JPH0568139A - Image reader - Google Patents

Abstract

PURPOSE:To prevent the reading shift of picture elements in each block in a sub-scanning direction and a reading shift on a node between plural sensors by connecting a batch transfer switching element and a batch transfer capacitor between a photodetecting element and a switching element. CONSTITUTION:The batch transfer TFT 21' and the batch transfer capacitor 22' are connected between the photodetecting element 11' and a block selecting/ transferring TFT 12' to execute the batch transfer of signal charges. Since all picture elements on the same line of a read image signal are simultaneously read out, the generation of a reading shift in each block can be prevented. Even when plural sensors are connected in the main scanning direction, the generation of a shift on a node between sensors arranged in the subscanning direction can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus used for an image input apparatus such as a facsimile, a scanner, a digital copier, an optical character reading apparatus, etc., and in particular, a plurality of image sensors at the reading portion are arranged in the main scanning direction. However, the present invention also relates to an image reading device that eliminates the deviation of reading in the sub-inspection direction.

[0002]

2. Description of the Related Art Among conventional image sensors, in particular, a contact image sensor projects image information of a document or the like on a one-to-one basis and converts it into an electric signal. In this case, the projected image is divided into a large number of pixels (light receiving elements), and the charges generated in each light receiving element are transferred to a thin film transistor switch (TF).
There is a TFT drive type image sensor which temporarily stores in a capacity between wirings in a specific block unit using T) and sequentially reads out as an electric signal in time series at a speed of several hundred KHz to several MHz.

This TFT drive type image sensor is
The operation of T makes it possible to read with a single driving IC, so that the number of driving ICs driving the image sensor is reduced.

The TFT drive type image sensor is, for example,
As shown in the equivalent circuit diagram of FIG. 5, a line-shaped light receiving element array 11 having a length substantially the same as the document width and each light receiving element 1 are provided.
A plurality of thin film transistors Ti corresponding to 1'to 1: 1,
The charge transfer portion 12 is composed of j (i = 1 to N, j = 1 to n) and the matrix-shaped multilayer wiring 13.

The light-receiving element array 11 is divided into light-receiving element groups of N blocks, and the n light-receiving elements 11 'forming one light-receiving element group are photodiodes Pi, j (i
= 1 to N, j = 1 to n). Each light receiving element 11 'is connected to the drain electrode of each thin film transistor Ti, j, and each thin film transistor Ti, j
The source electrode of j is connected to n common signal lines 14 for each light receiving element group via the multilayer wiring 13 formed in a matrix, and the common signal line 14 is further connected to the driving IC 1
Connected to 5.

A gate generation circuit 16 is connected to the gate electrode of each thin film transistor Ti, j so as to be conductive in each block. The photocharge generated in each light receiving element 11 'is for a certain period of time and the parasitic capacitance of the light receiving element and the thin film transistor Ti, j
After being accumulated in the overlap capacitance between the drain and the gate, the thin film transistors Ti, j are sequentially transferred to the wiring capacitance Ci (i = 1 to n) of the multilayer wiring 13 for each block by using the thin film transistor Ti, j as a charge transfer switch. Accumulated.

That is, the gate pulse .phi.G1 from the gate pulse generation circuit 16 turns on the thin film transistors T1,1 to 1, n in the first block, and the thin film transistors T1,1 to 1, n in the first block are generated and accumulated in the respective light receiving elements 11 'in the first block. The accumulated charge is transferred and accumulated in each wiring capacitance Ci. Then, the electric potential of each common signal line 14 changes due to the charges transferred and accumulated in each wiring capacitance Ci, and the voltage value is set in a time series by sequentially turning on the analog switches SWi (i = 1 to n) in the driving IC 15. Output line 1
7 is extracted.

Then, next, gate pulses φG2 to φGn
Accordingly, the thin film transistors T2,1 of the second to Nth blocks are
-T2, n to TN, 1 to TN, n are turned on respectively to transfer charges on the light receiving element side for each block,
An image signal of one line in the main scanning direction of the original is obtained by sequentially reading, and the original is moved by an original feeding means (not shown) such as a roller to repeat the above operation to obtain an image signal of the entire original. (See JP-A-62-67869).

[0009]

When it is attempted to read an original at a higher speed by using the conventional one-dimensional TFT driving type image sensor of the sequential signal reading type, a plurality of the one-dimensional image sensors are arranged in the main scanning direction. It was considered to arrange them in parallel and perform parallel reading. Further, in the case of producing a long sensor of A0 size or the like, it was necessary to similarly connect several one-dimensional TFT drive type image sensors of the sequential signal reading type in parallel in the main scanning direction and read them.

However, in the image reading apparatus in which the one-dimensional TFT driving type image sensors of the sequential signal reading method are connected in parallel in the main scanning direction and arranged, as shown in the schematic diagram of image reading in FIG. There is a problem in that a pixel reading shift may occur in the sub-scanning direction at a joint between the sensor and an adjacent image sensor in parallel, which prevents a higher resolution in the sub-scanning direction.

The deviation in the sub-scanning direction as shown in FIG. 6 is caused by the one-dimensional TFT drive type image sensor reading pixels in the main scanning direction in block units, while the original or the image sensor is relatively moved in the sub-scanning direction. In order to move the image sensor, the read pixel position is different in the sub-scanning direction between the first read block and the last read block in one image sensor. Especially, the sub-scanning position is the most in the part where the image sensors are connected. The deviation of the direction had come to appear greatly.

The present invention has been made in view of the above circumstances, and in the case of an image sensor connected in parallel, the signal charges are collectively transferred to a newly provided capacitor before the signal is sequentially read out to the driving IC. By further performing the above operation and sequentially transferring to the capacitance between the signal lines, it is possible to provide an image reading apparatus capable of eliminating a pixel reading deviation for each block in the sub-scanning direction and a pixel reading deviation at a sensor connecting portion. The purpose is to do.

[0013]

DISCLOSURE OF THE INVENTION The present invention for solving the above-mentioned problems of the prior art includes a light receiving element array in which a plurality of light receiving elements are set as one block and the plurality of blocks are arranged in the main scanning direction. In the image reading apparatus, the image sensor is formed so that the light receiving element array is arranged in plural in the main scanning direction, the image sensor having a switching element that is connected to each other and transfers the charge generated in the light receiving element in the block unit. A capacitor for collective transfer for collectively transferring charges of the light receiving element is provided between the light receiving element and the switching element, and charges of all light receiving elements are provided between the light receiving element and the batch transfer capacitor. Is provided with a batch transfer switching element that transfers the data to the batch transfer capacitor at the same timing.

[0014]

According to the present invention, a plurality of light receiving element arrays are arranged in the main scanning direction in an image sensor having a plurality of light receiving element arrays each having a plurality of light receiving elements as one block and a switching element connected to each of the light receiving elements. In the image reading apparatus formed as described above, a switching element for batch transfer for collectively transferring the charges generated in the light receiving element between the light receiving element and the switching element and a batch transfer for transferring the charges collectively Since all the pixels of one line in the main scanning direction of the image reading device can be read at the same timing because of the provision of the above capacity, the pixel reading error in the block unit in the sub scanning direction and the reading at the joint of the sensor are performed. The gap can be eliminated.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an equivalent circuit diagram of one image sensor according to an embodiment of the present invention. It should be noted that parts having the same configurations as those in FIG.

In the image sensor of this embodiment, a plurality of light receiving elements 11 'are set as one block, and a light receiving element array 11 composed of a plurality of (first to Nth) blocks and a light receiving element 11'.
A switching element 21 'for batch transfer and a capacitor (CL') 22 'for batch transfer are formed on the signal lines respectively drawn from the plurality of switching element arrays 21 and batch transfer switching element array 21 and batch transfer in the main scanning direction. And a capacitance array 22.

Further, a block selection / transfer switching element 12 'for transferring charges for each block is provided so as to be connected to the collective transfer capacitor 22', and a block selection / transfer switching element 12 'is provided. Are arranged in the main scanning direction to form the block selection / transfer switching element array 12. The signal line extracted from the block selection / transfer switching element 12 ′ is connected to the multilayer wiring 13 of the matrix structure, and the multilayer wiring 1
A common signal line 14 for the number of light receiving elements in one block is extracted from 3 and connected to an analog multiplexer of the driving IC 15. A load capacitance (CL) is formed on each common signal line 14. The gate voltages VG1 to VGn are applied to the block selection / transfer switching element 12 'in block units.

The structure of the light receiving element 11 'of this embodiment is such that a metal electrode made of chromium (Cr) formed on a substrate and an indium tin oxide (IT) formed as an individual electrode.
A) and a transparent electrode made of amorphous silicon (a
-Si) sandwiched between photoconductive layers.

Further, the switching element 2 for batch transfer
1'and block selection / transfer switching element 12 '
In the configuration, a gate electrode of Cr, a gate insulating layer of silicon nitride (SiNx), a semiconductor active layer of a-Si, and a channel protective layer of SiNx are sequentially laminated on the substrate, and n + amorphous silicon is sandwiched between the channel protective layers. (N + a-S
i) Inverse stagger type thin film transistor (T) in which the ohmic contact layer and the source / drain electrodes of Cr are formed.
FT).

A positive (+) bias voltage is applied to the common electrode of the light receiving element 11 'so that the bias voltage VB becomes a reverse bias with respect to the photodiode. The voltage VGT applied to the batch transfer switching element 21 'is a batch transfer gate pulse, and the voltages VG1 ... VGn applied to the block selection / transfer switching element 12' are block selection gate pulses. Has become.

The configuration of the light receiving element, the batch transfer switching element (batch transfer TFT), the batch transfer capacitor, and the block selection / transfer switching element (block selection / transfer TFT) of the image sensor of this embodiment is shown in FIG. Two
Will be described with reference to the plan explanatory diagram of

An aluminum (Al) wiring 30a is drawn out from the transparent electrode 25 serving as an individual electrode of the photodiode (light receiving element) 11 'and connected to the drain electrode 31a of the batch transfer TFT 21'. The source electrode 32a of the batch transfer TFT 21 'is the Al wiring 30b.
Connected to one end of the batch transfer capacitor 22 'via
The other end of 2'is connected to the drain electrode 31b of the block selection / transfer TFT 12 '. Also, block selection
The Al wiring 30c extracted from the source electrode 32b of the transfer TFT 12 'is connected to the matrix-shaped multilayer wiring 13.

The metal electrode 2 of the photodiode 11 '
4 is formed in a strip shape in the main scanning direction, serves as a common electrode for the array, and is applied with a bias voltage VB. The batch transfer capacitor 22 'has a structure in which an insulating layer is sandwiched between a lower electrode formed of Cr or the like and an upper electrode formed of Al or the like.

Next, the operation of the image reading apparatus of this embodiment will be described with reference to the timing chart of FIG. 3 and FIG. The bias voltage VB is applied with a voltage of 5 V, and the photodiode of the light receiving element is in the reverse bias state of the Schottky diode.

The electron-hole pairs generated in the photodiode during the accumulation time are accumulated and become signal charges.
This signal charge is transferred to the gate electrode 3 of the batch transfer TFT 21 '.
By applying a gate pulse of the voltage VGT to 3a, all blocks are simultaneously transferred to the batch transfer capacitance array 22 at the same time. When a plurality of light receiving element arrays 11 of the image sensor are arranged in the main scanning direction, the batch transfer TFTs of all the image sensors are operated at the same timing.

The signal charges transferred to each batch transfer capacitor 22 'are block selection / transfer TFTs for each block.
By sequentially applying the gate pulses of the voltages VG1 to VGn to the gate electrode 33b of 12 ', the signal charges are sequentially transferred to the analog multiplexer of the driving IC 15 in block units. As shown in FIG. 3, the timing of the gate pulse of the voltage VGT and the gate pulse of the voltages VG1 to VGn is such that the voltages VG1 to VGn are sequentially applied after the voltage VGT is collectively turned on.

Considering an image reading apparatus in which a plurality of light receiving element arrays of this embodiment are arranged in the main scanning direction, the voltage VGT is the batch transfer TFT 2 of all image sensors.
By turning on the gate electrodes 1'at the same time, it is possible to eliminate the shift in the sub-scanning direction at the joint between the plurality of image sensors.

The capacity of the batch transfer capacity 22 '(C
L ') is expressed by the capacity decomposition ratio = CL' / (CL '+ CP) from the relationship with the additional capacitance (CP) of the photodiode, so that CP <<<<CL' in order to increase the transfer efficiency. However, in the present embodiment, since it is a two-stage transfer of batch transfer and block transfer, the batch transfer capacitor (CL ') 22' to the load capacity (CL) of the common signal line is used.
However, in order to increase the sensitivity, the value of the batch transfer capacity (CL ') should be smaller than the load capacity (CL) of the common signal line. Can be improved. That is, the value of the batch transfer capacitance (CL ') is made larger than the additional capacitance (CP) of the photodiode, but is made smaller than the value of the load capacitance (CL) of the common signal line.

However, depending on the relationship between the capacitance (CL ') of the batch transfer capacitor 22' and the load capacitance (CL) of the common signal line, the signal charges that are not transferred may be the batch transfer capacitor 22 '.
Therefore, it is conceivable that a thin film transistor switching element for signal reset (signal reset TFT) is further provided in the collective transfer capacitor 22 'to reset the residual charge.

FIG. 4 shows an equivalent circuit diagram of an image sensor with a signal reset TFT. The voltage VGT is a gate pulse for batch transfer, and the voltage VGR is a gate pulse for reset. As for the operation timing, as shown in FIG. 3, the block selection / transfer TFT 12 'is sequentially turned on for each block, and the charge of the batch transfer capacitor 22' is driven by the driving IC 15.
After the transfer is completed, all the signal reset TFTs 23 are turned on at the same time to reset all the batch transfer capacitors 22 '.

According to the image reading apparatus of the present embodiment, the batch transfer TFT 21 'and the batch transfer capacitor 22' are added between the light receiving element 11 'and the block selection / transfer TFT 12' to generate the signal charge. By performing the batch transfer, the read image signals read the same line for all pixels at the same time, so it is possible to eliminate the reading misalignment in block units, and even when the sensors are connected in the main scanning direction. There is an effect that the shift of the joint between the sensors in the scanning direction can be eliminated, and high resolution in the sub-scanning direction can be achieved at high speed operation.

Further, the signal reset TFT shown in FIG.
According to the image reading apparatus of another embodiment provided with the reset transfer TFT 23 in the batch transfer capacitor 22 ', the batch transfer capacitor 22' remains in the batch transfer capacitor 22 'without being transferred to the load capacitance of the common signal line. Since the charges can be removed by the reset operation of the reset TFT 23, afterimages in reading can be removed and accurate signal charges can be output, and the image reading apparatus can be improved in performance.

[0033]

According to the present invention, a light receiving element array including a plurality of light receiving elements as one block,
In an image reading apparatus in which an image sensor having a switching element connected to each light receiving element is formed so that a plurality of light receiving element arrays are arranged in the main scanning direction,
An image reading device is provided between the light receiving element and the switching element, since a batch transfer switching element for collectively transferring the charges generated in the light receiving element and a batch transfer capacitor for collectively transferring the charges are provided. Since it is possible to read all the pixels of one line in the main scanning direction at the same timing, it is possible to eliminate the pixel misalignment in block units in the subscanning direction and the misalignment at the joints of the sensors. There is an effect that high resolution can be achieved.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram of an image sensor according to an embodiment of the present invention.

FIG. 2 is an explanatory plan view of the image sensor of this embodiment.

FIG. 3 is a timing diagram of gate pulses.

FIG. 4 is an equivalent circuit diagram of another embodiment.

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

FIG. 6 is a schematic diagram of image reading by an image sensor.

[Explanation of symbols]

11 ... Light receiving element array, 12 ... Block selecting / transfer switching element array, 13 ... Multi-layer wiring, 14 ...
Common signal line, 15 ... Driving IC, 16 ... Gate pulse generating circuit, 17 ... Output line, 21 ... Batch transfer switching element array, 22 ... Batch transfer capacitor, 23
... signal reset TFT, 24 ... metal electrode, 25 ...
Transparent electrode, 30 ... Wiring, 31 ... Drain electrode, 3
2 ... Source electrode

Claims (1)

[Claims] 1. A light receiving element array in which a plurality of light receiving elements are set as one block and a plurality of blocks are arranged in the main scanning direction, and a switching which connects to each of the light receiving elements and transfers charges generated in the light receiving elements in the block unit. In an image reading apparatus in which an image sensor having an element is formed such that the light receiving element array is arranged in a plurality in the main scanning direction, electric charges of the light receiving element are collectively stored between the light receiving element and the switching element. And a batch transfer switching element that transfers the charges of all the light receiving elements to the batch transfer capacitors at the same timing between the light receiving elements and the batch transfer capacitors. An image reading device characterized by being provided.