JPH05276380A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To provide the solid-state image pickup device able to correct a bias light signal component in real time in the solid-state image pickup device to which the bias light is emitted to improve the response of a sensor. CONSTITUTION:A bias light signal output from a bias light photoelectric conversion element 15 and a signal output from a photoelectric conversion element 12 are given to a drive circuit 19, from which a time series signal of one line is outputted, the bias light signal output is sampled by a latch circuit and the signal output is corrected through differential compensation between the signal outputs, then the bias light signal output is sampled for each line for differential compensation, then the bias light signal component is corrected in real time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device used for an image input device such as a facsimile machine and a copying machine, and more particularly to improving the photoresponsiveness of a photoelectric conversion element formed on a transparent insulating substrate. The present invention relates to improvement of a solid-state imaging device having a structure in which a photoelectric conversion element is irradiated with bias light.

[0002]

2. Description of the Related Art In recent years, in solid-state image pickup devices used for image input devices such as facsimiles and copying machines, it has been desired to increase the reading speed. The solid-state image pickup device uses, for example, an electrical scanning (main scanning) by a long contact image sensor having a width substantially equal to the document width, and a relative movement (sub-scanning) between the sensor and the document surface by the document feeding means. The image of the entire surface is read line-by-line in a time-series manner, and as an important factor related to increasing the reading speed, it corresponds to the brightness of the optical signal when the reflected light from the document surface is received by the photoelectric conversion element. The reactivity (light responsiveness) can be mentioned. By improving this optical response, the afterimage of the sensor output (a phenomenon in which some of the signals on the previous line remain on the next line) is reduced, and the drive frequency for reading in time series is increased to speed up the process. Can be planned.

Conventionally, as a means for improving the photoresponsiveness in a solid-state image pickup device, a structure has been proposed in which a photoelectric conversion element is constantly irradiated with bias light. That is, for example, as shown in FIG. 9, a-Si, CdS is formed on the insulating substrate 90.
A document illumination light source 92 and a bias illumination light source 93 are provided for an image sensor 91 formed by forming a plurality of thin film photoelectric conversion elements such as -CdSe in a line shape, and the light from the document illumination light source 92 is reflected on the document surface. Imaging lens 9 reflected by 94
The light from the bias illumination light source 93 is guided to the image sensor 91 via the light source 5 and directly illuminates the image sensor 91 (see, for example, JP-A-62-62).
-204657 and JP-A-2-234563). According to the above device, by irradiating the bias light, traps in the thin film photoelectric conversion layer forming the photoelectric conversion element can be reduced, and the photoresponsiveness can be improved.

In the case of the solid-state image pickup device having the above structure,
Since the reflected light from the document surface 94 and the bias light are simultaneously incident on the image sensor 91, in order to obtain the signal corresponding to the document image information, the bias signals are output from the photoelectric conversion elements of the image sensor 91. It is necessary to take a signal correction means for removing the bias optical signal component generated by light. That is, first, the original illumination light source 92 is turned off and only the bias illumination light source 93 is turned on before reading the original image information. In this state, the bias optical signal component data obtained by performing the reading operation by the image sensor 91 is converted into a digital signal and stored in a memory element or the like for each line or each area. afterwards,
The original illumination light source 92 is turned on, the reflected light from the original and the bias light are made incident on the image sensor 91, the signal data obtained by performing the reading operation is converted into a digital signal, and is converted into a memory element or the like in units of lines or areas. Remember. Then, by performing an operation for removing the bias light signal component data from this signal data, it is possible to obtain the image signal component of only the document information.

[0005]

However, the solid-state image pickup device as described above has the following problems. Since the bias optical signal component is corrected in the digital signal state, 30 of the resolution levels of the A / D converter are used.
% Is taken as the bias light signal component, the resolution level assigned to the document reflected light component is reduced, and the gradation reproducibility of the document image signal is deteriorated. Especially, in the case of a color image reading apparatus which requires high gradation reproducibility, the above influence is greatly exerted. Further, since only the light source for bias illumination is turned on and the bias light signal component of one line read by the first scanning of the image sensor is used for correction of each line thereafter, it is possible to avoid the lapse of time due to flicker or noise of the light source for bias illumination. There is a deviation in the correction amount for each line due to the change in the target light amount, and it is difficult to perform accurate correction. Furthermore, providing a memory element for each line or area is
This imposes a heavy cost burden on the solid-state imaging device and raises its price.

The present invention has been made in view of the above circumstances, and in a solid-state image pickup device for irradiating a photoelectric conversion element with bias light, a solid-state image pickup device capable of correcting a bias light signal component in real time with an inexpensive and simple structure. Is intended to provide.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, the present invention provides a photoelectric conversion element formed on a transparent insulating substrate for receiving the reflected light from the original surface, and the photoelectric conversion element. A solid-state imaging device having a light source unit for irradiating a bias light, is characterized by having the following configuration. A bias light photoelectric conversion element that shields the reflected light and receives only the bias light is formed near the photoelectric conversion element. A drive circuit is provided which outputs the bias light signal output from the bias light photoelectric conversion element and the reflected light signal output from the photoelectric conversion element in a time series order. A holding circuit is provided for sampling each signal separately. Differential compensation means is provided for outputting the difference between the held reflected light signal output and the bias light signal output.

[0008]

According to the present invention, the bias optical signal output from the bias light photoelectric conversion element and the reflected optical signal output from the photoelectric conversion element are output in time series with the bias optical signal at the head. .. Each output signal is separately sampled by the holding circuit. The held output signals are input to the differential compensation means, and the difference between the two signals is output in the differential compensation means. Therefore, since the bias optical signal output is sampled for each line and differential compensation is performed, the bias optical signal component in the reflected optical signal can be corrected in real time.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the solid-state image pickup device according to the present invention will be described with reference to FIGS. FIG. 1 is a plan view of the solid-state imaging device, and FIG. 2 is a cross-sectional view taken along the line AA ′ of FIG. A plurality of photoelectric conversion elements 12 are arranged in a line in a line on an insulating transparent substrate 11 made of glass or the like to form a sensor array 13. By covering the several (four in the case of FIG. 2) photoelectric conversion elements 12 located on one end side of the sensor array 13 with the light-shielding film 14 which is common to each element, light is emitted from above. Bias light photoelectric conversion element 15 having a structure that does not enter
Is formed. If one bias light photoelectric conversion element 15 is provided, the output of the bias light component can be obtained.
By providing a plurality of these and calculating an average value for 1 bit by a circuit described later, it is possible to remove the variations in the element specific, and to correct the bias light component more accurately. You can

The structure of the photoelectric conversion element 12 will be described with reference to FIGS. 3A and 3B showing the structure of one pixel. The bias light photoelectric conversion element 15 is the same as the photoelectric conversion element 12 except for the configuration in which the light shielding film 14 is formed on the upper portion. A plurality of rectangular metal electrodes 12a made of chrome and discretely formed for each pixel in the front-back direction of the figure; two photoelectric conversion layers 12b made of hydrogenated amorphous silicon formed in a strip shape in the front-back direction of the figure;
The transparent electrode 12c made of indium tin oxide or the like and covering the metal electrode 12a for each pixel is provided with an insulating transparent substrate 11
A photoelectric conversion element 12 composed of a photodiode PD and a blocking diode BD having a thin film sandwich structure is formed by sequentially stacking and patterning the layers.
The photodiode PD and the blocking diode BD are connected in series in a state where their polarities are opposite to each other by using a common metal electrode 12a on the cathode side. The photodiode PD and the blocking diode BD are covered with an insulating layer 20 made of polyimide or the like, and contact holes 21 and 22 are formed in the insulating layer 20. Transparent electrode 12c on the side of the photodiode PD
Is a photoelectric conversion element 12 and a bias light photoelectric conversion element 1
The transparent electrode 12c on the blocking diode BD side is connected to the drive signal line 24 for each pixel. A protective film 25 is coated on the photodiode PD and the blocking diode BD, and a light incident region 26 is formed so that the reflected light from the document enters the photodiode PD and the blocking diode BD.

A plurality of driving ICs 16 are mounted on the insulating transparent substrate 11 on which the photoelectric conversion elements 12 and the bias light photoelectric conversion elements 15 are formed in a line.
The drive signal lines 24 are connected to the pads 16a. The transparent insulating substrate 11 is mounted on a support plate 10 which also serves as a wiring substrate and is made of ceramics, glass epoxy resin or the like, and on the support plate 10, solid-state LED light sources are arranged in an array to form a light source for bias illumination. Three
0 is arranged along the side surface of the transparent insulating substrate 11. Light from the bias illumination light source 30 enters the insulating transparent substrate 11 by entering from the side surface of the insulating transparent substrate 11.
Total reflection is repeated in the inside, and uniform light is given to the metal substrate 12a side which is the back side of the photoelectric conversion element 12 and the bias light photoelectric conversion element 15 by the light scattering effect. Photoelectric conversion element 12
In the photoelectric conversion layer 1 due to the incidence of the bias light.
The traps in 2b are reduced to improve the photoresponsiveness. Further, an equal-magnification imaging lens 31 is arranged above the photoelectric conversion element 12 and the bias light photoelectric conversion element 15, and a document illumination light source arranged along the photoelectric conversion element 12 and the bias light photoelectric conversion element 15. The light from 32 is the original surface 3
It is reflected at 3, and is guided through the same-magnification imaging lens 31. Therefore, the bias light enters the photoelectric conversion element 12 and the bias light photoelectric conversion element 15 from the back surface thereof, and the original surface 33 of the original surface 33 enters the photoelectric conversion element 12 from above.
The reflected light from is incident.

The photoelectric conversion elements 12 and the bias light photoelectric conversion elements 15 are differentially compensated on the support substrate 10 from the output terminals 23a at the ends of the signal reading lines 23 via the bonding wires 17. It is connected to the circuit 18. The differential compensation circuit 18 and the driving IC 16 located at the end of the insulating transparent substrate 11 are connected to a driving circuit 19 installed outside. In this drive circuit 19,
Driving IC 1 for starting scanning of one line shown in FIG.
6, a start pulse signal 61 to be applied to 6, a drive pulse 62 for reading the signals of each photoelectric conversion element 12 and the bias light photoelectric conversion element 15, and sampling pulses 64 and 65 to be applied to the differential compensation circuit 18, respectively. Feeding the circuit. Further, the driving ICs 16 are connected to each other, and the driving ICs 16 of the next stage are sequentially operated in response to the driving completion signal of the driving ICs 16 of the preceding stage.

Next, the circuit configuration of the differential compensation circuit 18 will be described with reference to FIG. The differential compensation circuit 18 is
A current amplification amplifier 51, an output of the amplifier 51 is divided into two systems, an arithmetic circuit 52 connected to one of them, a sample hold circuit 53 connected to the arithmetic circuit 52, and an output of the current amplification amplifier 51. Sample and hold circuit 54 connected to another system of
It is composed of a differential amplification amplifier 55 which receives the outputs of 3, 54 as inputs. The arithmetic circuit 52 uses the photoelectric conversion elements 15 for bias light among the outputs from the current amplification amplifier 51.
After selecting and integrating the bias light signals from the above, the bias light signals are divided by the number of the bias light photoelectric conversion elements 15 to calculate and output the average value. Each sample hold circuit 5
Reference numerals 3 and 54 are composed of a charge storage capacitor C and a transistor T which is rendered conductive by a sampling pulse 64 or a sampling pulse 65. In the sample hold circuit 53, the sampling pulse 65 which becomes “H level” in correspondence with the driving of the photoelectric conversion element 12.
Thus, the signal from the photoelectric conversion element 12 is held. Also,
In the sample hold circuit 53, the signal from the bias light photoelectric conversion element 15 is held by the sampling pulse 64 which becomes “H level” when the bias light photoelectric conversion element 15 is driven. Amplifier 55 for differential amplification
Outputs the difference between the voltage values output from the sample hold circuits 53 and 54.

The document reading operation of the solid-state image pickup device will be described with reference to FIGS. 1, 4, 5, and 6. By turning on the original illumination light source 32 and the bias illumination light source 30, the photoelectric conversion element 12 receives reflected light from the original surface 33 from above and bias light from below, and the photoelectric conversion element 15 for bias light has a light-shielding film. Since 14 is formed, only bias light enters from below. On the other hand, the start pulse 61 from the drive circuit 19 causes the drive IC 16
Applied to each pad 16 of the driving IC 16
Pulses are sequentially shifted and output from the right side to the left side of a, and each photodiode P of the sensor array 13 including the photoelectric conversion element 12 and the bias light photoelectric conversion element 15 is output.
The charge is accumulated in D by the voltage application by the drive pulse 62, and the reset state is established. In this state, the photoelectric conversion element 1
When the reflected light including the original image information and the bias light are irradiated on the light source 2, the accumulated charges are discharged according to the amount of incident light, and the accumulated charges are discharged by the bias light in the bias light photoelectric conversion element 15.

In this state, drive pulses 62 from the drive IC 16 to the blocking diode BD side of the photoelectric conversion element 12 and the bias light photoelectric conversion element 15 via the drive signal lines 24 are arranged in this order from the right side to the left side in the drawing. When applied to the element, each photoelectric conversion element 12 is charged according to the amount of discharge, so that a current flows through the read signal line 23. This operation is performed for each element, and the differential compensation circuit 18 is provided with a time-series signal 63 with the bias optical signal at the head.
Is entered. The current that flows is the amplifier 51 for current amplification.
The signal is amplified by, and divided into two systems and input to the arithmetic circuit 52 and the sample hold circuit 54, respectively. In the arithmetic circuit 52, only the first few bits (four in this embodiment) of the bias optical signal output of the time series signal are fetched,
After integrating these, an average value for 1 bit is calculated and output. This bias light signal average value is input to the sample hold circuit 53, and the sampling pulse 64 from the drive circuit 19 is applied to the gate of the transistor, so that a current corresponding to the bias light component average value is passed through the capacitor C. , As the bias optical signal voltage. Further, in the sample hold circuit 54,
By applying the sampling pulse 65 from the drive circuit 19 to the gate of the transistor T, a current containing a bias light component corresponding to the reflected light signal from the photoelectric conversion element 12 is passed through the capacitor C and held as an actual signal voltage. To do. In the differential compensation circuit 55, the voltage from each capacitor C is input, and the difference between both voltages is output to output the image signal 66 corresponding to the net image information signal obtained by subtracting the bias signal voltage from the actual signal voltage. .. This image signal is digitally processed by an A / D converter (not shown) connected to the subsequent stage of the differential compensation circuit 55.

According to this embodiment, since the bias optical signal component is corrected before conversion into a digital signal, A / A
All the resolution levels of the D converter can be assigned to the reflected light components of the original, and the resolution levels can be increased to improve the gradation reproducibility of the original image signal. Even if the amount of bias light from the bias illumination light source 30 changes, the bias light signal component obtained by the bias light photoelectric conversion element 15 is held in the sample hold circuit 53 for each line of the reading cycle, and photoelectric conversion is performed. Since the output of the conversion element 12 is corrected, an image signal faithful to the original image information can be obtained for each line.

FIGS. 7 and 8 show an example in which the present invention is applied to a matrix drive type solid-state image pickup device capable of reading a color image. In the figure, parts having the same configurations as those in FIGS. 1 and 2 are denoted by reference numerals. Hereinafter, a description will be given focusing on the parts different in configuration from the embodiment of FIGS. 1 and 2. In the solid-state imaging device of this embodiment, the sensor array 13 is divided into a plurality of blocks, the photoelectric conversion elements 12 in each block are connected to each driving IC 16 (SR1 to SR4), and each driving IC 16 is driven by a driving circuit. The driving is performed by the matrix method of selectively operating 19. In the case of matrix driving, the photoelectric conversion elements 12 and the bias light photoelectric conversion elements 15 are arranged in a line as in the first embodiment, and the bias light photoelectric conversion elements 15 are arranged at the ends of the sensor array of each block. Then, since there is an unreadable portion as the one-dimensional sensor, as shown in FIG. 7, several (two in the figure) bias light photoelectric conversion elements 1 are provided in each block.
5 is arranged two-dimensionally by being shifted in the sub-scanning direction with respect to the photoelectric conversion element 12. The connection between the bias light photoelectric conversion element 15 and the photoelectric conversion element 12 and the driving IC 16 is the first
Similar to the embodiment, the bias light photoelectric conversion element 15 and the photoelectric conversion element 12 are connected in this order so that signals can be read in time series. Specifically, the photoelectric conversion element 12 at the right end of each block is connected to the third and subsequent bits from the right side of each driving IC 16, and the photoelectric conversion element for bias light is displaced from the photoelectric conversion element 12 at the right end in the sub-scanning direction. The element 15 is connected to the second bit of the driving IC 16 by the driving signal line 24a. In addition, the photoelectric conversion element 12 of the second bit from the right
On the other hand, the bias light photoelectric conversion element 15 deviated in the sub-scanning direction is connected to the right end bit of the driving IC 16 by a drive signal line 24b arranged outside the block of the drive signal line 24a. The common signal line 27 of each block is connected to the read signal line 23 via the analog multiplexer 23b, and the common signal line 27 of one block is selectively connected to the read signal line 23 under the control of the analog multiplexer 23b. I am configuring. Further, by arranging R (red), G (green), and B (blue) filters 40 on the photoelectric conversion element 12 periodically, a color image can be read.

According to this embodiment, the bias signal component is first read from the bias light photoelectric conversion element 15 for each block, and differential compensation is performed by the differential compensation circuit 18 as in the first embodiment. The output of the photoelectric conversion element 12 can be corrected by sampling the bias signal component every time, and an image signal faithful to the original image information can be obtained for each block.

In each of the above-mentioned embodiments, the photoelectric conversion element 12 and the bias light photoelectric conversion element 15 are constituted by the sensor in which two photodiodes are arranged so as to face each other. However, charges corresponding to the reflected light from the document surface are accumulated. However, it can also be applied to a sensor having a thin film sandwich structure in which light receiving elements for outputting in time series, for example, photodiodes reverse-biased by a constant voltage are arranged in an array.

[0020]

According to the present invention, the bias optical signal output from the bias light photoelectric conversion element and the signal output from the photoelectric conversion element are output as a time-series signal of one line by the drive circuit, and the bias optical signal output is obtained. Since the signal output is corrected by sampling the holding circuit and performing differential compensation with the signal output, the bias optical signal output can be sampled for each line to perform differential compensation, and the bias optical signal component By enabling correction in real time, an image signal faithful to the original image can be obtained. Also, since the bias optical signal component can be corrected in real time,
The bias light signal component can be corrected before conversion into a digital signal, and the resolution level is increased by allocating all the resolution levels of the A / D converter in digital processing to the reflected light component of the original, thereby increasing the resolution of the original image signal. It is possible to improve the gradation reproducibility.

[Brief description of drawings]

FIG. 1 is an explanatory plan view showing an embodiment of a solid-state imaging device of the present invention.

FIG. 2 is a cross-sectional explanatory view taken along the line AA ′ of FIG.

FIG. 3A is a plan view of a photoelectric conversion element, and FIG.
FIG. 7A is a sectional view taken along line BB ′ of FIG.

FIG. 4 is a simplified equivalent circuit diagram of the solid-state imaging device.

FIG. 5 is a simplified equivalent circuit diagram of a differential compensation circuit.

FIG. 6 is a timing chart diagram for explaining a reading operation of the solid-state imaging device.

FIG. 7 is an explanatory plan view of a solid-state imaging device according to another embodiment.

8 is a cross-sectional view taken along the line CC ′ of FIG. 7.

FIG. 9 is a cross-sectional explanatory view showing a conventional example of an image sensor using bias light.

[Explanation of symbols]

11 ... Insulating transparent substrate, 12 ... Photoelectric conversion element, 12
a ... Metal electrode, 12b ... Photoelectric conversion layer, 12c ... Transparent electrode, 13 ... Sensor array, 14 ... Light-shielding film, 15
... Bias light photoelectric conversion element, 16 ... Driving IC,
18 ... Differential compensation circuit, 19 ... Driving circuit, 30 ... Bias illumination light source, 32 ... Original illumination light source, 33 ... Original surface

Claims (1)

[Claims] 1. A solid-state imaging device comprising: a photoelectric conversion element formed on a transparent insulating substrate for receiving reflected light from a document surface; and light source means for irradiating the photoelectric conversion element with bias light. A photoelectric conversion element for bias light, which is formed in the vicinity of the photoelectric conversion element and shields the reflected light and receives only the bias light, a bias optical signal output from the photoelectric conversion element for the bias light, and the photoelectric conversion element Drive circuit for outputting the reflected light signal in the order of the reflected light signal output, a holding circuit for sampling each signal separately, and a differential circuit for outputting the difference between the held reflected light signal output and the bias light signal output. A solid-state imaging device comprising: a compensating unit.