JP2000295413A - Image sensor and its driving system - Google Patents

Abstract

(57) [PROBLEMS] To solve the deterioration of the spatial resolution of an image sensor, a polarization control element such as a liquid crystal element described above and a birefringent medium having a birefringence effect are combined to determine an optical axis from a subject. , The position information between the image pickup pixel pitches is interpolated to improve the resolution. SOLUTION: A photoelectric conversion element array 101 for receiving light,
In an image sensor comprising an illuminating device 3 and a lens 2 for forming optical information of an original on the array of photoelectric conversion elements, a subject is obtained by combining a polarization control element 6 for rotating a polarization plane and a birefringent medium 7 having a birefringence effect. An image sensor comprising: means for shifting an optical axis from a camera in a predetermined direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor.

[0002]

2. Description of the Related Art In recent years, with the rapid spread of personal computers, high performance of computers, and development of networks, the area for handling digital image information has been rapidly expanded. In such a situation, it is required that the solid-state imaging device mounted on an image input device such as a scanner or a digital camera further increase the number of pixels and direct high-definition image input. For example, a configuration of a conventional image sensor will be described with reference to a schematic cross-sectional view of FIG. 18 and a schematic plan view of FIG. As shown in the figure, a plurality of sensor ICs 101 having a group of photoelectric conversion elements arranged in a line are accurately arranged on a sensor substrate 102 such as a glass epoxy material in a line in accordance with the length of a document to be read. An array 1, a lens array 2, an illuminating device 3, a cover glass 4 made of a light-transmitting member for supporting a document, and a frame 5 made of a metal such as aluminum or a resin such as polycarbonate for positioning and holding them. It is composed of The lighting device 3 includes R, G,
R, in which B3 color LED elements are packaged in one,
It is composed of a G and B three-color LED chip and a light guide made of a member having excellent light transmittance such as acrylic resin.

The respective functions are as follows. The illuminating device 3 sequentially illuminates R, G, and B three colors of light from a diagonal direction of 45 ° on a document pressed and supported on the cover glass 4 to sequentially illuminate the R, G, and B of the document. The light information of the three colors B is imaged on the sensor IC 101 by the lens array 2, and the sensor IC 101
The B3 color optical information is converted into an electric signal and transmitted to the system, where the R, G and B electric signals are processed to reproduce a color image.

[0004]

However, since the photoelectric conversion element group provided in the sensor IC has a discrete imaging pixel array, the image information of the subject (original) is sampled at the constituent pixel pitch and the position information is obtained. There is a problem that is missing.

[Object of the Invention] An object of the present invention is to solve such a decrease in spatial resolution by combining a polarization controlling element such as the above-mentioned liquid crystal element with a birefringent medium having a birefringent effect. An object of the present invention is to improve the resolution by shifting the axis in a predetermined direction and interpolating the positional information between the imaging pixel pitches.

[0006]

That is, the present invention provides a method of combining a photoelectric conversion element array for receiving light, a polarization control element for rotating a polarization plane, and a birefringent medium having a birefringence effect, from an object. The optical axis is shifted in a predetermined direction.

[0007] The polarization controlling element has a structure in which at least one kind of liquid crystal such as a ferroelectric liquid crystal, an antiferroelectric liquid crystal, and a twisted nematic liquid crystal is filled between optically transparent opposing electrodes. .

According to the present invention, as the polarization control, the phase of the incident light to the liquid crystal element is modulated by switching the applied voltage to rotate the plane of polarization, and the light emitted from the liquid crystal element is controlled by the presence or absence of the rotation. The optical axis can be selectively shifted in a predetermined direction by the birefringence effect of the birefringent medium, and it is necessary to change the image pickup pixel interval of the sensor, or to mechanically move a mirror for shifting the optical axis, the sensor itself, etc. And the resolution can be easily improved.

[0009]

[Embodiment 1] First, FIG. 5 shows the principle of occurrence of optical axis shift due to a birefringent medium. The angle between the extraordinary optical axis 109 of the quartz plate 8 as the birefringent medium and the incident optical axis is β, and the thickness of the quartz plate is d. At this time, ordinary light (polarized wave perpendicular to the paper) travels straight, while extraordinary light (polarized wave parallel to the paper) travels obliquely and shifts by L. This shift amount L is expressed by the following equation.

[0010]

(Equation 1) Here, the refractive index no of ordinary light and the refractive index n of extraordinary light of the quartz plate
e is ne = 1.55336, no = 1.54425. Now, the resolution of the image sensor of 600 dpi is set to 2
In order to double the value, β = 45 ° and d =
It may be set to 3.4 mm.

As a polarization control element, as shown in FIG.
A transparent electrode 104 is provided on a transparent substrate 103 made of glass or the like like ITO, and a liquid crystal alignment film 105 is further formed thereon.
And a liquid crystal 10 having a thickness of 1 μm.
7 is used. As the liquid crystal material,
A ferroelectric liquid crystal having a fast response speed is effective. Further, in the above example, the liquid crystal element is manufactured using a transparent substrate different from the quartz plate, but in order to further reduce cost and weight,
A crystal plate may be used in place of the transparent substrate to be integrated with the liquid crystal element.

FIGS. 3 and 4 are schematic diagrams showing a case where the quartz plate and the liquid crystal element are applied to the image sensor of the present invention. As shown in FIG. 3, when the switch state of the ferroelectric liquid crystal element 7 is state 1, the irradiation light component a from the subject 9 side
Since the polarization plane and the extraordinary optical axis 108 make an angle of about 45 ° after passing through the lens 10, the stop 11, and the polarizing plate 6, the transmitted light rotates in the direction of the extraordinary optical axis, and the linearly polarized light ( (x-axis direction) → elliptical polarization → circular polarization → elliptical polarization → linear polarization (y-axis direction) in the ferroelectric liquid crystal element 7, the polarization plane is rotated by 90 ° from the initial state, and is irradiated on the quartz plate 8. You. In the crystal plate 8, since the extraordinary optical axis 109 of the crystal is not included in the incident polarization plane, the optical axis is maintained without being refracted, exits to the air layer again, and is irradiated on the imaging pixels 12 of the sensor.

On the other hand, as shown in FIG.
When the switch state is state 2, the irradiation light component (a + 1) from the subject 9 side passes through the lens 10 and the aperture 11, and is then polarized by the polarizing plate 6 in the pixel shifting direction. Since the polarization plane of the light and the extraordinary optical axis 108 of the ferroelectric liquid crystal element 7 are parallel, the transmitted light is applied to the quartz plate 8 having birefringence while maintaining the polarization plane. In the quartz plate 8, since the extraordinary optical axis 109 of the quartz is included in the incident polarization plane, the light polarized in the x-axis direction is refracted in the direction in which the extraordinary optical axis 109 of the quartz plate is inclined, and returns to the air layer. When the light exits, it becomes parallel to the optical axis, a shift from the optical axis of the incident light occurs, and the light is irradiated on the imaging pixel 12 of the sensor. That is, the (a + 1) portion of the subject 9 is imaged. The resolution can be doubled by making the deviation of the optical axis between the states 1 and 2 half the pixel pitch of the sensor.

FIG. 1 shows a specific arrangement example of the image sensor according to the present invention. Since the light source used for the illumination device 3 in the image sensor is not polarized, a polarizing plate 6 is inserted between the optical path of the illumination device 3 and the liquid crystal element 7. Thus, the polarizing plate 6 is located at the place of the LED light source.
And the liquid crystal element 7 and the crystal plate 8 are arranged between the lens array 2 and the sensor IC 101.

The lens has an aperture angle of 20 deg.
The above-mentioned short focal length 1 × lens array was used.

Further, the illuminating device comprises an LED light source and a light guide for guiding the light of the light source and emitting the light in a desired direction.

FIG. 2 shows a configuration of the lens array 2 to the sensor IC 1.
The state of deviation of the optical axis of the irradiation light on No. 01 is shown. The dotted line is the optical axis between the pixel pitches, and the shift amount L
Only being wobbling. However, the liquid crystal element 7 and the crystal plate 8 are omitted.

As an example of the optical arrangement of the polarizing plate 6, the liquid crystal element 7, the quartz plate 8, etc., the position of the polarizing plate 6 is changed (FIGS. 7 to 8) or the liquid crystal element 7 and the quartz plate 8 are combined. Several cases can be considered, such as a case where the position is changed in a set (FIGS. 9 to 11) and a case where the position is changed individually (FIGS. 12 to 14).

Next, FIG. 15 shows a system configuration diagram of the image sensor thus configured. In FIG.
0 is a main controller for controlling driving of the image sensor, 111 is a control signal generation circuit that generates a clock based on a control signal from the main controller, 112 is R,
LE for generating a signal for controlling the lighting of each of the G and B LEDs
D drive control section, 113 is a wobbling drive control section for generating a signal for modulating a polarization control element for turning on / off wobbling, 114 is a sensor array drive control section for generating a signal for controlling driving of a sensor array, 11
Reference numeral 5 denotes an image sensor unit.

FIG. 16 shows a timing chart of the image sensor driving circuit. (A) is a switching timing of a three-color LED as a light source of a lighting device, (b) is a timing of shifting an optical axis of a subject (= wobbling),
(C) shows the timing at which the optical information from the subject is stored in the sensor, and (d) shows the readout timing from the sensor.

That is, when R is turned on, wobbling is present / absent, and information of a position n where the image information of the subject (original) is sampled at the constituent pixel pitch and a position n + 1 where the spatial resolution is interpolated is sequentially read out by the sensor. .

Next, similarly, when G is turned on, with or without wobbling, the n and n + 1 portions of the original are sequentially read by the sensor, and the sensor reading when B is turned on is completed. The R, G, and B information are all aligned. Therefore, the resolution can easily be doubled. At this time, the image sensor unit 115
Has moved to the next reading line, and the same R, G,
An operation for obtaining the B signal is performed. By repeating this series of operations while moving the image sensor unit 115 line by line in the sub-scanning direction, a color image on the entire original surface is read.

[Embodiment 2] FIG. 17 shows a drive timing chart of another embodiment 2. That is, first, R,
G and B are sequentially turned on at high speed, and all information of the n portion of the document is read. Next, with wobbling, R, G,
B is sequentially turned on at a high speed, and all information of the (n + 1) -th portion of the document is read. In the first embodiment, since wobbling must be performed at least at a half or less of the light source switching frequency, a high response speed is required for the liquid crystal element (LED switching time is about 1 to 6 msec). In the second embodiment, since the wobbling frequency is lower than that of the first embodiment, a liquid crystal element having a relatively slow response speed can be used.

[0024]

As described above, according to the present invention, the polarization control element for rotating the polarization direction and the birefringent medium having the birefringence effect are combined so that the optical axis from the subject (original document) is directed in a predetermined direction. The resolution can be easily improved without the need to change the image pickup pixel interval in the light receiving element of the image sensor or to perform a mechanical movement of a mirror or a sensor itself for shifting the optical axis.

Further, the polarization control element has a structure in which a liquid crystal composed of at least one of ferroelectric liquid crystal, antiferroelectric liquid crystal, twisted nematic liquid crystal and the like is filled between optically transparent counter electrodes. , Can be controlled electrically.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mounting example of an image sensor according to the present invention.

FIG. 2 is a schematic diagram of wobbling in a mounting example of the image sensor of the present invention.

FIG. 3 is a schematic diagram of an image sensor of the present invention using a liquid crystal cell and a quartz plate as a wobbling element in state 1;

FIG. 4 is a schematic view of an image sensor according to the present invention in state 2;

FIG. 5 is a principle diagram of optical axis shift due to a birefringent medium.

FIG. 6 is a cross-sectional view of a liquid crystal cell as a polarization control element.

FIG. 7 is a cross-sectional view of another mounting example of the present invention.

FIG. 8 is a cross-sectional view of still another mounting example of the present invention.

FIG. 9 is a cross-sectional view of still another mounting example of the present invention.

FIG. 10 is a cross-sectional view of still another mounting example of the present invention.

FIG. 11 is a sectional view of still another mounting example of the present invention.

FIG. 12 is a cross-sectional view of still another mounting example of the present invention.

FIG. 13 is a sectional view of still another mounting example of the present invention.

FIG. 14 is a cross-sectional view of still another mounting example of the present invention.

FIG. 15 is a system configuration diagram of the image sensor of the present invention.

FIG. 16 is a drive timing chart of the image sensor according to the first embodiment of the present invention.

FIG. 17 is a drive timing chart according to the second embodiment of the present invention.

FIG. 18 is a schematic sectional view showing the structure of a conventional image sensor.

FIG. 19 is a schematic plan view showing the structure of a conventional image sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sensor array 2 Lens array 3 Lighting device 4 Cover glass 5 Frame 6 Polarizer 7 Liquid crystal element 8 Quartz plate 9 Subject 10 Lens 11 Aperture 12 Image sensor 101 Sensor IC 102 Sensor substrate 103 Transparent substrate 104 Transparent electrode 105 Alignment film 106 Sealing material 107 Liquid crystal 108 Abnormal optical axis 109 Abnormal optical axis 110 Main controller 111 Control signal generation circuit 112 LED drive control unit 113 Wobbling control unit 114 Sensor array drive control unit 115 Image sensor unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA02 BA06 BA42 BB03 BB05 BB61 BC21 2H088 EA47 HA06 HA18 HA24 JA05 JA13 JA17 JA20 MA20 4M118 AA10 AB01 FA08 FB08 GA04 GA10 GD02 HA23 5C024 AA01 AA03 CA11 EA04 FA11 FA01 BA04 DA03 DB01 DB04 DB08 DB22 DB29 DC02 DC04 DC05 DC07 DE02 DE29

Claims (8)

[Claims] 1. An array of photoelectric conversion elements for receiving light, and means for shifting an optical axis from a subject in a predetermined direction by combining a polarization control element for rotating a polarization plane and a birefringent medium having a birefringence effect. An image sensor comprising: 2. The polarization control element according to claim 1, wherein a liquid crystal comprising at least one of ferroelectric liquid crystal, semi-ferroelectric liquid crystal, and twisted nematic liquid crystal is filled between the optically transparent counter electrodes. The image sensor according to claim 1, wherein: 3. The image sensor according to claim 1, wherein the image sensor includes a lens for forming optical information of a subject on the photoelectric conversion element array and a lighting device. 4. The lens has an aperture angle of 20 deg. 4. The image sensor according to claim 3, wherein said short focal length, equal magnification type lens array is used. 5. The image sensor according to claim 3, wherein the illumination device includes an LED light source and a light guide that guides light from the light source and emits light in a desired direction. 6. The image sensor according to claim 3, wherein a polarizing plate is disposed between the optical path of the illumination device and the polarization control element. 7. The liquid crystal display device according to claim 3, wherein a polarizing plate is inserted between an optical path between the light source of the lighting device and the liquid crystal element, and a liquid crystal element and a quartz plate are arranged between the lens array and the sensor IC. Image sensor. 8. A drive system for driving the image sensor according to claim 3, wherein a main controller controls driving of the image sensor, and a control signal that generates a clock based on a control signal from the main controller. A generation circuit, an LED drive control unit that generates a signal for controlling the lighting of each of the R, G, and B LEDs that illuminate the original, a wobbling drive control unit that generates a signal that modulates a polarization control element for turning on / off wobbling An image sensor driving system, comprising: a sensor array driving control unit that generates a signal for controlling driving of the sensor array.