JPH04109753A - Image sensor and its drive method - Google Patents

Abstract

PURPOSE:To implement read of a picture signal and an idle read within a scanning time of one line by providing a switch connected selectively to a read circuit, a bias power supply or a ground line to a group common electrode of each light receiving element group and implementing matrix drive. CONSTITUTION:Each analog switch 9n is controlled by three control pulses so that a group common electrode 8n is connected to a common wiring 5, a bias power supply 6 or a ground line 10. A shift register SR applies a drive pulse sequentially and each picture signal is extracted in time series from a light receiving element 1 of a 2nd block. In this case, a light receiving element group 31 of a 1st block is connected to the ground line 10 by an analog switch 91. When the drive pulse is sequentially applied to the light receiving elements forming the 2nd block, the drive pulse is applied also to the light receiving element group 31 of the 1st block (for matrix drive) and idle read of each light receiving element 1 of the light receiving element group 31 is sequentially implemented, That is, the read of the light receiving element group 3n of the n-th block and also idle read of light receiving element group 3n-1 of the (n-1)th block are implemented simultaneously.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an image sensor used in an input section of a facsimile machine, etc., and particularly includes a plurality of light receiving elements each having two diodes connected in series with opposite polarities. The present invention relates to an image sensor formed by arranging light receiving elements in a line to form an array of light receiving elements, and a method for driving the same.

(Prior Art) Conventionally, an image sensor used for image reading in a facsimile machine, etc., has a photodiode PD and a blocking diode BD connected in series so that the polarities are opposite to each other, as shown in FIG. 3, for example. A plurality of light receiving elements 1 are arranged in a line to form one light receiving element 1.
It constitutes array 2. In the image sensor shown in FIG. 3, in order to reduce the number of drive ICs, the light-receiving element array 2 is divided into a plurality of light-receiving element groups 3n each consisting of an aggregate of light-receiving elements 1, and these light-receiving element groups 3n are divided into one The integrator 4 (reading circuit) sequentially selects the light receiving elements n13n by matrix driving using the shift registers SR.
, and reads the signals of each light receiving element 1 constituting the light receiving element group 3n.

Image signals from the image sensor having this structure are read out as follows.

That is, one of the plurality of light-receiving element groups 3n is connected to the common wiring 5 by the block selection switch 7n, and in this state, each light-receiving element 1 constituting the light-receiving element group 3n is scanned by the shift register SR to sequentially receive a signal. is applied, charges are charged to the photodiode PD, and after the signal is applied, both the photodiode PD and the blocking diode BD are in a reverse bias state. At this time, other photodetector rRT
The blocking diode BD 3n is connected to the bias power supply 6 by a block selection switch 7n, and a reverse bias potential is applied to the blocking diode BD in order to prevent the occurrence of crosstalk within the group of light receiving elements.

The above operation is performed for each light-receiving element group 3n by switching f1 or the block selection switch 7n, and the photodiodes P of all the light-receiving elements 1 constituting the light-receiving element array 2 are
D1. : Electric charge is charged.

During one scan cycle, the photodiode PD is irradiated with light, and a photocurrent corresponding to the amount of irradiated light causes a charge to be discharged. In other words, a charge corresponding to the amount of light is accumulated between the photodiode PD and the blocking diode BDO. will be done.

Then, a read pulse is sequentially applied to each light receiving element by the same operation again by the shift register SR, each photodiode PD is recharged with a charge corresponding to the discharge amount, and the current flowing due to recharging is transferred to the integrator 4 ( Each image signal is extracted in time series by reading it through a reading circuit (reading circuit).

According to the image sensor of the above method, since the switching characteristics of the blocking diode BD are structurally poor, the photodiode PD is not completely recharged, and residual charges are generated. Therefore, in the next reading scan, the newly accumulated charge and the residual charge will be read out, and an afterimage component will be included. Further, since this afterimage component changes depending on the amount of incident light, there is a drawback that it causes an error in the output signal.

Therefore, an image sensor has been proposed in which a light source that directly irradiates the light receiving element array is newly provided, and the photodiode PD is irradiated with the light source prior to storage and reading scanning to perform blank reading.

According to this image sensor, the state of the photodiode PD immediately before charge current accumulation starts is the state after photocurrent is accumulated under a substantially constant amount of incident light and an idle reading is performed. , the voltage between the photodiode PD and the blocking diode BD can be maintained at a substantially constant value, thereby preventing errors from occurring in the output signal (see Japanese Patent Laid-Open No. 58127465).

(Problem to be Solved by the Invention) However, according to the above image sensor driving method,
Since the photodiode PD is irradiated with a light source for each scan to perform blank reading, there is a problem in that the time required to read an image signal is doubled.

In addition, a light source is required to directly illuminate the photodetector array, and a circuit is also required to control the lighting of this light source, which increases the number of parts that make up the image sensor, leading to an increase in cost. Ta.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to perform blank reading, which is performed prior to reading out an image signal by driving an image sensor, without slowing down the reading speed of the image signal and with a simple configuration. An object of the present invention is to provide an image sensor and a method for driving the same.

(Means for Solving the Problems) In order to solve the problems of the conventional example, an image sensor according to a first aspect of the present invention is characterized by having the following configuration.

A plurality of light receiving elements each having two diodes connected in series with opposite polarities are arranged in a line to form a light receiving element group.

A plurality of these light receiving element groups are provided.

A reading circuit is provided which is connected to the group common electrode of each light receiving element group.

A switch is provided for each group common electrode, which can be selectively connected to the reading circuit, bias power supply, or ground line.

A drive circuit is provided which is connected to each of the light receiving element groups in a matrix and sequentially applies a driving pulse to each of the light receiving elements constituting the light receiving element group.

The method for driving an image sensor according to a second aspect of the present invention includes dividing a light receiving element array formed by arranging in a line a plurality of light receiving elements each having two diodes connected in series with opposite polarities into a plurality of light receiving element groups; An image sensor that sequentially reads image signals of each light-receiving element constituting a light-receiving element group for each light-receiving element group by performing matrix driving is characterized by the following operation.

After reading the image signal of each light-receiving element in one light-receiving element group is completed, one end of each light-receiving element r1 in the light-receiving element group is grounded.

In this state, each light-receiving element of the next light-receiving element group is read, and at the same time, a blank reading of each light-receiving element of the first light-receiving element group is performed.

(Function) According to the invention of claim 1, since a switch is provided for the group common electrode of each light-receiving element group, which can be selectively connected to the reading circuit, the bias power supply, or the ground line, the light-receiving element group can be connected to the reading circuit. When connected to the ground line, the image signal of each photodetector can be read, when the photodetector group is connected to a bias power supply, the charges generated in the six photodetectors can be stored, and when the photodetector group is connected to the ground line, the image signal of each photodetector can be read. Empty reading can be performed.

According to the invention method of claim 2, each light receiving element group is driven in a matrix, so that at the same time when each light receiving element of a certain light receiving element group is read, each light receiving element of the light receiving element group connected to the ground line is read. Empty reading can be performed.

(Example) An image sensor according to an example of the present invention will be described with reference to FIG. In the figure, parts having the same configuration as those in FIG. 3 are designated by the same reference numerals.

The image reading part of the image sensor is a photodiode P.
The light receiving element array 2 is composed of a plurality of light receiving elements 1 arranged in a line in which a blocking diode BD and a blocking diode BD are connected in series with opposite polarities. The light-receiving element array 2 is divided into a plurality of (n) light-receiving element groups 3n each consisting of an aggregate of a plurality (64) of light-receiving elements 1.

The photodiode PD side of each light receiving element group 3n is connected to a group common electrode 8n. The group common electrode 8n is connected to an analog switch 9n.

This analog switch 9n selects connection to either the common wiring 5 connected to the integrator 4 (reading circuit), the bias power supply 6, or the ground line 10, and also selects connection to the common wiring 5. Ground wire10. Bias power supply 6. Common wiring 5. The grounding wire 10 is configured to be switched in this order. That is, the n-th light receiving element group 3n of the light receiving element groups 3n is connected to the common wiring 5 by the analog switch 9n.
, the (n-1,)th light receiving element group 3n- is connected to the grounding line 10, and all other light receiving element groups 3n are connected to the bias power supply 6.

The bias power supply 6 has its positive side connected to the group common electrode 8n so as to supply a reverse bias voltage to the blocking diode BD. This bias power supply 6 prevents charges from leaking into the group common electrode 8n of the light receiving element group 3n that is not connected to the common wiring 5, and from occurring as crosstalk (noise) when reading the first bit of the light receiving element group 3n. It is for the purpose of

The shift register SR has a 64-bit terminal, which is connected to each of the 64 light-receiving elements 1 constituting the light-receiving element group 3 by matrix wiring, and a read pulse is sequentially applied to each light-receiving element 1. It looks like this.

Next, an example of a method for driving the image sensor shown in FIG. 1 will be described with reference to a timing chart shown in FIG. 2.

Each analog switch 9n is controlled by three control pulses so that the group common electrode 8n is connected to either the common wiring 5, the bias power supply 6, or the ground line 10. That is, when the control pulse A is rHJ and the control pulses B and C are rLJ, the group common electrode 8n is connected to the integrator 4 via the common wiring 5. When control pulse B is rHJ, control pulse A and control pulse C
When is rLJ, the group common electrode 8n is connected to the ground line 10. When the control pulse C is rHJ and the pulse A and the control pulse B are "L", the group common electrode 8n is connected to the bias power supply 6.

First block photodetector group 3. When reading the image signal of each light receiving element 1, the analog switch 9 control pulse A
, the control pulse B of the final stage analog switch 9n, and the control pulse C of the other analog switches 9n are r.
HJ, which is connected to each light receiving element 1 of the light receiving element group 31 or to the integrator 4.

When a start pulse is manually applied to the shift register SR in this state, the control pulse A applied to the analog switch 91 is applied to each terminal of the shift register SR during the rHJ period.
Drive pulses (not shown) are sequentially shifted and output from .about.64.

In each light-receiving element 1, the photodiode PD is charged by scanning the immediately preceding line, and then, when the original is irradiated with light, a charge corresponding to the amount of light is discharged, and a charge corresponding to the amount of light is accumulated. In this state, when the driving pulse is sequentially applied to each light receiving element 1 of the light receiving element group 3 of the first block, the photodiode PD is recharged. Then, by reading the current flowing due to recharging via the integrator 4, each image signal is extracted in time series. At this time, due to poor switching characteristics of the blocking diode BD, recharging is not performed completely, resulting in residual charge.

Next, the light receiving element group 3 of the second block. When reading the image signal of each light receiving element, control pulse A of analog switch 9, analog switch 9. The control pulse B of , and the control pulse C of the other analog switches 90 become rHJ, and each light receiving element 1 of the light receiving element group 32 is connected to the integrator 4 .

As with the first block, driving pulses are sequentially applied by the shift register SR, and each image signal is extracted in time series from the light receiving elements 1 constituting the second block. At this time, the light receiving element group 31 of the first block is connected to the analog switch 9. It is connected to the ground wire 10 by. When driving pulses are sequentially applied to the light receiving elements constituting the second block, the driving pulses are applied to the light receiving elements n31 of the first block.
(to perform matrix drive), the light receiving element group 3. Empty reading of each light receiving element 1 is performed sequentially. Through this operation, the food diode PD is recharged again, and the residual charge is reduced. At this time, since the first block is connected to the ground line 10, it does not affect the output of the second block.

Third block photodetector group 3. When reading the image signal of each light receiving element 1, the irl l of the analog switch 9
The pulse A, the analog switch 920 control pulse B, and the control pulse C of the other analog switch 9n are r
HJ, and the light receiving element group 3. of the third block. is connected to the reading circuit 4, and the light receiving element group 3. of the second block is connected to the reading circuit 4. is to the ground wire 10,
1st block and 4th to nth blocks of light receiving element groups 3.
and the light receiving element group 3n (n=4 to n) are connected to the bias power supply 6.
The same operations as those described above are performed by connecting the two terminals to the respective terminals.

The above operation is repeated up to n blocks.

Since the recharging time is doubled by performing idle reading, the residual charge can be reduced and the performance of the image sensor can be improved.

According to the above-mentioned operation, at the same time as the reading of the light receiving element group 3n of the n block, the light receiving element group 3n- of the (n-1) block is read out.
Since + blank reading is performed, image signal reading and blank reading can be performed in one line scanning time. Furthermore, although the time in the accumulation mode is reduced by one block compared to the conventional example, since a normal image sensor is composed of a large number of blocks, sufficient time for accumulation can be secured.

(Effects of the Invention) According to the present invention, for the group common electrode of each light receiving element group,
A switch is provided that can be selectively connected to the reading circuit, bias power supply, or ground line, so when the photodetector group is connected to the reading circuit, the image signal of each photodetector can be read, and the photodetector group can be connected to the bias power supply. At times, charges generated in each light-receiving element can be accumulated, and when the light-receiving element group is connected to a ground line, blank reading of each light-receiving element can be performed.

Therefore, by driving each light-receiving element group in a matrix, reading each light-receiving element of a certain light-receiving element group is simultaneously performed, and blank reading of each light-receiving element of the light-receiving element group connected to the ground line is performed.

As a result, image signal reading and blank reading can be performed with a simple configuration and within the scanning time of one line.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram of an image sensor according to an embodiment of the present invention.
FIG. 2 is a timing chart of an example of a driving method for driving the image sensor of the embodiment shown in FIG. 1, and FIG. 3 is an equivalent circuit diagram of a conventional image sensor. 1... Light receiving element 2... Light receiving element array 3n... Light receiving element group 4... Integrator (reading circuit) 5... (Threading wire) 6...Bias power supply 7n...Block changeover switch 8n...Group common electrode 9n...Analog switch 10...Grounding line PD...Photodiode BD...Blocking diode SR...・Shift register

Claims (2)

[Claims] (1) A plurality of light receiving element groups formed by arranging a plurality of light receiving elements in a line, each consisting of two diodes connected in series with opposite polarities, and a readout element connected to a group common electrode of each of the light receiving element groups. a circuit; a switch that can be selectively connected to the reading circuit, bias power supply, or ground line for each group common electrode; and each light receiving element connected to each of the light receiving element groups in a matrix form and forming the light receiving element group. An image sensor comprising: a drive circuit that sequentially applies drive pulses to; (2) A light-receiving element array consisting of a plurality of light-receiving elements arranged in a line with two diodes connected in series with opposite polarities is divided into a plurality of light-receiving element groups, and the light-receiving element group is divided by matrix driving. In an image sensor that sequentially reads the image signals of each light-receiving element in each light-receiving element group, after reading the image signal of each light-receiving element in one light-receiving element group is completed, one end of each light-receiving element in the light-receiving element group is grounded,
A method for driving an image sensor, characterized in that, at the same time as reading each light receiving element of the next light receiving element group, blank reading of each light receiving element of the first light receiving element group is performed.