JPH0473969A - Image sensor - Google Patents

Abstract

PURPOSE:To improve an S/N ratio with a simple structure and to provide multiple gradations by forming a noise removing photodetector having the same structure as that of the photodetector, connecting one end of the noise removing photodetector to a common wiring, and connecting pulse applying means to the other end. CONSTITUTION:A noise removing photodetector 9 is disposed separately from photodetectors 1 for constituting a photodetector group 3 at one end side of a photodetector array 2. The photodetector 9 is connected in series in reverse polarity with a photodiode PD and a blocking diode BD, formed simultaneously when the array 2 is formed, and fanned in the same structure as that of the photodetector 1. The end of the photodetector 9 at the photodiode PD side is connected to a common wiring 5, and the end of the photodetector 9 at the diode BD side is connected to the head terminal of a shift register 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image sensor used in an input section of a facsimile machine, etc., and particularly relates to an image sensor that includes a plurality of light receiving elements each having two diodes connected in series with opposite polarities. The present invention relates to an improvement in an image sensor in which a light receiving element array is formed by arranging individual lines.

(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. 9, for example. It has been proposed that one light receiving element is formed and a plurality of light receiving elements are arranged in a line. In the image sensor having this structure, image signals are read out as follows.

That is, the photodiodes PD are scanned by the shift register SR, and signals are sequentially applied, and charges are accumulated in the applied photodiodes PD. Then, during one round of scanning, light is irradiated onto the photodiode PD,
Charges corresponding to the amount of light irradiated are discharged. and,
Next, a reset signal (read pulse) is sequentially applied by the shift register SR, and each photodiode PD is recharged with a charge corresponding to the amount of discharge.At this time, the electric potential generated at the output terminal Tout due to the current flowing through the loading resistor R is It is read out as a signal (for example, Japanese Patent Application Laid-open No. 5
8-62978).

The operation of one bit of the light receiving element will be explained with reference to FIG. 10. When a read pulse is applied to the blocking diode BD, the photodiode PD is reverse biased, and the capacitance Cp of the photodiode PD becomes Q-CpV.
(Here, for ease of understanding, it is assumed that there is no voltage drop due to the blocking diode BD).

Next, when the read pulse falls, the charge Q is distributed to the capacitance ratio of the capacitor Cp and the capacitor cb of the blocking diode BD. At this time, distribution is performed via the loading resistor R, so -QX Cb / (Cp +
Cb) is detected as the output.

Therefore, at the falling edge of the read pulse, -
Switching noise of QxCb/(Cp+Cb) is generated.

Next, light enters the photodiode PD within a certain period of time,
If a charge of Δq is generated and distributed between the capacitor Cp and the capacitor cb, the charge stored in the capacitor Cp is (Q-Δq
)xCp/(Cp+Cb). When the pulse is applied again, the charge of Q is accumulated in the capacitor Cp again, so Q-(Q-ΔQ)xCp/(Cp+Cb)=Q
xCb/(Cp+Cb)+ΔqXCp/(Cp+Cb
) is detected as an output signal (FIG. 11).

(Problems to be Solved by the Invention) According to the readout method of the image sensor described above, as shown in FIG.
) and the noise component QxCb/(Cp+cb) are output together. Therefore, in order to obtain the final read signal, it was necessary to separate the read signal and noise.

In the method disclosed in Japanese Patent Application Laid-open No. 58-62978,
An integrator is inserted at the position of the loading resistor R in FIG. 9, and this integrator is used to integrate the entire period from the rise to the fall of the read pulse, thereby removing noise components and outputting an image signal.

In addition, 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 array, and this light receiving element array is formed into a plurality of light receiving element groups consisting of a collection of light receiving elements. An image sensor has been proposed in which the light-receiving element groups are sequentially selected by driving the light-receiving element groups in matrix and connected to a reading circuit to read the signal of each light-receiving element.

By switching the matrix drive switch, first, noise at the fall of the read pulse is not input to the read circuit, and an output that is a mixture of the image signal component and the noise component when the read pulse rises. A method is adopted in which only the image signal is extracted by separately integrating the output of only the noise component and differentially amplifying these two outputs (for example, IEICE Transactions Vol. 1. J 69-C No. 11).
"Two-dimensional optical sensor using ra-8i diode")
.

However, according to the above reading method, the noise component is larger than the image signal component, so the amplifier and integrator must be designed so that they do not saturate even if the noise component is input, and the image signal is output with a small dynamic range. Therefore, there is a problem that the SZN ratio becomes about 10 to 20 dB.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a structure of an image sensor that can eliminate noise components with a simple configuration, improve the S/N ratio, and achieve multi-gradation. .

(Means for Solving the Problems) In order to solve the problems of the conventional example described above, the image sensor of the present invention receives light by arranging a plurality of light receiving elements in a line in which two diodes are connected in series with opposite polarities. In an image sensor that forms an element array, connects one end of each of the light-receiving elements to a common wiring connected to a reading circuit, and reads an image signal by sequentially applying a readout pulse to the other end of each light-receiving element. It is characterized by its composition.

That is, a noise-removing light-receiving element having the same structure as the light-receiving element is formed separately from the light-receiving element constituting the light-receiving element array. Then, one end of the noise removing light receiving element is connected to the common wiring. Further, a pulse applying means is connected to the other end of the noise removing light receiving element.

(Function) According to the present invention, when a pulse is applied to the noise-eliminating light-receiving element at a desired timing, switching noise generated when applying a read pulse to the light-receiving element of the light-receiving element array is canceled out. I can do it.

(Example) An image sensor according to an example of the present invention will be described with reference to FIG.

This image sensor is of a matrix driving type using one shift register in order to reduce the number of drive fcs.

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 (63) of light-receiving elements 1.

The photodiode FD side of each light receiving element group 3n is connected to a block selection switch 7 that selects connection to a common wiring 5 connected to an integrator 4 (reading circuit) or a bias power supply 6. The bias power supply 6 is for preventing crosstalk from occurring within the light receiving element group 3n. Further, the common wiring 5 at the input section of the integrator 4 can be grounded via an analog switch 8.

At one end of the light-receiving element array 2, a noise-removing light-receiving element 9 is arranged, in addition to the light-receiving elements 1 constituting the light-receiving element group 3. This noise-eliminating light-receiving element 9 is formed by connecting a photodiode PD and a blocking diode BD in series with opposite polarities, and is formed at the same time when forming the light-receiving element array 2. It is designed to have the same structure as 1.

The photodiode PD side end of the noise removing light receiving element 9 is connected to the common wiring 5, and the blocking diode BD side end of the noise removing light receiving element 9 is connected to the leading terminal of the shift register 10.

The shift register 10 has 64-bit terminals, and the 2nd to 64th terminals are connected to each of the 63 light-receiving elements 1 constituting the light-receiving element group 3 by matrix wiring, and a readout pulse is sent to each light-receiving element 1. are applied sequentially.

The specific structure of the light receiving element 1 is, as shown in FIG. 2, a transparent substrate 21 made of glass or the like and a metal electrode 22 made of chromium or the like. p10a-3i; H layer 23a, i a-9
i; A photoelectric conversion layer 23 consisting of an H layer 23b and an n''a-S i HH layer 23c. A transparent electrode 24 made of indium tin oxide, etc.; an insulating layer 25 made of polyimide etc. is sequentially laminated and patterned to block the photodiode PD. A diode BD is formed, and lead wiring lines 27a and 27b made of chromium or the like are formed through contact holes 26.26 formed in the insulating layer 25.Photodiode P
On the D side, a light receiving area A is formed which is irradiated with light from above, and the blocking diode BD side is shielded from light by an extraction wiring 27b so as not to be irradiated with light.

Further, as shown in FIG. 3, two diodes may be formed by a photodiode PDI and a photodiode PD2, and the photodiode PD2 may have the function of a blocking diode. According to the structure shown in FIG. 3, by connecting two photodiodes with opposite polarities, the voltages generated when light is irradiated are made equal, and current does not flow to the outside.

In FIGS. 2 and 3, the photoelectric conversion layer 23 is
Although an example is given in which a diode is used, a Schottky electrode/i/n or the like may be used, or a single crystal silicon, polysilicon, or the like may be used.

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. 4.

The connection between the light-receiving element group 3n and the integrator 4 is performed by sequentially shifting the block changeover switch 7n. That is,
When a pulse of rHJ is applied to the block changeover switch 7n, each light receiving element group 3n is connected to the integrator 4, and when a pulse of rLJ is applied to the block changeover switch 7n, the light receiving element group 3n is connected to the bias power supply 6. Connected. Therefore, one block of the plurality of light receiving element groups 3 is connected to the integrator 4.
, the other light receiving element groups 3 are connected to the bias power supply 6.

When a start pulse is manually applied to the shift register 10,
The control pulse applied to the block changeover switch 7 is
During the HJ period, read pulses are sequentially shifted and output from each terminal 1 to 64 of the shift register 10. Then, the readout pulse is transmitted to the noise removing light receiving element 9 and the first
Photo-receiving element group of block 3. Each image signal is extracted in time series by reading the current that flows through the integrator 4 by sequentially applying a current to each light receiving element 1 and recharging it. Further, the read pulses from each terminal of the shift register 10 are performed at timings such that the falling edge and the rising edge coincide.

The analog switch 8 is connected to the block changeover switch during the period from the second half of the read pulse at the last terminal (64th) of the shift register 10 to the first half of the read pulse at the first terminal of the shift register 10 that drives the next block. 7n), a control pulse of rHJ is applied, and the analog switch 8 is closed to ground the input section of the integrator 4.

Therefore, when the first read pulse of the shift register 10 rises, the analog switch 8 is closed and the integrator 4
Since the input section of the integrator 4 (readout circuit) is grounded, switching noise generated by the rising edge of the first readout pulse is not input to the integrator 4 (readout circuit) side.

The switching noise generated by the falling edge of the first read pulse can be canceled out by being canceled out by the switching noise generated by the rising edge of the second read pulse. Similarly, the switching noise generated at the falling edge of the 63rd read pulse is canceled by the switching noise generated at the rising edge of the next read pulse.

At the falling edge of the 64th read pulse, the analog switch 8 is closed and the input part of the integrator 4 is grounded, so switching noise generated by the falling edge of the 64th read pulse is absorbed by the integrator 4 (reading circuit). Not entered on the side. The image signal of the 63rd light receiving element 1 of the 1st block light receiving element group 3 is read by the 64th readout pulse, but as shown in FIG. 11(b), the image signal is at the rising edge of the readout pulse. Therefore, there is no problem even if the common wiring 5 is grounded in the latter half of the 64th read pulse. In addition, the common wiring 5 is also grounded at the rising edge of the first read pulse, but since the first read pulse is for driving the noise removal light receiving element 9, there is no need to read this signal accurately. .

At the time of block switching, since the input part of the integrator 4 is grounded, the charge accumulated in the photodetector 1 of each photodetector group 3n is discharged by applying the bias power supply 6 before connecting to the common wiring 5. This prevents the generation of noise.

Another example of the method for driving the image sensor shown in FIG. 1 will be described with reference to the timing chart shown in FIG. 5.

The connection between the light-receiving element group 3n and the integrator 4 is performed by sequentially shifting the block changeover switch 7n in the same manner as in the above-described driving method. In other words, r to the block changeover switch 7n.
When the HJ pulse is applied, each light receiving element group 3n is connected to the integrator 4, and the block changeover switch 7n is connected to rLJ.
When the pulse is applied, each light receiving element group 3n is connected to the bias power supply 6. Therefore, when one block of the light receiving element group 3n is connected to the integrator 4, the other light receiving element group 3 is connected to the bias power supply 6.

When a start pulse is input to the shift register 10,
Read pulses are sequentially shifted and output from each terminal 1 to 64 of the shift register 10.

The first read pulse of the shift register 10 is applied before the control pulse applied to the block changeover switch 7. When the control pulse applied to the block changeover switch 71 is applied to the light receiving element group 3 of the first block during the rHJ period, Each image signal is extracted in time series by reading the current that flows through the integrator 4 by sequentially applying a current to each light receiving element 1 and recharging it. Further, the read pulses from each terminal of the shift register 10 are performed at timings such that the falling edge and the rising edge coincide. Furthermore, the timing of the fall of the read pulse of the 64th bit of the light receiving element group 3 of the n block and the rise of the read pulse of the 1st bit of the light receiving element group 3 of the (n+1) block are made to coincide.

An rHJ pulse is applied to the analog switch 8 when the block changeover switch 7n is switched, and the analog switch 8 is closed to ground the input section of the integrator 4.

Therefore, the switching noise generated by the rising edge of the first read pulse of the shift register 10 can be canceled out by being canceled out by the switching noise generated by the falling edge of the 64th read pulse of the previous block.

The switching noise generated by the falling edge of the first read pulse can be canceled out by being canceled out by the switching noise generated by the rising edge of the second read pulse. The same process is repeated thereafter, and the switching noise generated at the falling edge of the read pulse is canceled by the switching noise generated at the rising edge of the next read pulse.

When switching the light receiving element group 3 connected to the integrator 4, the integrator 4 is switched by closing the analog switch 8.
The human power section of the light receiving element 1 is grounded, and the charge accumulated in each light receiving element 1 is discharged by a bias power supply 6 before being connected to the common wiring 5, thereby preventing the generation of noise.

In the above embodiment, it is not necessary for the falling and rising edges of the pulse to cancel out switching noise to perfectly match, and even if they deviate by about 10 to 20 ns, the response speed of the integrator etc. is slow, so the reading output will be affected. do not.

If the image sensor shown in FIG. 1 is driven according to the timing charts shown in FIGS. 4 and 5, noise components can be removed and accurate image signals can be obtained.

Moreover, since switching noise can be eliminated by connecting the noise-removing light-receiving element 9 to the leading terminal of the shift register, there is no need to provide special means for applying pulses to the noise-removing light-receiving element 9.

Sixth image sensor according to another embodiment of the present invention
This will be explained with reference to the figures.

This image sensor is driven by a driving I as in the embodiment shown in FIG.
In order to reduce the number of C's, a single shift register is used for matrix driving.

The difference between this embodiment and the image sensor of the embodiment shown in FIG. 1 is that the noise removal light receiving element 9 of the embodiment of FIG. The noise removing light receiving element 9 has a blocking diode BD side end connected to the pulse generator 11.

The shift register 10 has 64-bit terminals, and the 1st to 64th terminals are the 64-bit terminals that constitute the light receiving element group 3.
It is connected to each of the four light receiving elements 1 by matrix wiring, so that a read pulse is sequentially applied to each light receiving element 1.

Since the other configurations are the same as those of the embodiment shown in FIG. 1, the same reference numerals are given and the explanation will be omitted.

Next, an example of a method for driving the image sensor shown in FIG. 6 will be described with reference to a timing chart shown in FIG. 7.

The connection between the light receiving element group 3 and the integrator 4 is performed by sequentially shifting the block changeover switch 7n.

That is, when a pulse of rHJ is applied to the block changeover switch 7n, each light receiving element group 3n is connected to the integrator 4, and when a pulse of "L" is applied to the block changeover switch 7n, the light receiving element group 3n is connected to the integrator 4. Connected to bias power supply 6. Therefore, when one block among the plurality of light receiving element groups 3 is connected to the integrator 4, the other light receiving element groups 3 are connected to the bias power supply 6.

When a start pulse is input to the shift register 10,
The control pulse applied to the block changeover switch 7 is
During the HJ period, read pulses are sequentially shifted and output from each terminal 1 to 64 of the shift register 10. This readout pulse is sequentially applied to each light receiving element 1 of the light receiving element group 31 of the first block, and each image signal is extracted in time series by reading the current flowing by recharging through the integrator 4. do. In addition, shift register 10
The read pulses from each terminal are performed at timings such that the falling and rising edges coincide.

A block changeover switch 7 is connected to the noise removal light receiving element 9.
A noise-eliminating light-receiving element drive pulse is applied that rises when switching n and falls when the read pulse of the leading terminal of the shift register 10 rises.

An rHJ pulse is applied to the analog switch 8 when the block changeover switch 7n is switched, and the analog switch 8 is closed to ground the input section of the integrator 4.

Therefore, the switching noise generated by the rising edge of the first read pulse of the shift register 10 can be canceled out by being canceled out by the switching noise generated by the falling edge of the noise-eliminating light-receiving element driving pulse. The switching noise generated by the falling edge of the first read pulse can be canceled out by being canceled out by the switching noise generated by the rising edge of the second read pulse. Similarly, the switching noise generated at the falling edge of the 63rd read pulse is canceled by the switching noise generated at the rising edge of the next read pulse.

Furthermore, at the falling edge of the readout pulse for the final bit (64th) of each block, the analog switch 8 is closed and the input part of the integrator 4 is grounded. Noise is not input to the integrator 4 (reading circuit) side.

At the time of block switching, since the input part of the integrator 4 is grounded, the charge accumulated in the photodetector 1 of each photodetector group 3 is discharged by applying the bias power supply 6 before connecting to the common wiring 5. This prevents the generation of noise.

Another example of the method for driving the image sensor shown in FIG. 6 will be described with reference to the timing chart shown in FIG. 8.

The connection between the light-receiving element group 3n and the integrator 4 is performed by sequentially shifting the block changeover switch 7n in the same manner as the driving method shown in FIG. That is, when the rHJ pulse is applied to the block changeover switch 7n, each light receiving element group 3n is connected to the integrator 4, and the block changeover switch 7n
When a pulse of rLJ is applied to each light receiving element group 3n
is connected to the bias power supply 6. Therefore, the light receiving element group 3
When one block of n is connected to integrator 4,
The other light receiving element groups 3n are connected to the bias power supply 6.

When a start pulse is manually applied to the shift register 10,
The control pulse applied to the block changeover switch 7 is
During the HJ period, read pulses are sequentially shifted and output from each terminal 1 to 64 of the shift register 10. This readout pulse is transmitted to the light receiving element group 3 of the first block. Each image signal is extracted in time series by reading the current that flows through the integrator 4 by sequentially applying a current to each light receiving element 1 and recharging it. In addition, shift register 10
The read pulses from each terminal are performed at timings such that the falling and rising edges coincide.

A noise-eliminating light-receiving element drive pulse is applied to the noise-eliminating light-receiving element 9, which rises at the falling edge of the readout pulse at the final terminal (64) of the shift register 10 and falls at the rising edge of the readout pulse at the leading terminal of the shift register 10. It is now possible to do so.

The analog switch 8 receives r from the noise removal light receiving element drive pulse when switching the block changeover switch.
A control pulse having a short pulse width during the HJ period is applied, and the analog switch 8 is closed to ground the input section of the integrator 4.

Therefore, the switching noise generated by the rising edge of the first read pulse of the shift register 10 can be canceled out by being canceled out by the switching noise generated by the falling edge of the noise-eliminating light-receiving element driving pulse. The switching noise generated by the falling edge of the first read pulse can be canceled out by being canceled out by the switching noise generated by the rising edge of the second read pulse. Similarly, the switching noise generated at the falling edge of the 63rd read pulse is canceled by the switching noise generated at the rising edge of the next read pulse.

Moreover, the switching noise generated by the falling edge of the read pulse of the final bit (64th) of each block can be canceled out by being canceled out by the switching noise generated by the rising edge of the noise-eliminating light-receiving element driving pulse.

At the time of block switching, since the input part of the integrator 4 is grounded, the charge accumulated in the photodetector 1 of each photodetector group 3 is discharged by applying the bias power supply 6 before connecting to the common wiring 5. This prevents the generation of noise.

If the image sensor shown in FIG. 6 is driven according to the timing charts shown in FIGS. 7 and 8, noise components can be removed and accurate image signals can be obtained.

Furthermore, since the signal read through the integrator 4 does not include the output component from the noise removal light receiving element 9, the image signal processing circuit connected to the output side of the integrator 4 can be simplified. .

According to the image sensor described above (Figs. 1 and 6), the S/N ratio is reduced to 30 to 40 dB by removing noise components.
To some extent, it is possible to enable high gradation reading of the image sensor. Moreover, since the newly provided noise-removing light-receiving element 9 has the same structure as the other light-receiving elements 1, it can be easily manufactured without increasing the number of manufacturing steps.

Although the image sensors described above (FIGS. 1 and 6) are based on the matrix drive method, they may also be applied to the line-sequential drive method shown in FIG. 9. In other words, the switching noise generated at the rising edge of the read pulse applied to the light receiving element of the first bit and the switching noise generated at the falling edge of the read pulse applied to the light receiving element of the last bit are removed. This is done by applying a pulse to the light-receiving element. Further, in this case, since there is no need for switching, there is no need to consider noise generated between blocks.

(Effects of the Invention) According to the present invention, a noise-removing light-receiving element is provided separately from the light-receiving element array, and when a pulse is applied to the noise-eliminating light-receiving element at a desired timing, a readout pulse is sent to the light-receiving element of the light-receiving element array. It is possible to eliminate switching noise that occurs when applying , improve the S/N ratio of the image sensor, and achieve multi-gradation.

[Brief explanation of drawings]

FIG. 1 is an equivalent circuit diagram of an image sensor according to an embodiment of the present invention.
2 and 3 are cross-sectional explanatory diagrams of the light receiving element of the image sensor of FIG. 1, and FIG. 4 is a timing chart of an example of a driving method for driving the image sensor of the embodiment of FIG. 1.
5 is a timing chart of another example of the driving method for driving the image sensor of the embodiment shown in FIG. 1, FIG. 6 is an equivalent circuit diagram of an image sensor according to another embodiment of the present invention, and FIG. 6 is a timing chart of an example of a driving method for driving the image sensor of the embodiment shown in FIG. 6, FIG. 8 is a timing chart of another example of a driving method of driving the image sensor of the embodiment of FIG. Figure 9 is an equivalent circuit diagram of a conventional image sensor, Figure 10 is an equivalent circuit diagram of a 1-bit light-receiving element, Figure 11 (a) is a diagram showing the output waveform when focusing on a 1-bit light-receiving element, and Figure 11. FIG. (b) Readout pulse... Light receiving element 2... Light receiving element array 3n... Light receiving element group 4... Integrator (reading circuit) 5... Common wiring 6...Bias power supply 7n...Block changeover switch 8...Analog switch 9...Noise removal light receiving element 10...Shift register 11... ...Pulse generator PD ... Photodiode BD ... Blocking diode Fig. 9 Fig. 11 Readout pulse

Claims (1)

[Claims] 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 array, and one end of each light receiving element is connected to a common wiring connected to a reading circuit, In an image sensor that sequentially applies a readout pulse to the other end of each light receiving element to read an image signal, a noise removing light receiving element having the same structure as the light receiving element is formed separately from the light receiving element constituting the light receiving element array. An image sensor characterized in that one end of a noise-removing light-receiving element is connected to the common wiring, and a pulse applying means is connected to the other end of the noise-removing light-receiving element.