JPH0897965A - Close contact type image sensor - Google Patents

Abstract

PURPOSE: To obtain the image signal output with excellent S/N by uniformizing and reducing noise charge stored in each read capacitor in the close contact image sensor provided with plural read capacitors. CONSTITUTION: Read capacitors CT1 -CT48 are reset by simultaneously closing switches K1 -K48 in a timing just before a time when signal charges are transferred to the read capacitors CT1 -CT48 . Since the length of the period after the read capacitors CT1 -CT48 are reset till the succeeding signal charges are stored is identical and short, the noise charges stored in each read capacitor is uniformed and decreased and then an image signal output with excellent S/N is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact type image sensor used in a facsimile, an image scanner, etc., and more particularly, an array-shaped photoelectric conversion element is divided into a plurality of blocks, and the photoelectric conversion elements are divided into blocks. The present invention relates to a contact-type image sensor having a matrix signal wiring configuration, which is configured to convert a parallel image signal from the above into a serial image signal and output the serial image signal.

[0002]

2. Description of the Related Art Recently, a contact type image sensor having an equal-magnification optical system has been used for downsizing of facsimiles, image scanners and the like. There are many types of contact type image sensors due to differences in photoelectric conversion elements, scanning methods, etc., but matrix type contact type image sensors using thin film transistors (hereinafter referred to as TFTs) as scanning switching elements are also often used. . An example of such a contact image sensor is disclosed in Japanese Patent Laid-Open No. 3-231.
It is disclosed in Japanese Patent Publication No. 560.

FIG. 5 is an equivalent circuit diagram of the contact image sensor described in the above publication. FIG. 6 is a timing chart showing the operation. Referring to FIGS. 5 and 6, the optical image of the read original is photoelectric conversion elements S _{1-1 to} S 1.
_It is incident on _36-48 and converted into photocurrent, and signal charges are stored in storage capacitors C _{1-1 to} C _36-48 . The signal charges stored in the storage capacitors C _{1-1 to} C _1-48 of the first block are transferred from the shift register SR ₁ through the gate line G ₁ to the gate pulse P _G1 by the transfer TFT T _1-1.
In the period t ₁ the through T _1-48 is turned on is transferred to the earth capacitance C _L1 -C _L48 of matrix signal wire L ₁ ~L _48.
Then, the signal charge of the first block is the period t ₃ when the switches U _{1 to} U _{48 to} which the control pulse P _U is applied are in the ON state.
To the read capacitors C _{T1 to} C _T48 . Further, the switch T ₁ through T ₄₈ the control pulse P ₁ to P ₄₈ from the shift register SR2 is applied is sequentially turned on,
The signal charge of the first block, which has been transferred to the read capacitors C _{T1 to} C _T48 , is output through the amplifier AMP as an image signal output V.
It is output as ₀ during the period t ₄ .

The storage capacitors C _{1-1 to} C _1-48 are reset TFTs R _{1-1 to} R _1-48 to which a gate pulse P _G2 is applied from the shift register SR1 through the gate line G _2.
Is reset by the DC power supply V _R during a period t ₇ in which is turned on. The ground capacitances C _{L1 to} C _L48 of the matrix signal wirings L _{1 to} L ₄₈ are C for signal charge reading.
After being transferred to the _T1 -C _T48, the control pulse P switch R ₁ to R _{48 in which R} is applied to the period t ₂ to be turned on, and is reset by the DC power supply V _R. Next, the reading capacitors C _{T1 to} C _T48 are sequentially reset by the DC power supply V _R during a period in which any of the switches T _{1 to} T _{48 and} the switch V to which the control pulse P _V is applied are simultaneously turned on. . For example, the reading capacitor C _T1 is reset during the period t _{5 in} which the switch T ₁ and the switch V are simultaneously turned on. The reading capacitor C _T48 is reset during a period t _{5 in} which the switch T ₄₈ and the switch V are in the ON state at the same time. The reading capacitor C _T48 is reset during the period t _{8 in} which the switch T ₄₈ and the switch V are simultaneously turned on.

Thereafter, the transfer and accumulation of signal charges and the resetting of the reading capacitor are sequentially performed in block units.
An image signal output V ₀ corresponding to the optical image of the read original incident on the photoelectric conversion elements S _{1-1 to} S _36-48 is output from the amplifier AMP.

[0006]

In this conventional contact type image sensor, the timing at which the signal charges are transferred to the read capacitors C _{T1 to} C _T48 is the read capacitor C _T1 to C _T1 .
It is the same (t ₃ or t ₉ ) for all of C _T48 , while the timing at which the reading capacitors C _{T1 to} C _T48 are reset is different for all of the capacitors C _{T1 to} C _T48 ( t like ₅ or t ₈₎ Therefore, both the length of time since the resetting until the signal charges are transferred differently. For example, while the read capacitor C _T1 has a length of the period t ₁₀ , the read capacitor C _T1 has a length of t _{10.
At T48} , there is only the length of the period t ₁₁ .

If the period from the reset to the transfer of the signal charges is long, the read capacitors C _{T1 to} C _T48 are not _affected by the signal charges due to leakage of the switches U _{1 to} U ₄₈ and the switches T _{1 to} T _48. A problem arises that the noise charge of is accumulated. In the conventional contact-type image sensor, the amount of this noise charge is the largest in C _T1 and the smallest in C _T48 , and accordingly, there is a problem that the image signal output V ₀ increases / decreases in the block cycle.

[0008]

According to the contact type image sensor of the present invention, each of a plurality of photoelectric conversion elements arranged in an array forms a plurality of signal charges generated in response to incident light from the outside. After the conversion element is divided into a plurality of blocks, a parallel image signal for each block is collectively transferred to the readout capacitors individually provided on the matrix signal wirings connected to the photoelectric conversion elements, and then transferred to the respective readout capacitors. In a contact image sensor having a matrix signal wiring structure configured to sequentially perform the operation of converting the parallel image signal into a serial image signal and outputting the serial image signal by sequentially reading the transferred parallel image signal, Immediately before the batch transfer of the parallel image signals to the reading capacitors, all the reading capacitors are batched at the same time. Characterized in that a means for resetting the same voltage.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an equivalent circuit of the first embodiment of the present invention. Further, FIG. 2 is a timing chart showing the operation. With reference to FIGS. 1 and 2, in the present embodiment, the optical image of the read document incident on the photoelectric conversion elements S _{1-1 to} S _36-48 such as a photoconductor and a photodiode is converted into a photocurrent. Storage capacitor C _1-1 ~ C
_36-48 , transfer TFTs T _{1-1 to} T _36-48 , gate wirings G _{1 to} G ₃₇ , matrix signal wirings L _{1 to} L ₄₈ and their ground capacitances _{CL 1} to _{CL 48} , shift register SR 1, switch U
_{1 to} U ₄₈ , reading capacitors C _{T1 to} C _T48 , switch T
_{1 to} T ₄₈ , the shift register SR2 and the amplifier AMP are used to output the image signal output V ₀ . The operation up to this point is the same as that of the conventional contact image sensor shown in FIGS. In addition, the reset TFT R _1-1
To R _36-48, the shift register SR1 and the DC power source V _R
Reset operation and the switch R ₁ to R ₄₈ of the storage capacitor C _1-1 -C _36-48 by, the earth capacitance C _L1 -C _L48 of Matorisuku signal lines L ₁ ~L ₄₈ by the DC power source V _R reset operation also of conventional It is the same as the contact image sensor.

This embodiment differs from the conventional contact image sensor in terms of an equivalent circuit in that a reading capacitor C _{T1 is used.}
~ To reset C _T48 , conventionally, switches T ₁ ~ T
Whereas ₄₈ and switch V were used, switch K
_{1 to} K ₄₈ is used. The difference of this embodiment from the conventional one in terms of operation timing is that the reading capacitor C _T1
~ The timing of resetting C _T48 is conventionally C _T1 ~ C
_Although different for all of _T48 , the present embodiment is the same for all of C _{T1 to} C _T48 , and is a point immediately before the next signal charge is transferred.

The signal charge of the first block is the control pulse P.
In the period t ₃ when the switch U ₁ ~U _{48 which U} is applied is turned on, the earth capacitance C of the matrix signal wirings L ₁ ~L _48
The data is transferred from _{L1 to} C _L48 to the read capacitors C _{T1 to} C _T48 . In the period t ₁₂ immediately before this period t ₃ , the control pulse P
Switches K _{1 to} K ₄₈ to which _K is applied are turned on,
The reading capacitors C _{T1 to} C _T48 are simultaneously reset by the DC power supply V _R. Similarly, the read capacitors C _{T1 to} C _T48 are simultaneously reset in the period t ₁₃ immediately before the period t ₉ in which the signal charges of the second block are transferred. The lengths of the period t ₁₄ and the period t ₁₅ from the resetting of the read capacitors C _{T1 to} C _T48 to the transfer of the next signal charge are extremely small and set to 1/100 or less of the length of the period t _1. To be done.

Next, FIG. 3 is an equivalent circuit diagram of the second embodiment of the present invention. FIG. 4 is a timing chart showing the operation. With reference to FIGS. 3 and 4, in the present embodiment, the optical image of the read original incident on the photoelectric conversion elements S _{1-1 to} S _36-48 such as a photoconductor and a photodiode is converted into a photocurrent, The operation until output as the image signal output V ₀ is the same as that of the first embodiment shown in FIGS. 1 and 2. Further, the DC power source V _R and the switch K ₁ ~K ₄₈
And the read capacitors C _{T1 to} C _T48 at the same time,
Moreover, the operation of resetting immediately before the signal charge of the next block is transferred is the same as in the first embodiment. The second embodiment differs from the first embodiment in that a storage capacitor C
_1-1 ~ How to reset C _36-48 and switch T ₁ ~
The point is to provide means for resetting the ground capacitance C _W of the wiring between T ₄₈ and the amplifier AMP.

Storage capacitors C _{1-1 to} C of the first block
_The signal charges accumulated in _1-48 are applied to the gate pulse P _G11 from the shift register SR3 through the gate line G ₁ during the period t ₁₆ in which T _{1-1 to} T _1-48 of the transfer TFT are in the ON state. Switch R to which the control pulse P _Q is applied
During the period t ₁₇ in which _{1 to} R ₄₈ are in the off state, they are transferred to the ground capacitances C _{L1 to} C _L48 of the matrix signal lines L _{1 to} L ₄₈ .
Subsequently, the signal charges in the first block are transferred to the read capacitors C _{T1 to} C _T48 through the switches U _{1 to} U ₄₈ in the period t ₃ . After the time period t ₃ , the switch R ₁ is turned on during the time period t _16.
During the period t ₁₈ during which R ₄₈ is on, the storage capacitor C
The ground capacitances C _{L1 to} C _L48 of _{1-1 to} C _1-48 and the matrix signal wirings L _{1 to} L ₄₈ are reset by the DC power supply V _R. Similarly, the signal charge of the second block is the period T ₁₉ during which T _{2-1 and the} like of the transfer TFT of the second block is in the ON state.
Of the matrix signal wirings L _{1 to} L _{48 to} the ground capacitances C _{L1 to} C _L48 during the period t ₂₀ in which the switches R _{1 to} R ₄₈ are off.
It is transferred to and subsequently read capacitor C _T1 to period t ₉ by ~
Forwarded to C _T48 . After a further period t _9, the period t ₂₁ the switch R ₁ to R ₄₈ is in the on state in the period t _19,
The storage capacitor C _2-1 of the second block is a DC power source V
Reset by _R.

When the capacitance C _W to ground of the wiring between the switches T _{1 to} T ₄₈ and the amplifier AMP has a capacitance value which is not negligible compared with the read capacitors C _{T1 to} C _T48 , the read capacitors C _T1 to C. _Since the signal charge read from any one of _T48 remains in the ground capacitance C _W , it becomes a noise charge with respect to the signal charge read next from any of the read capacitors C _{T1 to} C _T48 . To prevent this, time t ₂₂ none of the switches T ₁ through T ₄₈ are off,
During a period such as t ₂₃ , the switch W to which the control pulse P _W is applied is turned on, and the ground capacitance C _W is reset by the DC power supply V _R.

[0015]

As described above, according to the present invention, noise charges are uniform and reduced by resetting all the plurality of reading capacitors at the same time and immediately before the next signal charge is transferred. , S / N has the effect of obtaining a good image signal output.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing a timing chart at the time of operation of the first embodiment shown in FIG.

FIG. 3 is an equivalent circuit diagram of a second embodiment of the present invention.

FIG. 4 is a diagram showing a timing chart at the time of operation of the second embodiment shown in FIG.

FIG. 5 is an equivalent circuit diagram of an example of a conventional contact image sensor.

FIG. 6 is a diagram showing a timing chart during operation of the conventional contact image sensor shown in FIG.

[Explanation of symbols]

 1,4 Photoelectric conversion unit 2,5 Drive switch unit 3,6,7 Read switch unit

Claims (3)

[Claims] 1. A plurality of photoelectric conversion elements arranged in an array are divided into a plurality of blocks by dividing a plurality of signal charges generated in response to incident light from the outside. As a parallel image signal, the parallel image signals transferred to the respective readout capacitors are sequentially read out after being collectively transferred to the readout capacitors individually provided in the matrix signal wirings connected to the photoelectric conversion elements. In a contact image sensor having a matrix signal wiring structure configured to sequentially perform the operation of converting a parallel image signal into a serial image signal and outputting the serial image signal, in a batch transfer of the parallel image signal to the reading capacitor. Immediately before, the means for resetting all of the reading capacitors to the same voltage at the same time is provided. Contact image sensor. 2. An array of a plurality of unit circuits each including at least a photoelectric conversion element, a storage capacitor for storing signal charges generated in the photoelectric conversion element, and a transfer transistor for transferring the stored signal charge. And a plurality of signal wirings for outputting the signal charges from each unit circuit in parallel in units of the blocks obtained by dividing the photoelectric conversion array into a plurality of blocks, and turning on the transfer transistor. A photoelectric conversion part formed by forming an off control signal wiring on the same substrate; and a block control means for sequentially selecting each block by performing on / off of the plurality of transfer transistors in the block unit. , A plurality of transfer switches individually connected to each of the signal wirings and collectively controlled so as to simultaneously connect and disconnect the signal wirings. H, a plurality of read capacitors individually connected to the output points of the respective transfer switches, and terminal voltages of the respective read capacitors individually connected to the respective read capacitors so as to be sequentially transferred to the common output point. Read-out means including at least a plurality of read-out switches sequentially controlled, and a parallel image signal output in block units to the signal wiring is converted into a serial image signal by the read-out means and output to the outside. In the contact-type image sensor having a configuration in which blocks are sequentially switched, a means for resetting all the reading capacitors to the same predetermined voltage all at once at the timing immediately before the timing when the transfer switch is turned on is provided. A contact image sensor characterized by being provided. 3. The contact image sensor according to claim 2, further comprising means for resetting the potential at the common output point to a predetermined potential within a period in which all the read switches are in the off state. Adhesive image sensor.