrated into an IC and housed in the same chip, the same characteristics can be obtained.

FIG. 3 is a schematic diagram showing an apparatus using the image reading sensor of this embodiment. 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 one in which LED chips are arranged in a row is shown in FIG. The light from this light source 32 illuminates the part of the document 31 to be read. Then, the brightness and darkness of the light corresponding to the density of the original document 31 reaches the light receiving element 41 of the image reading sensor 40 via the converging lens array 33 which forms an image of the original text at the same size. 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 is a sectional view showing the light receiving section of the image reading sensor of this embodiment. In the figure, reference numeral 41 denotes 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 a transparent substrate made of glass, synthetic resin, or any other suitable material. Reference numeral 43 denotes a transparent electrode constituting the first electrode deposited on the transparent substrate 42, and any light-transmissive conductive material such as indium cast oxide (ITO) may be used. In particular, when ITO is used, indium Mix a few percent of tin oxide with the oxide,
It is preferable to evaporate by electron beam or sputtering in an oxygen atmosphere. Also, when the light receiving element 41 is a-3i, I
Tin oxide is often layered on top of TO to form a two-layer film.
A-3i of the light-receiving layer 44 has a three-layer structure, and the transparent electrode 43
In order from the side, they are a p layer, an i layer, and a ne layer. This a-3i can be produced at a low temperature of 200 to 300°C by decomposing silane (S, H,) with high frequency glow discharge. In this production process, for example, SiH is mixed with 500 to 100 OOPP of diporan (B2H6) and the first p-type layer-Si layer is laminated to a thickness of 50 to 1000 mm, and then SiH4 A trace amount (1100
Mix B and H6 (pp or less) and form a second i-type layer-3i layer on top of the P-type layer at a thickness of 0.5 to 1.5 ILm (1)
Laminate to thickness. Furthermore, 500 to 1o0 for Si horses
00pp of phosphine (PH3) is mixed and a third n-type layer-5i layer is laminated on the i-type layer to a thickness of 100 to 2000λ. In this way, a-
3i is laminated on the transparent substrate 42, this a-5i
is processed into the shape of light receiving M44. The shape of the light-receiving layer 44 is, for example, about too IL-angle when the reading resolution is 8 dat/m. In other words, in the case of the reading width of 84 editions, 2048 dats are arranged in a straight line. For this purpose, a resist pattern is created by ordinary photolithography, and unnecessary a-3i is removed by plasma dry etching. For this etching, add several oxygen (02) to Freon (CF4)! It is carried out under a reduced pressure of 10 to 100 Pa using a mixed gas of several percentages of θ.

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 as the a-5i. It is easier to use the glow discharge decomposition method, and the a-5i light receiving element 4
Since there is little sputter damage to 1, there is little variation in characteristics.

To create the insulating layer 45 using this method, for example, in the case of silicon oxide, nitrous oxide (N20) is added to SiH,
In the case of silicon nitrogen, S, H, ammonia (NH3
) 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. This image reading sensor has a structure in which light indicated by an arrow passes through a transparent substrate 42 and a transparent electrode 43 and reaches a light receiving layer 44 .

(Effects of the Invention) As explained above, according to the present invention, the driving section of one image reading sensor has a signal switch connected in series with the light receiving element and a dummy switch paired with the signal switch, and the output of both is provided. By obtaining only the optical signal by using differential,
It is easy to integrate the circuit, and even though the amplifier circuit is simple, it can be expected to have a large S/N ratio and high-speed operation.
It can be applied to an L-type image reading device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing the output waveform of each element in the image reading sensor of FIG. 1, and FIG. 3 is a diagram showing the output waveform of each element in the image reading sensor of this embodiment. 4 is a cross-sectional view showing the light receiving section of the image reading sensor of this embodiment, FIG. 5 is a block diagram showing the configuration of a conventional image reading device, and FIG. 6 shows each of the components shown in FIG. 5. FIG. 3 is a diagram showing an output waveform of an element. 1.11.41-m-light receiving element, 2-m-signal switch, 3-m-dummy switch, 4-m-shift register, 5-m-signal common line, 6--
-Dummy common line, 7.18-m-differential amplifier, 8--one output terminal, 12-m-switch element, 13-m-integrator, 14.15-m-sample hold circuit 17--double pulse scanning circuit, 31--one original, 32-m-light source, 33--one focusing lens array, 40-m=image reading sensor, 42-m-transparent substrate, 43-m-transparent electrode. 44-m-light receiving layer, 45-m-insulating layer, 46--metal electrode. Patent Application Hitoki Electric Industry Co., Ltd. Patent Application Agent

Claims (1)

[Claims] An image reading device that reads an image to be read includes: a plurality of light receiving elements disposed at equal intervals with the same width as the image to be read; a first switch having one end connected to each of the light receiving elements; a second switch coupled to form a pair with the switch and having one end open; a shift register that sequentially connects and disconnects the switch pair consisting of the first and second switches; and a shift register for each of the first switches. The first with the other end connected in common
a common line and a second common line to which the other ends of each of the second switches are connected in common, and a differential amplifier that takes a differential output of each common line, the light-receiving element and the 1st
A first signal including an image signal and noise obtained via the switch and a second signal containing only the noise obtained via the second switch are differentially obtained via the differential amplifier. An image reading device characterized in that only the image signal is extracted by canceling out the noise.