JPH0548842A - Original reader - Google Patents

Abstract

PURPOSE:To accurately read out the electric signal of each photoelectric conversion element by arranging two or more channel wiring groups and connecting respective photoelectric conversion elements in adjacent blocks to different channel wiring groups. CONSTITUTION:Two channel wiring groups G1 and G2 to lead out electric signals of photo diodes PD with a block as the unit are arranged, and anode electrodes of photo diodes PD are alternately connected to different channel wiring groups G1 and G2 with each of blocks B1, B2,... Bm as the unit. Therefore, electric signals of photo diodes PD as photoelectric conversion elements are read out in order with a block as the unit, but electric signals of photo diodes PD in each block is read out through the channel wiring group other than the channel wiring group through which electric signals of photo diodes PD in the preceding block the are read out. Consequently, an influence of switching noise for read of electric signals of photo diodes PD in the preceding block is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading device, and more particularly to a document reading device used in a reading unit such as a facsimile, an image scanner, a digital copying machine, and an electronic blackboard.

[0002]

2. Description of the Related Art Conventionally, a document reading apparatus of a reduction optical system using a charge coupled device (CCD) has been used in a reading section of a facsimile or the like.
Such a document reading device is generally called an image sensor, and in recent years, a contact image sensor capable of reading a document at a normal size has been used. The contact-type image sensor is configured by arranging a plurality of photoelectric conversion elements such as photodiodes one-dimensionally on a glass substrate, and usually adopts a matrix driving method in which the number of switching elements is small.

As shown in FIG. 5, a matrix drive type document reading apparatus has m × n photodiodes PD arranged one-dimensionally, and blocking diodes BD are connected in series in reverse polarity to these photodiodes PD. There is. The photodiode PD and the blocking diode BD are divided into m blocks B _1, B _2, ... B _m every n blocks _{, and} the anode electrode of the blocking diode BD is each block B _1, B _{2 ,.} ... B _m are connected to common block wirings A _1, A _2, ... A _m , while the anode electrode of the photodiode PD is connected to each block B.
Channel wirings C _1, C _2, ... C _n that are relatively common to each other among _1, B _2, ... B _m are connected to each other. The entire channel wirings C _1, C _2, ... C _n block the electric signals of the photodiode PD B _1, B _{2 ,} .
A channel wiring group G for leading out in units of _m is configured.

This document reading device is operated in a so-called charge accumulation mode, and each block wiring A _1,
Drive ICs for sequentially applying drive pulses to the blocks B _1, B _2, ... B _m are connected to A _2, ... A _m , and the channel wirings C _1, C _{2 ,} . .. C _n is used by being connected to a reading IC for reading the electric signal of the photodiode PD.

As shown in the time chart of FIG. 2, when drive pulses are sequentially applied from the first block B ₁ by the drive IC, the blocks B _1, B _2, ... B _m are turned on in order. And block B turned on.
The electric signals of the photodiodes PD in _1, B _2, ... B _m are converted into the respective channel wirings C _1, C _2, ... C _n.
And read by the reading IC. In other words, this document reading device is of a type that reads out the electric signal of the photodiode PD in units of blocks B _1, B _2, ... B _m .

[0006]

However, in such a document reading apparatus, switching noise when the previous block is read, capacitive noise due to the fall of the previous drive pulse, and the like are generated in the next block. However, there is a problem that the next block is not accurately read because it remains until the next block is read. On the other hand, it may be possible to reduce the influence from the previous block by lengthening the interval t ₁ of each drive pulse, but the reading time per line becomes longer and the reading speed as a whole becomes slower. There are drawbacks.

Therefore, the present inventors have conducted intensive studies to reduce the influence of the previous block on the next block without increasing the reading time per line, and as a result, the present invention has been achieved.

[0008]

A document reading apparatus according to the present invention is characterized in that at least a plurality of photoelectric conversion elements are arrayed one-dimensionally and are divided into a plurality of blocks at a fixed number. A document reading apparatus for sequentially reading the electric signals of the conversion elements in units of the blocks, wherein at least two groups of channel wirings for deriving the electric signals of the photoelectric conversion elements in the units of blocks are arranged, and in adjacent blocks. That is, each photoelectric conversion element in is connected to a different channel wiring group.

[0009]

According to such an original reading apparatus, the electric signals of the photoelectric conversion elements are sequentially read in block units. However, the electric signals of the photoelectric conversion elements in any block are always read in the previous block. The electric signal of the photoelectric conversion element is read out through a channel wiring group different from that when the electric signal is read out. Therefore, the influence of switching noise or the like when the electric signal of the photoelectric conversion element in the previous block is read is reduced, and the electric signal of each photoelectric conversion element in any block is always read accurately.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the document reading apparatus according to the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, in the document reading apparatus according to the present invention, m × n photodiodes PD and blocking diodes BD connected in series to them in reverse polarity are arranged one-dimensionally. Thus, the n photodiodes PD and the blocking diodes BD are set as one unit and are divided into _m blocks B _1, B _2, ... B _m . These photodiodes PD are photoelectric conversion elements formed by stacking semiconductor thin films such as amorphous silicon a-Si in a pin structure or the like. Normally, the blocking diode BD is also formed at the same time as these photodiodes PD and has the same structure. ing. These blocking diodes BD are provided for each block B during reading.
It is a switching element for preventing crosstalk in _1, B _2, ... B _m .

[0012] The anode electrode of the blocking diode BD is connected to common blocks B _1, B _2, ... in B _m by the block wiring _{A 1, A 2, ... A} m. On the other hand, the anode electrode of the photodiode PD is the block B _1, B
Channel wiring groups G _{1 and} G that are alternately different in units of _2, ... B _m
Connected to ₂ . That is, the first block B ₁ , the third block
Of the photodiode PD in the block B ₃ , the fifth block B ₅ , the seventh block B ₇ , ... Of the m−1th block B _m−1 , the first channel wiring group G Each channel wiring C ₁₁ , which composes ₁ ,
By C ₁₂ , ... C _1n , these blocks B _1, B _3, B _5, B
_7, ... B _m-1 , which are relatively in the same position, are commonly connected to each other, and the second blocks B ₂ ,
The anode electrodes of the photodiodes PD in the block B ₄ , the sixth block B ₆ , the eighth block B ₈ , ... In the m-th block B _m form a _second channel wiring group G _2. Each channel wiring C ₂₁ , C ₂₂ , ...
By C _2n , these blocks B _2, B _4, B _6, B _8, ... B _m
Those that are relatively in the same position are commonly connected to each other.

This document reading apparatus can also be operated in the charge storage mode as in the conventional apparatus, and each block wiring A _1, A _2, ... _Am has each block B _1, B _{2 ,.} ...
A driving IC for sequentially applying a driving pulse for each B _m is connected, and a reading IC for reading an electric signal of the photodiode PD is connected to each channel wiring group G _{1 and} G ₂ for use. To be done.

As shown in the time chart of FIG. 2, the first
Block B ₁ , second block B ₂ , third block B ₃ , ... mth block B _m , first block B ₁ ,
The driving pulse is the driving pulse I in the order of the second block B ₂ , ...
It is applied by C and turns on. Electrical signals of the photodiodes PD in this block was turned on B _1, B _2, ... in B _m is the block B
Channel wiring group G that is alternately different in units of _1, B _2, ... B _m
It is read by the reading IC through _{1 and} G ₂ .

To explain step by step, first, when a drive pulse is applied to the first block B ₁ to turn it on, each photodiode PD in this block B ₁ is
A signal current corresponding to the image information accumulated until then flows. These signal currents are amplified and integrated by the reading IC through the _first channel wiring group G ₁ and serially output, and the electric signal of each photodiode PD in this block B ₁ is read. At this time, the other blocks B _2, B _3, ... B _m are in the off state, and a signal current flows through each photodiode PD in these blocks B _2, B _3, ... B _m . Therefore, only the first block B ₁ will be selectively read.

Next, when a drive pulse is applied to the second block B ₂ to turn it on, this block B ₂ is also turned on.
_A signal current flows through each photodiode PD in ₂ and is read out through the _second channel wiring group G ₂ this time. Therefore, it is affected by switching noise generated when the previous first block B ₁ is read out and capacitive noise generated when the drive pulse applied to the previous first block B ₁ falls. Therefore, the electric signal of each photodiode PD in the second block B ₂ is accurately read.

Next, the electric signal of each photodiode PD in the third block B ₃ is read again via the _first channel wiring group G ₁ , but at this time,
Sufficient time t since the first block B ₁ was read
_{Since 2} has passed and the switching noise and the like generated when the first block B ₁ is read have already disappeared, there is no influence from the _first block B ₁ . Further, similarly to the above, there is no influence from the _second block B ₂ .

Hereinafter, the fourth block B _{4 and the} subsequent blocks are similarly read, but the photodiodes PD in the respective blocks B _4, B _5, ... Are not affected by the previous block. The electric signal can be read accurately. Further, although the drive pulse interval t ₁ is the same as the conventional one, the influence of the previous block on the next block can be reduced. That is, the original can be read more accurately while maintaining the conventional reading speed per line.

In the present embodiment, the number m of blocks and the number n of photodiodes in one block are generally expressed. However, for example, in the case of an A4 size document reading device having a resolution of 8 dots / mm. , 1728 photodiodes PD are required, and normally 32 photodiodes are divided into 54 blocks.

Although one embodiment of the document reading apparatus according to the present invention has been described in detail above, the present invention is not limited to the above-mentioned embodiment and can be implemented in other modes.

For example, as shown in FIG. 3, the present invention can be applied to an original reading device of a type selectively driven by a thin film transistor TFT instead of a blocking diode. In this case, the anode electrode of the photodiode PD, the block B _1, B _2, ... be connected via the TFT to the different channels interconnect group G _1, G ₂ alternately at B _m units, while the photodiode PD The cathode electrodes of are all connected to a common drive power source E. The gate electrode of the TFT block wiring A _1, A _2, are connected in common in each block by · · · A _m.

Although not shown, the present invention can also be applied to a photoconductive type document reading apparatus using CdS-CdSe or the like as a photoelectric conversion element. In this case, unlike the charge storage type described above, a blocking diode or a TFT is used.
A switching element such as is not particularly required, and at least a photoconductive photoelectric conversion element may be arranged.

Although not shown, three or more channel wiring groups are arranged, the first block is the first channel wiring group, the second block is the second channel wiring group, and the second block is the second channel wiring group. The third block may be connected to the third channel wiring group, and so on. In short, if each photoelectric conversion element in the adjacent block is connected to a different channel wiring group, the electric signal of the photoelectric conversion element can be accurately read without being affected by the previous block. .

Further, it is naturally applicable to an A4 size document reading device having a resolution of 16 dots / mm, but in this case, 3456 photodiodes are required, so that the same reading speed as the conventional one can be obtained. In order to realize it with a conventional document reading apparatus, there is no choice but to halve the width of the drive pulse. However, in the present invention, since the electric signal of the photodiode is read alternately through independent channel wiring groups in block units, as shown in FIG. 4, each drive pulse has the same drive pulse width as in the conventional case. Just make a little overlap. Therefore, it is not necessary to use a particularly expensive IC.

It is preferable that the channel wiring group is formed on the same plane on the same glass substrate.
The second channel wiring group may be formed on the above channel wiring group to form a laminated structure.

Alternatively, the anode electrodes of the blocking diode and the photodiode may be connected to each other, the cathode electrode of the blocking diode may be connected to the block wiring, and the cathode electrode of the photodiode may be connected to the channel wiring. Further, a photodiode may be connected to the block wiring side and a blocking diode may be connected to the channel wiring side. For example, various improvements, corrections, and modifications can be made on the basis of the knowledge of those skilled in the art without departing from the gist of the present invention. Can be carried out.

[0027]

In the document reading apparatus according to the present invention, at least two groups of channel wirings are arranged and each photoelectric conversion element in the adjacent block is connected to a different channel wiring group. The electric signal of each photoelectric conversion element in the block can be accurately read. Further, since the influence from the previous block can be reduced without increasing the drive pulse interval, not only can the reading speed per line so far be maintained, but the reading speed can be further increased. It is also possible. On the contrary, it is possible to improve the resolution by increasing the number of photoelectric conversion elements while maintaining the reading speed per line so far, which is an excellent effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a document reading apparatus according to the present invention.

FIG. 2 is a time chart showing drive pulses in the conventional document reading apparatus shown in FIG.

FIG. 3 is a circuit diagram showing another embodiment of the document reading apparatus according to the present invention.

FIG. 4 is a time chart showing drive pulses in another embodiment of the document reading apparatus according to the present invention.

FIG. 5 is a circuit diagram showing an example of a conventional document reading apparatus.

[Explanation of symbols]

PD: Photodiode (photoelectric conversion element) BD: Blocking diode A ₁ , A ₂ , ... _Am ; Block wiring B ₁ , B ₂ , ... B _m ; Block G ₁ , G ₂ ; Channel wiring group C Channel wiring ₁₁ , C ₁₂ , ... C _1n , C ₂₁ , C ₂₂ , ... C _2n

Claims (1)

[Claims] 1. An original reading device in which at least a plurality of photoelectric conversion elements are arranged one-dimensionally and divided into a plurality of blocks at a fixed number, and an electric signal of the photoelectric conversion elements is sequentially read in block units. At least two groups of channel wirings for deriving the electric signal of the photoelectric conversion element in the block unit are arranged, and each photoelectric conversion element in an adjacent block is connected to a different channel wiring group. Document reading device.