JP5040820B2 - Image reading apparatus and method for controlling image reading apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus and an image reading apparatus control method, and more particularly to an image reading apparatus capable of reading a two-dimensional image and an image reading apparatus control method.

  An electrophotographic image forming apparatus (scanner function, facsimile function, copying function, function as a printer, data communication function, and MFP (Multi Function Peripheral) having a server function, facsimile apparatus, copying machine, etc.) A scanner (an example of an image reading apparatus) that reads an image from a document is provided.

  As a structure of a scanner, one that acquires a two-dimensional image by mechanically scanning a plurality of image pickup devices arranged in one dimension is common. There has also been proposed a scanner that reads an image in a short time using a two-dimensional contact area sensor without a mechanical movement mechanism. Such a scanner performs two-dimensional reading by arranging a plurality of pixels vertically and horizontally. One pixel area is divided into a light emitting area and a light receiving area. The elements in the light emitting area emit light, and the reflected light from the original is received by the elements in the light receiving area (photoelectric conversion unit), whereby image data in the pixel is acquired.

  Since such an apparatus does not require mechanical scanning, problems such as instability, durability deterioration, and noise associated with scanning can be eliminated, and the apparatus can be miniaturized. Therefore, these devices are attracting attention as new document reading devices.

  In a document reading apparatus using a two-dimensional contact area sensor, a CMOS sensor with low power consumption is preferably used for the photoelectric conversion unit. As such a sensor, for example, an embedded photodiode can be used. The peripheral circuit includes a transfer gate portion, a floating diffusion portion (a signal charge storage portion, also referred to as an “FD portion”), and a reset gate portion, and performs correlated double sampling processing to perform image signal processing. It is conceivable to reduce noise.

In Patent Document 1 below, a pixel included in an area sensor includes an EL (electroluminescence) element as a light source and a photodiode as a photoelectric conversion element, and the operation of the EL element and the photodiode is controlled by a TFT (thin film transistor). A close contact area sensor is described. In addition, a configuration of a photoelectric conversion circuit including three transistors for one photodiode is disclosed.
JP 2001-292276 A

  A document reading apparatus using a two-dimensional contact area sensor includes a light source / sensor layer sandwiched between an ITO (indium tin oxide) layer for power supply and control and a substrate. A document on the ITO layer is read.

  In a normal contact area sensor, the number of pixels to be read (A3 original; 75 million pixels at 600 dpi reading, 300 million pixels at 1200 dpi reading), and when reading the entire image at once, each pixel It takes time until the charge amount of the signal charge for all the pixels is detected after the photoelectrically converted signal charge is transferred and accumulated in the FD portion. For this reason, there is a problem that the amount of charge fluctuates due to the addition of electrons thermally excited in the semiconductor to the signal charge accumulated in the FD portion, and the amount of noise in the image signal increases.

  FIG. 9 is a timing chart of a document reading apparatus using a conventional two-dimensional contact area sensor.

  At time T1, the transfer pulse (D) for each pixel is turned ON. As a result, the charge (A) in the photodiode is discharged once. The time (time T1 to T3) until the transfer pulse (D) is turned on again after a certain time is the image reading time.

  Prior to the second transfer pulse ON (time T3), the charge (B) in the FD section is reset by turning on the reset pulse (C) at time T2. As a result, the amount of charge generated by photoelectric conversion by the photodiode can be accurately reproduced as the amount of charge in the FD portion by the transfer pulse at time T3.

  However, the amount of charge accumulated in the FD portion changes over time due to the mixing of electrons thermally excited inside the semiconductor. Even when charges generated in the pixels of the entire reading unit are transferred to the FD unit of each pixel at a time, the charge detection cannot be performed at a time. For this reason, a time difference occurs between the first charge detection and the last charge detection (the “sampling timing” in the figure is different for each pixel).

  Therefore, the later the charge detection, there is a possibility that the charge has fluctuated from the charge initially transferred to the FD section, and it becomes difficult to accurately grasp the amount of light received by the photodiode.

  The present invention has been made to solve such a problem, and can improve reading performance in an image reading apparatus that reads a document using a plurality of two-dimensionally arranged image sensors. An object of the present invention is to provide an image reading apparatus and a method for controlling the image reading apparatus.

In order to achieve the above object, according to one aspect of the present invention, an image reading apparatus is an image reading apparatus that reads a document using a plurality of pixel units arranged two-dimensionally, and each of the plurality of pixel units. Includes a light source unit that irradiates a document, a photoelectric conversion unit that detects light from the document, and a charge storage unit that temporarily stores signal charges generated by the photoelectric conversion unit. A charge detection unit that detects the amount of charge accumulated in the unit, and the time from when the signal charge is transferred to the charge storage unit until it is detected by the charge detection unit is substantially reduced in all of the plurality of pixel units. The image reading timing in the photoelectric conversion unit is controlled so as to be constant.

  Preferably, the image reading apparatus performs control so that the plurality of pixel portions partially read at different timings and sequentially read.

  Preferably, the image reading apparatus further includes a charge reset unit for removing the signal charge accumulated in the charge accumulation unit after the charge detection by the charge detection unit.

  Preferably, the light emission of each of the plurality of pixel units is controlled independently for each pixel unit, and the light source unit in the reading target pixel emits light to acquire an image signal of the reading target pixel.

  Preferably, the light source unit includes an electroluminescence element, and light emission thereof is controlled by a thin film transistor arranged for each pixel.

  Preferably, the light source unit includes a white backlight light source, a color filter, and a liquid crystal panel, and light emission thereof is controlled by a thin film transistor disposed for each pixel.

According to another aspect of the present invention, in the control method of an image reading apparatus that reads a document using a plurality of pixel units arranged two-dimensionally, each of the plurality of pixel units includes a light source unit that irradiates the document and The method includes: a photoelectric conversion unit that detects light from a document; and a charge storage unit that temporarily stores signal charges generated in the photoelectric conversion unit, and a method that detects a charge amount stored in the charge storage unit. The photoelectric conversion unit includes a detection step so that the time from when the signal charge is transferred to the charge storage unit until it is detected by the charge detection step is substantially constant in all of the plurality of pixel units. The image reading timing is controlled.

  According to these inventions, an image reading apparatus capable of improving reading performance and an image reading apparatus control method in an image reading apparatus that reads a document using a plurality of image pickup elements arranged in two dimensions are provided. It becomes possible to do.

  Hereinafter, an image reading apparatus according to an embodiment of the present invention will be described. The image reading apparatus includes a plurality of imaging elements arranged in a two-dimensional manner. The image reading apparatus has a light source switching method (with a light source of R (red) → G (green) → B (blue) of equal magnification imaging (the resolution of the sensor (imaging device) itself is equal to the reading resolution of the document itself) A method of obtaining a color image by switching in order is employed. In other words, the image reading apparatus is a contact type two-dimensional image reading apparatus that reads image information of a document with an area type image sensor unit, and performs photoelectric conversion and image processing.

  The image reading apparatus includes a light-emitting layer, a light-emission control unit that controls light emission luminance and light-emission timing, a photoelectric conversion layer that detects reflected light of a placed document, and signal charges generated in the photoelectric conversion layer as image signals. And an image signal control unit for processing as described above.

  A photodiode is used as the image sensor. A photoelectric conversion circuit including four transistors is used for one photodiode. One pixel includes an EL element, a photodiode, and a thin film transistor. The light source need not be an EL element.

  FIG. 1 is a perspective view showing an external appearance of an image reading apparatus according to one embodiment of the present invention.

  Referring to the figure, an image reading apparatus 1 includes a reading unit 2 including a plurality of image pickup elements arranged in two dimensions.

  FIG. 2 is a plan view of the image reading apparatus.

  The reading unit 2 includes a plurality of pixel units 3. One pixel unit 3 includes a light source unit 4 and a sensor unit 5. The light source unit 4 includes a RED light source, a GREEN light source, and a BLUE light source (each shown by different hatching).

  FIG. 3 is a diagram illustrating an outline of a cross-sectional configuration of the reading unit 2.

  The reading unit 2 is configured to sandwich the light source / sensor layer 8 between the power supply and control ITO layer 7 and the substrate 9.

  At the time of image reading, power is supplied to the light source 4 of the light source / sensor layer 8 of the lighting target pixel, and the pixel is turned on. The generated light passes through the transparent ITO layer 7 and is irradiated onto the document 6 placed on the upper surface of the ITO layer 7. As a result, reflected light corresponding to the density of the document is generated.

  The sensor unit 5 of the pixel to be read receives reflected light from the original and generates a voltage corresponding to the reflected light by photoelectric conversion. A voltage generated at each pixel is detected, and a two-dimensional image of the document is reconstructed by the image processing unit.

  The light source unit 4 of each pixel unit 3 lights up three colors of red, blue, and green sequentially, and color reading is possible by detecting the voltage generated in the sensor unit 5 when the light of each color is turned on. .

  Regarding the lighting of the light source, only the light source of the reading target pixel may be turned on with respect to the reading target pixel, the light sources of the adjacent pixels may be turned on, or the light sources of all the pixels may be turned on.

  FIG. 4 is a block diagram illustrating a circuit configuration of the image reading apparatus.

  The reading unit 2 is provided with a plurality of pixel units 3 vertically and horizontally. Which pixel in the X and Y directions is caused to emit light by the column direction driving circuit 125 and the row direction driving circuit 127, which pixel in the X and Y directions is to be read, and which pixel in the X and Y directions is emitted. Whether to be in a standby state where neither reading nor reading is performed is controlled. The column direction driving circuit 125 and the row direction driving circuit 127 have a function of an image signal control unit that processes a signal charge generated in the photoelectric conversion layer of the pixel unit 3 as an image signal.

  In each pixel portion, a thin film transistor is arranged, and thereby light emission is controlled.

  Each of the column direction driving circuit 125 and the row direction driving circuit 127 is connected to the driving circuit 123 and driven by the CPU 121. That is, the reading unit 2 starts a reading operation in accordance with an external reading command, and the read data obtained thereby is output via the CPU 121.

  FIG. 5 is a diagram illustrating a partial circuit configuration of the reading unit 2 of the image reading apparatus.

  In the reading unit 2, the circuits of the plurality of pixel units 3 are arranged in a matrix.

  FIG. 6 is a diagram illustrating a circuit configuration of one pixel unit 3.

  The pixel unit 3 includes a light emitting element 10 and a photodiode 14.

  The light emitting element 10 is controlled by a light source selection transistor 11 and a light source driving transistor 13 (and a capacitor 12) to generate light having a required luminance at a required timing.

  Also, photoelectric conversion, transfer of generated charges, and generation are performed by a combination of the photodiode 14 in the pixel unit 3, the transfer gate unit 15, the charge reset unit 16, the charge detection transistor 17, and the selection transistor 18. The detection of the charge amount is controlled.

  FIG. 7 is a diagram showing a detailed cross-sectional configuration of a portion related to the photodiode 14 of the pixel unit 3.

  When the photodiode 14 is irradiated with light, a charge corresponding to the amount of light is generated in the photodiode 14. When the transfer gate unit 15 is turned on, the charges generated in the photodiode 14 move to the FD unit 19. The potential of the FD unit varies according to the amount of charge transferred to the FD unit 19.

  The potential is detected by the charge detection transistor 17 and extracted as an image signal. The charge accumulated in the FD unit 19 is discharged from the FD unit 19 by turning on the charge reset unit 16.

  FIG. 8 is a timing chart showing the operation of the reading unit 2 of the image reading apparatus.

  In the present embodiment, image reading and charge sampling are performed by the same processing as in FIG. The image reading timing is set in accordance with the sampling timing of the charge of the pixel. Control is performed so that the later the sampling timing, the later the image reading timing.

  In the first pixel that performs sampling earliest, the transfer pulse (D) for the pixel is turned ON at time T1. As a result, the charge (A) in the photodiode is discharged once. The time (time T1 to T3) until the transfer pulse (D) is turned on again after a certain time is the image reading time.

  Prior to the second transfer pulse ON (time T3), the charge (B) in the FD section is reset by turning on the reset pulse (C) at time T2. As a result, the amount of charge generated by photoelectric conversion by the photodiode can be accurately reproduced as the amount of charge in the FD portion by the transfer pulse at time T3. The charge in the FD section is sampled at time T4.

  On the other hand, at the nth pixel whose sampling timing is later than the first pixel, the transfer pulse (D) for the pixel is turned ON at time T1 '(T1' is later than T1). As a result, the charge (A) in the photodiode is discharged once. The time (time T1 'to T3') until the transfer pulse (D) is turned on again after a certain time is the image reading time (this time is substantially equal to the time between times T1 and T3).

  Prior to the second transfer pulse ON (time T3 '), the reset pulse (C) is turned ON at time T2' to reset the charge (B) in the FD section. As a result, the amount of charge generated by photoelectric conversion by the photodiode can be accurately reproduced as the amount of charge in the FD portion by the transfer pulse at time T3 '. The charge in the FD section is sampled at time T4 '.

  By adjusting the image reading start time T1 ', the time between T3 and T4 and the time between T3' and T4 'can be made substantially the same (substantially the same). That is, by shifting the image reading time of each pixel and making the time from charge transfer to the FD unit 19 to charge detection approximately constant for all the pixels, the amount of charge due to the difference in the charge accumulation time in the FD unit 19 Variation can be suppressed.

  Note that the reading start time may be shifted for each pixel, or the reading start time may be shifted for each predetermined number of pixels. For example, the reading start time is shifted for each line (or for each block).

  Further, it is desirable to shift the light emission timing of the light source for pixel reading in accordance with the image reading time of FIG. For example, the light emission of each pixel is controlled at a wider interval with a margin than the interval of “image reading” in FIG. For such control, it is preferable that the plurality of pixel units include a light source unit that can control light emission and luminance independently for each pixel unit. Partially and sequentially, a light source of a reading target pixel (and / or a peripheral pixel of the pixel) within the reading range emits light and reads an image signal of the reading target pixel.

  [Effects of the embodiment]

  According to the embodiment described above, the contact type two-dimensional image reading apparatus provided with the light emitting layer and the sensor layer that receives the reflected light from the document in each pixel partially reads the document image while shifting the timing. The time from when the signal charge generated in each pixel is transferred / stored in the floating diffusion portion to when the charge detection portion of each pixel detects the amount of signal charge is made substantially constant. That is, the time from when the signal charge generated in each pixel is transferred / stored in the floating diffusion unit to when the signal charge is read out by the charge detection unit is made uniform for all the pixels. Thereby, the amount of noise on the entire reading surface can be reduced. Further, the image quality can be made uniform. As a result, a high-quality image reading apparatus can be provided.

  [Others]

  As the light source, an electroluminescence element may be used and light emission may be controlled by a thin film transistor arranged for each pixel, or a white backlight light source, a color filter, and a liquid crystal panel may be used to emit light by a thin film transistor arranged for each pixel. You may control.

  The image reading apparatus may be provided in an image forming apparatus such as a monochrome / color copying machine, a printer, a facsimile machine, or a multifunction peripheral (MFP) thereof.

  In addition, it should be thought that the said embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a perspective view showing an external appearance of an image reading apparatus in one embodiment of the present invention. It is a top view of an image reading apparatus. FIG. 3 is a diagram illustrating an outline of a cross-sectional configuration of a reading unit. It is a block diagram which shows the circuit structure of an image reading apparatus. FIG. 2 is a diagram illustrating a circuit configuration of a part of a reading unit 2 of the image reading apparatus. 2 is a diagram illustrating a circuit configuration of one pixel unit 3. FIG. 3 is a diagram illustrating a detailed cross-sectional configuration of a portion related to a photodiode 14 of the pixel unit 3. FIG. 6 is a timing chart illustrating the operation of the reading unit 2 of the image reading apparatus. 6 is a timing chart of a document reading apparatus using a two-dimensional contact area sensor according to a conventional technique.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Two-dimensional image reader 2 Reading part 3 Pixel part 4 Light source part 5 Sensor part 6 Manuscript 7 ITO layer 8 Light source / sensor layer 9 Substrate 10 Light emitting element 11 Light source selection transistor 12 Capacitor 13 Light source drive transistor 14 Photodiode 15 Transfer Gate part 16 Charge reset part 17 Charge detection transistor 18 Selection transistor 19 FD part (floating diffusion part)

Claims (7)

An image reading apparatus that reads a document using a plurality of pixel units arranged two-dimensionally,
Each of the plurality of pixel portions is
A light source unit for irradiating the document;
A photoelectric conversion unit for detecting light from the document;
A charge storage unit that temporarily stores signal charges generated in the photoelectric conversion unit,
A charge detection unit for detecting the amount of charge stored in the charge storage unit;
The image in the photoelectric conversion unit is such that the time from when the signal charge is transferred to the charge storage unit until it is detected by the charge detection unit is substantially constant in all of the plurality of pixel units. An image reading apparatus that controls reading timing . The image reading apparatus according to claim 1, wherein the plurality of pixel units perform control so that reading is sequentially performed while partially changing timing. 3. The image reading apparatus according to claim 1, further comprising a charge reset unit configured to remove signal charges accumulated in the charge accumulation unit after the charge detection by the charge detection unit. The plurality of pixel portions are controlled to emit light independently for each pixel portion,
Light source unit emits light in the read target pixel, and acquires an image signal of the read object pixel, the image reading apparatus according to any one of claims 1 to 3. The light source unit includes an electroluminescent element, a thin film transistor arranged in each pixel, the light emission is controlled, the image reading apparatus according to any one of claims 1 to 4. The light source unit includes a white backlight source and a color filter and a liquid crystal panel, by a thin film transistor arranged in each pixel, the light emission is controlled, the image reading apparatus according to any one of claims 1 to 4. A method for controlling an image reading apparatus that reads a document using a plurality of pixel units arranged two-dimensionally,
Each of the plurality of pixel portions is
A light source unit for irradiating the document;
A photoelectric conversion unit for detecting light from the document;
A charge storage unit that temporarily stores signal charges generated in the photoelectric conversion unit,
A charge detection step of detecting the amount of charge stored in the charge storage unit;
In the photoelectric conversion unit, the time from when the signal charge is transferred to the charge storage unit until it is detected in the charge detection step is substantially constant in all of the plurality of pixel units. An image reading apparatus control method for controlling image reading timing .

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