JPS6232761A - Contact type image sensor - Google Patents

Abstract

PURPOSE:To obtain a high performance contact type image sensor without imposing the burden on a peripheral signal processing circuit by incorporating a sub-CCD drive circuit differentially erasing a DC offset level and a bias output for every CCD chip. CONSTITUTION:Each drive CCD chip 1 is constructed with the transfer stage of a 128-staged CCD shift register 2 and a 128-staged transfer gate 3. A charge arising in a photoelectric transducer element 5 is transferred to each corresponding CCD shift register 2 through the transfer gate 3. Its built-up charge is sequentially transferred and taken out as a time series signal. At this time, an auxiliary 128-staged CCD shift register 18 and a transfer gate 13, both of which have the same arrangement and construction, are installed on the same chip 1, and a charge is outputted to a suboutput line 17 in the same timing as that of a signal charge. This output value is roughly the same as the output value of a main output line 12 at dark, and the outputs of the main- and sub- output lines 12 and 17 are inputted to an external differential amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a contact image sensor used as a photoelectric conversion device in facsimiles, optical character recognition, copying machines, and the like.

(Prior art and its problems) Compared to MO8 type IC image sensors, CCD image sensors, etc., contact type image sensors do not use a reduction optical system using lenses, so facsimile machines etc. can be made smaller and more economical. Are better.

As a photoelectric conversion element material for this contact type image sensor, amorphous silicon (hereinafter referred to as a-8i), which has high photosensitivity in the visible light region and can be easily formed in a large area, has recently been frequently used.

This a-8i has a high specific resistance and is suitable for W, load accumulation mode operation like a CCD image sensor or a MOS image sensor. In this case5, the element structure is usually a structure in which a-8i is sandwiched between upper and lower IKs, but by adopting such a sandwich structure, the optical response speed of the element is also 0.1 m5ec or less. This high speed can be achieved.

An image sensor suitable for high-speed reading devices can be obtained.

A drive circuit that can read the optical signal charges generated by this A-8i photoelectric conversion element at high speed, efficiency, and high sensitivity is shown in Japanese Patent Application No. 59-143020, ``Fixed type image sensor and its driving method.'' There is a CCD drive circuit. The structure of a contact type image sensor using this circuit is shown in FIG. To briefly explain this diagram, CC
D shift register 21° transfer gate row 22.
and an input terminal row 24 of the driving CCD 20 which includes at least a floating gate amplifier 23 and an A-8T photoelectric conversion element 2 formed on a glass substrate 26, for example.
Five individual electrode terminal examples 27 are connected in a one-to-one correspondence with bonding wires 28.

After the optical signal charge generated by the a-8t photoelectric conversion element 25 is sent to the CCD shift register 21 through the transfer gate 22, the transfer clock φ1. Transferred sequentially in chronological order by φ2,
It will be released through.

This driving CCD chip 2o is usually composed of 64 bits/1,000 chips or 128 bits/chip, considering its yield and the like.

The contact type image sensor is A4 size or 84 size, etc., and consists of a large number of elements of several thousand bits or more. Therefore, the configuration example shown in FIG.
This is an example of only one item, but in reality, several items are lined up. for example,
If a 128-bit/chip CCDJk moving block is used to operate an A4-size, 8-fold, close-contact type image sensor, 14 chips are required. These 14 chips are usually mounted in a hybrid manner on the same glass substrate, similar to the example shown in Figure 3.In addition, the clock terminals and output terminals of each chip necessary for driving are input/output. The terminal row 29 is designed in accordance with Japanese Patent Application No. 59-164445R from the viewpoint of reliability and to simplify external connections.
They are commonly connected as shown in "Contact Image Sensor and Its Driving Method".

However, these driving CCD chips 2o.

When randomly selected and mounted, the DC offset level usually varies by about 1 V due to variations in characteristics of floating gate amplifiers between chips. By the way, in a normal CCD design, the bright output is set to about 1V.

Therefore, as shown in Figure 4, the output waveform of the entire contact type image sensor becomes a waveform with steps due to the difference in DC offset between chips, making it difficult to perform signal processing such as binarization or halftone reading. do not have.

It is possible to process waveforms using memory, taking DC offset into account, but the waveforms vary depending on each device, and extra circuits such as memory are required, so it is difficult to reduce size and cost. become unattainable.

Furthermore, in such a hybrid CCD drive type, the element capacitance becomes large, so that afterimages occur, which becomes a problem. As a method for effectively suppressing this afterimage, a method of injecting a bias charge was previously proposed as shown in Japanese Patent Application No. 164445/1983 [Contact image sensor and its driving method]. In this method, a type of DC offset is formed because a bias charge is also mixed into the signal output side. For example, this amount of charge may also be comparable to bright output. Even if a fixed amount of charge is injected, considering the variation in the gain of the floating gate amplifier between chips, the signal output will vary by about 0.3 V for a signal output of about 1 V, for example.

As mentioned above, in the hybrid CCD drive type, variations in the DC offset and variations in the bias output corresponding to the bias charge occur in the output signal, and it may not be possible to use it as is, or it may cause a large amount of damage, such as causing extremely complicated damage to one peripheral circuit. There was a problem.

(Object of the Invention) The object of the present invention is to eliminate such drawbacks and to provide a high-performance contact type image sensor using an A-8I photoelectric conversion element and a CCD drive IC without placing a burden on the peripheral signal processing circuit. It is about providing.

(Embedding of the Invention) According to the present invention, one or more photoelectric conversion element arrays each including at least a plurality of photoelectric conversion element arrays, a transfer gate, a CCD shift register, an output amplifier, a switching circuit, and an input mechanism for injecting charge. A contact image sensor comprising at least a driving integrated circuit on an insulating substrate, wherein the driving integrated circuit includes a plurality of stages of transfer gates and a plurality of stages of CCD shift registers connected to the mA stage transfer gate. At least an output amplifier connected to the plurality of stages of CCD shift registers, a switching circuit provided after the output amplifier, and an input mechanism for electrically injecting charge into the first stage of the plurality of stages of CCD shift registers. main and sub-CCD drive circuits configured,
The inputs of the plurality of stages of transfer gates of the D drive circuit are connected to the plurality of photoelectric conversion element arrays, and the outputs from the switching circuits of the main and sub CCD drive circuits are connected to the insulating substrate, respectively. It is characterized in that it comprises at least main and sub-output lines to be taken out.

(Operation of the invention, original U) In the present invention, in a close-contact image sensor using one or more driving CCDs, particularly practically M several, 11*, offset levels and bias outputs are differentially canceled. Secondary CCDt'? Each CCD tinopub σ has a built-in circuit.

In the above configuration, since it can be built in the same chip and close to each other, there is almost no variation between the main CCD drive circuit and the sub CCD drive circuit, and the dark current generated in the offset, bias output, and CCD shift register is eliminated. There is no difference in the values of noise, etc.

Therefore, by making these differentials, variations between the 1,000 knobs are eliminated, and the output waveform of the entire contact type image sensor is a pure bright output as an absolute value from the ground without offset.

Furthermore, the IF+f output can also be hydraulically suppressed, making it possible to achieve a high-performance ¥M electrodeposition type image sensor that is no different from a CCDIC image sensor.

(Example) Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows the structure of a contact type image sensor according to an embodiment of the invention. Each driving CCD chip 1 is 1
For example, it is composed of transfer stages of a 128-stage CCD shift register 2. These 128 stages of CCDs are connected in series.
The shift register 2 is composed of, for example, a transfer efficiency channel CC1 shift register (hereinafter simply referred to as a CCD shift register). Transfer gates 3 of 1 to 11 or more stages are connected to each stage, and on the input side thereof, 1, for example, a 2t a-8 is mounted on a glass substrate 4.
The i-photoelectric transformation elements 5 are connected one-to-one by bonding wires 6. This a-8i nine-way change element 5 is,
Individual electrodes 7 made of Au etc. and Indium Tin 0xi
It is composed of an A-8T thin film sandwiched between transparent common electrodes 8 made of DE (hereinafter referred to as ITO) or the like.

The signal charges generated in this a-8i photoelectric conversion element 5 are as follows.

The signals are transferred to the corresponding CCD shift registers 2 through the transfer gates 3. after that.

For example, if the transfer clock is a 2-phase clock,
Charge No. 411 accumulated in each clock cycle is sequentially transferred to the primary stage and taken out as a time-series signal.

At this time, bias charges to enhance the afterimage suppression effect are injected in advance from the bias charge input section 9 into the CCD shift register 2, and from the CCI) shift register 2 to the a-8L optical conversion element 5 side, and are injected together with the signal charges. Move it into the CCD shift register 2 again.

The time series signal output from the CCD shift register 2 is
A voltage output from the 70-ting gate amplifier 10 is output to the main power source 812 through the output changeover switch 11. At this time, on the same chip 1, there are sub-128-stage CCD shift registers 18 and 12 with the same arrangement and configuration.
8-stage transfer gate 13, bias charge input section 14° floating gate amplifier 15, switch 16
It has a function and is outputted to the sub-output line 17 at the same timing as the signal charge as described above. This output value is the same as the output value of the main output line 12 when it is dark.

For example, in the case of an A4-sized, 8-element/Totoku-type image sensor, in which 128 stages/chip, 6 drive CCDs 1 each have 5, 128 stages/chip, 14 CCDs are mounted on the glass substrate 4, and one is not shown in the figure. , a transfer clock, a transfer gate, a gate terminal for an output changeover switch, etc., and the main output line 12.
, the sub-output line 17, and other common terminals are connected to each other. The respective signal outputs from the main output line 12 and the sub output line 17 are input to an external differential amplifier.

2(a), (b) and (e), the main output edge 12.
An example of the output waveform after differential of the sub output line 17 and these two output lines is shown. As mentioned above, the output waveform appearing on the main output +M121 is composed of DC offset, reset noise 0 due to reset pulse, bias output, bright signal output, etc. 1, and g1j output line 17 has DC offset, reset noise, and bias. Output etc. appears. These waveforms vary among each chip as seen in Figure 2, but the main and the same amount on the same chip are normal LSI
Like chips, there is almost no fluctuation. Therefore, the final output waveform is output as an absolute value from the ground level, which provides only a pure bright signal output and is very convenient for subsequent signal processing.

It should be noted that although the dark current component generated within the A-8T photoelectric conversion element cannot be canceled, this value does not pose a problem since it is small, about 1/1000 S lower than the bright signal output during normal use. Also, considering the dark current generated by the CCUCC shift register and the transfer efficiency, it is better to provide the same number of differential CCD shift registers and transfer gates as in the present invention, but this also applies to DC offset and floating gate amplifiers. This is much smaller than the variation in , and does not pose a problem like the dark ME flow component in the previous element. Therefore, if there are restrictions on the arrangement, configuration, etc. on the chip, the number of differential stages may be one, and the effect will be almost the same.

(Effects of the Invention) As detailed above, according to the present invention, variations in DC offset between chips, floating gate amplifiers, etc., which were problems in the A-8T contact type image sensor using multiple CCD drive circuits. The noise generated by the I
By providing a sub-circuit on each chip that can be easily configured with the same design and process as the drive circuit, it is possible to effectively suppress noise and achieve a noise reduction that is equal to or even lower than that of the original CCD IC image sensor. There is an effect. Therefore, it has become possible to apply it to devices such as high-speed, high-performance facsimile, OCR, and copying machines that conventionally used CCDIC image sensors, and has achieved a close-contact image sensor that can greatly contribute to the miniaturization of such devices. It has the advantage of being possible.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an embodiment of the present invention, Fig. 2 is an output waveform diagram showing the operation of the present invention, Fig. 3 is a perspective view showing a conventional example, and Fig. 4 is a conventional output waveform. FIG. 1.20...Drive CCD chip, 2.21...CCD shift register, 3.22...
Transfer gate, 4.26...Glass substrate, 5
, 25... Photoelectric conversion element, 6.28... Bonding wire, 7.27... Individual electrode, 8... Common electrode, 9... Bias charge input section, 10.23... 70- tinggate amplifier. DESCRIPTION OF SYMBOLS 11... Output switching switch, 12... Main output edge, 13... Sub transfer='7'-to 14... Sub bias charge input section, 15... Sub floating gate amplifier, 16...・・・
Sub-output selector switch, 17... Sub-output line, 18... Member IJ CCD shift register 24... Input terminal, 29... Input/output terminal.

Claims (1)

[Claims] One or more driving integrated circuits each including at least a plurality of photoelectric conversion element arrays, a transfer gate, a CCD shift register, an output amplifier, a switching circuit, and an input mechanism for injecting charge. In a contact image sensor provided at least on an insulating substrate, the driving integrated circuit includes a plurality of transfer gates, a plurality of CCD shift registers connected to the plurality of transfer gates, and a plurality of CCD shift registers connected to the plurality of transfer gates. A main circuit comprising at least an output amplifier connected to a CCD shift register, a switching circuit provided after the output amplifier, and an input mechanism for electrically injecting charge into the first stage of the plurality of stages of CCD shift registers. A sub CCD drive circuit is provided, the inputs of the plurality of stages of transfer gates of the main CCD drive circuit are connected to the plurality of photoelectric conversion element arrays, and further the main and sub CCDs are arranged on the insulating substrate. A contact type image sensor comprising at least main and sub output lines for respectively taking out outputs from the switching circuit of a drive circuit.