JPS6097765A - Original reader - Google Patents

Abstract

PURPOSE:To obtain a reader where noise is eliminated sufficiently and a high S/N ratio is obtained by providing two signal lines and cancelling the noise produced from an MOS transistor (TR) with an identical MOS TR. CONSTITUTION:Plural MOS TRs 52a-52h connected to a shift register 50 and gates via control lines 51a-51h are connected to signal lines 53, 54 at an interval of one TR. The signal lines 53, 54 are connected to amplifiers 56, 57 and a signal with a low S/N ratio in which noise is mixed is obtained from the amplifiers. The signal is fed to changeover switches 58, 62 and a signal in mixture of an optical signal and the noise is extracted from the changeover switch 58 and a signal including the noise only is extracted from the changeover switch 62. In inputting the signals to a differential amplifier 61 for differential operation, an output signal with excellent S/N ratio without noise is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a novel noise reduction method in document reading devices such as facsimiles. More specifically, the conventional contact type image sensor, which enables the drastic miniaturization of document reading devices, has a condenser of the same size as the document, so it either comes in close contact with the document or uses an ozotic fiber. It is possible to read a document image by one-to-one combination using an optical system such as an array or a lens array. Since this method has a short imaging optical path length, it has a great advantage in that the document reading device can be significantly downsized compared to conventional MOS photodiode arrays or CCD image sensors.

Figure 1 (a) K conventional contact type image sensor etc. 1+
The circuit IIi is shown in the same figure (bl is an enlarged plan view showing the structure of the image sensor, and FIG.

Fig. 1 (in cl, the light receiving element is S e -A, 5-
Amorphous such as Te or a-8i:H, or &t CdS
, the top and bottom of the polycrystalline photoconductive semiconductor thin film 6 such as CdSe are
A divided electrode 2 made of a conductive thin film such as I, Au, or Cr;
nO,: It is made by sandwiching continuous conductive thin films such as ITO with an electric value of 4, and is represented by a 5 nsa CD, and has a density of 1 necessary to resolve the original, e.g. They are arranged in a line with 8 pieces per leg.

The charge accumulated in the capacitor CD according to the amount of light incident on the light receiving element 5 is discharged by the photodiode PD, and the MOS transistors 711,721..., 7n are sequentially connected to the capacitor by the shift register 6 at a certain interval. By recharging the CD and detecting the current at the ℃ output terminal 9 through the signal line 8, the light ↑I (can be read out).

In the above-mentioned contact type image sensor, it is preferable to form the light receiving element 5 on a single substrate 1 made of glass or ceramic by a method such as vapor deposition or a photo-etching process. ..., 7.
1 and the shift register 6 are individual elements! Therefore, f
Therefore, it is necessary to mount the scanning circuit 10 on the substrate 1 or another substrate and connect it to the light receiving element 5 using a connecting means 11 such as wire bonding.

In order to configure the contact type image sensor as described above,
It is necessary to route the wiring 12 drawn out from the light receiving element 5 so that it can be connected to the MOS transistors 1, 72+...7n. Therefore, the actual length of the leopard 112 is different from that shown in Fig. 1, and is quite long, and the signal line 8 is also several tens of centimeters long, which prevents noise coming in from the outside. The amount is ignored and it's tough. Furthermore, the spike-like noise that comes from the gate to the signal line 8 when turning on and off the MOS) Rungistaf 1 * 72..., 7n is also very harsh, and these noises cause the S of the contact type image sensor to
This causes the N ratio to decrease.

To solve the above drawback, two signal lines connected to the MOS transistors are provided, and a plurality of adjacent MOS transistors are alternately connected to the signal line, and one MOS transistor is switched continuously. Perform twice and differentially amplify the signal output from the above signal method2. A method has already been proposed for obtaining a signal with a good signal-to-noise ratio.

Fig. 2 shows a circuit diagram of the above system, and Fig. 3 shows its drive noll and output waveform. The operation of this system will be explained with reference to these drawings. In FIG. 2, 54. is used as a signal line.
35 is installed, MOS) Ranjistaro 2a ~ Ro 21
Several sources (three in this example) of the sources 41a to 41i are alternately connected to the signals 1>:sa and 6s. 40a1 to 40.1 shown in FIG. 6 by the shift register 66
signal lines 34, 35 by adding the /e signal of
The signal 34', 3 is a mixture of optical signal (shaded area) and noise.
5' is obtained, and by differentially amplifying both by the differential amplifier 68 of FIG. 2, the output terminal 6? In this case, only the optical signal shown in Fig. 3 is separated, and the output 39 has a good signal-to-noise ratio.
1 is obtained.

In this method, MOS) Ranjistaro 2a to 62 iV
It is very effective if the amount of noise generated from c is uniform for each transistor, but if there is a large variation in the noise generated, the noise cannot be completely eliminated, which causes problems when trying to achieve high sNvm. there were.

An object of the present invention is to eliminate the problems and shortcomings of conventional techniques in document reading devices such as facsimile machines, to sufficiently eliminate noise, and to obtain a high signal-to-noise ratio.
The purpose of this invention is to provide a standard noise reduction method.

Structure of the Invention The above object of the present invention is achieved by providing two signal lines and canceling noise caused by the MOS transistors by the same MOS transistor.

That is, the present invention distributes the output of a MOS transistor that reads the signal of a light receiving element by switching to a plurality of signal lines, and continuously switches the MQ transistor twice, and transfers the output obtained to the signal line to the MO8 transistor. )
This is achieved by a document reading device characterized in that the plurality of signals are separated into a plurality of signals by a changeover switch controlled by a transceiver, and then the plurality of signals are differentially excited and multiplied by 11], 7, and δ.

Example An embodiment of the present invention will be described with reference to the circuit diagram of FIG.

The circuit configuration of the document reading device 4 according to the present invention includes a control line 51
A plurality of MOS transistors 52a to 52h whose gates are connected to the shift register 50 through a to 51h have sources connected to signals $j15is, 54, 'J&C, and f. Note that in this embodiment f, eight light receiving elements 55 are used.
a to 55h are provided. After the two output signals generated on the signal lines 56 and 54 are incremented by 1 each by the intensifiers 56 and 57, one is passed through the selector switch 5B and the two sample and hold circuits 59 and 60. The other one is inputted to the differential amplifier 61 through the changeover switch 62, and the output of the differential amplifier 61 is connected to the switch 66 and output terminal. 68. The above changeover switch 58, 62 and switch 6
6 is controlled by inputs 65 and 67, and is turned on when the gates of the MOS transistors (1-1) constituting it are at the "High" level. The two sample and hold circuits 59 and 60 are controlled by inputs 64 and 65, and when the inputs are at the "High" level, they are in the sample state and when the inputs are at the "LO" level.
A hold state is assumed when the level is W''.

Next, the principle of operation of the circuit shown in FIG. 4 will be explained with reference to the timing chart shown in FIG. The shift register 50 operates by being supplied with manual data and a clock, and the control line sia~
Signal 51a at 51h? -511,1 occurs in all order I:Fi. Each of the signals 51a1 to 51hl consists of two consecutive pulses, each of which is one before and one after the other! U! Generate it so that it overlaps with the e-rus of the I control line. As a result, the output of the amplifiers 56 and 67 is a signal with a low S/N ratio that is a mixture of the optical 4r3 component (shown by the shaded area in the figure) and noise as shown in 56' and 57'. Next, by adding the a pulse signal 661 to the input 63 of the changeover switch 58.62, the output of the changeover switch 58.620 will be the im signal 581 which is a mixture of optical signal and noise, and the signal which is only noise. The output of the selector switch 58 is separated into sample and hold signals 621 by applying fixed pulse signals 64' and 65' to the inputs 64 and 65 of the sample and hold circuits 59 and 60, respectively. and the signals 69' and 60, respectively.
' as shown.

The output signal 60' of the sample-and-hold circuit 60 on the termination side obtained in this way and the sample-and-hold circuit 59
．． Output signal 62° of selector switch 62 without passing through 60
is input to the differential amplifier 61 and the differential -! -, a mixed signal 61' is obtained. When a ξ pulse signal 67' synchronized with the input 64 of the first sample and hold circuit 59 is applied to the input 67 of the switch 660, the output terminal 68, the miscellaneous) l- is removed and an output signal 681 with a very good C8N ratio is obtained.

Effects of the Invention As described above, according to the present invention, a signal with a good SN ratio can be obtained even if the amount of noise generated by a MOS transistor varies. Furthermore, two signal lines are provided, MOS transistors of adjacent light receiving elements are alternately connected to the iu@ line, and two consecutive switching operations are performed (signals 51a and 511+1 are composed of two t pulses). By doing these things in a mutually audible way,
Reading can be performed without wasting time to scan all elements.

Although it is possible to implement the same method as described above by using only one signal line, such a method would double the overall scanning time and would not be profitable.

As described in detail above, the present invention greatly contributes to reduction in noise, miniaturization, and improvement in performance of a document reading device.

[Brief explanation of drawings]

Figure 1 (a) + (b) and (C) are circuit diagrams and configuration diagrams of a conventional M-type image sensor, and Figure 2 is a circuit diagram of a conventional contact-type image sensor that has been improved to reduce noise. Figure 6 is a timing chart diagram of the conventional contact type image sensor shown in Figure 2, Figure 4 is a circuit diagram of the contact type image sensor according to the present invention, and a) Figure 5 is shown in Figure 4. FIG. 2 is a timing chart illustrating the Φb operation of the circuit of the present invention and a corresponding output signal waveform diagram. Reference numerals in the figure; 50...shift registers 51a to 511. ...1
[Flow line 52a to 52h...MOS) Transistor 5
3, 54...signal lines 55a-551. ... Light receiving elements 56, 57... Amplifiers 58, 62... Changeover switches 59, 60... Sample Hall 1 circuit 61... Differential amplifier 66... Switch 68...・Output terminal (3 others) Figure 1 (a)

Claims (1)

[Claims] In an original reading device in which a plurality of VC lower layer electrodes are provided on a substrate, and a photoconductor and a transparent conductive upper layer electrode are sequentially provided on the lower layer electrodes, the output of a MOS transistor that reads the signal of a light receiving element by switching is used. After dividing into a plurality of signal lines and continuously switching the MO8) synristor twice and separating the output obtained from the signal line into a plurality of single numbers by a changeover switch controlled by the MOS transistor, A document reading device characterized in that the plurality of signals are differentially amplified to produce an image signal.