JP2018011358A - Image pickup device, image reading apparatus, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup device that can accelerate image reading, an image reading apparatus, and an image forming apparatus.SOLUTION: An image pickup device comprises a plurality of photoelectric conversion elements; and an AD conversion part that performs A/D conversion for every pixel group formed of a plurality of photoelectric conversion elements selected from the plurality of photoelectric conversion elements. Each of the photoelectric conversion elements forming the pixel group is connected to the AD conversion part corresponding to the pixel group with bus lines having a distance in which a signal can be transmitted within a predetermined time.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an image sensor, an image reading apparatus, and an image forming apparatus.

  Conventionally, CCDs are often used as photoelectric conversion elements in scanners that read images, but CMOS linear sensors are attracting attention due to recent demands for low power consumption. The CMOS linear sensor is the same as the CCD in that incident light is photoelectrically converted by a photodiode. The CCD performs charge-voltage conversion on the charge transferred by the shift register by the charge detection unit. On the other hand, a CMOS linear sensor is known to have lower power consumption than a CCD because it converts charges into voltage signals by a charge detection unit for each pixel and outputs each voltage signal via a switch. .

  However, in the conventional CMOS linear sensor, in order to transmit an analog image signal via an analog bus, the analog bus is connected over all pixels and becomes long. Therefore, there is a problem that the wiring resistance and the wiring capacity are large and the speed cannot be increased.

  In addition, as a conventional technique, in Patent Document 1, in order to scan one line, a block divided into three is controlled to be divided into three times, and the first block is scanned in the first, second, and third scans. A sensor that simultaneously scans divided blocks of different colors in the second block and the third block is disclosed.

  However, conventionally, the wiring resistance and wiring capacity of the analog bus cannot be reduced, and the speed of the CMOS linear sensor cannot be increased.

  The present invention has been made in view of the above, and an object of the present invention is to provide an image sensor, an image reading apparatus, and an image forming apparatus that enable high-speed image reading.

  In order to solve the above-described problems and achieve the object, the present invention provides an A for each pixel group including a plurality of photoelectric conversion elements and a plurality of photoelectric conversion elements selected from the plurality of photoelectric conversion elements. Each photoelectric conversion element constituting the pixel group has a distance that can be transmitted within a predetermined time with respect to the AD conversion unit corresponding to the pixel group. Each is connected by a bus line.

  According to the present invention, it is possible to increase the speed of image reading.

FIG. 1 is a diagram illustrating an outline of an image reading apparatus. FIG. 2 is a timing chart showing an operation for driving the CMOS linear sensor shown in FIG. FIG. 3 is a diagram illustrating an outline of the configuration of the image sensor according to the first embodiment. FIG. 4 is a diagram showing a configuration of the pixel shown in FIG. FIG. 5 is a diagram illustrating the periphery of an AD conversion unit that performs A / D conversion on signals output from the pixels illustrated in FIG. 3. FIG. 6 is a timing chart showing the operation of driving the image sensor. FIG. 7 is a diagram schematically illustrating the color of an image read and reproduced by the image sensor. FIG. 8 is a diagram illustrating an outline of the configuration of the image sensor according to the second embodiment. FIG. 9 is a diagram showing a configuration of the pixel shown in FIG. FIG. 10 is a diagram illustrating the periphery of an AD conversion unit that performs A / D conversion on a signal output from the pixel illustrated in FIG. 8. FIG. 11 is a diagram schematically illustrating the color of an image read and reproduced by the image sensor. FIG. 12 is a diagram illustrating an outline of the configuration of the image sensor according to the third embodiment. FIG. 13 is a diagram illustrating the periphery of an AD conversion unit that performs A / D conversion on a signal output from the pixel illustrated in FIG. 12. FIG. 14 is a timing chart illustrating an operation of driving the image sensor. FIG. 15 is a diagram illustrating an outline of a configuration of an image sensor according to the fourth embodiment. FIG. 16 is a diagram showing a configuration of the pixel shown in FIG. FIG. 17 is a diagram illustrating the periphery of an AD conversion unit that performs A / D conversion on a signal output from the pixel illustrated in FIG. 15. FIG. 18 is a timing chart showing an operation for driving the image sensor. FIG. 19 is a diagram showing an outline of a configuration of a CMOS area sensor of a comparative example. FIG. 20 is a diagram illustrating an outline of an image forming apparatus including an image reading apparatus having an image sensor, for example.

  First, the background that led to the present invention will be described. FIG. 1 is a diagram showing an outline of the image reading apparatus 1. The image reading apparatus 1 includes a CMOS linear sensor 10, an AFE (Analog front end) 12, and a timing control unit (TG: Timing Generator) 14.

  The CMOS linear sensor 10 includes a photodiode (PD: photoelectric conversion element) 100, a charge detection unit (Cfd) 102, and a switch (SW) 104 for every n pixels, and outputs an image signal from the output buffer 106. For example, the PD 100 photoelectrically converts reflected light (incident light) from a document. The charge detection unit 102 converts the charge accumulated by the PD 100 by photoelectric conversion into a voltage signal. The image signal converted into a voltage signal is input to the analog bus via the switch 104 and output from the output buffer 106.

  Specifically, each switch 104 outputs an image signal for each pixel by sequentially switching from the 1st to nth pixels. The CMOS linear sensor 10 has, for example, about 7000 pixels (n = about 7000) in order to read an A3 document. Hereinafter, description will be made assuming that n = 7000.

  A drive signal (S [7000]) for driving the switch 104 is a signal that is turned ON once in one line period. However, since a plurality of pixels cannot be turned on at the same time, the timing at which the pixels are turned on is slightly different for each pixel. That is, a signal (S [7000: 1]) for driving each switch 104 is a signal that is asserted once with a pixel period width in one line period, and the number of signals is the same as the number of pixels.

  Similarly, a signal (TS [7000: 1]) for transferring the charge accumulated in the PD 100 to the charge detection unit 102 and a signal (RS [7000: 1]) for resetting the charge detection unit 102 are also one line period. The number of signals is the same as the number of pixels.

  In FIG. 1, only one pixel is described for each of Pix1 to Pix (n) serving as pixel positions in the reading target. However, incident light is converted into RGB three-color electrical signals by RGB three-color filters. In the case of taking out by converting into a pixel, pixels for three colors (approximately 7000 pixels × 3 colors) are arranged in an array for each color.

  The AFE 12 includes an AD conversion unit (ADC) 120 and the like, and converts an image signal output from the CMOS linear sensor 10 from an analog signal to a digital signal. Further, the AFE 12 may include a high-speed serial signal conversion unit (for example, LVDS, VbyOne, etc.) for transmitting the digitally converted image signal to the subsequent image processing unit. The timing control unit 14 outputs a control signal for controlling the CMOS linear sensor 10, a signal for controlling the AFE 12, and the like.

  The AFE 12 and the timing control unit 14 may be configured with one chip, or the CMOS linear sensor 10, the AFE 12, and the timing control unit 14 may be configured with one chip. In addition, the CMOS linear sensor 10 has a large size of the switch 104 for each pixel and a wide analog bus width to increase the speed, thereby reducing impedance and suppressing signal deterioration due to high-speed driving. It may be configured as follows. However, in this case, since the load due to the parasitic capacitance of the switch 104 and the wiring capacitance of the analog bus inevitably increases, there is a factor that hinders high-speed driving.

  FIG. 2 is a timing chart showing an operation for driving the CMOS linear sensor 10 shown in FIG. A drive signal for the CMOS linear sensor 10 is generated by the timing control unit 14 using a reference clock (CLK).

  First, the timing control unit 14 turns on RS prior to the start of a line (reading for each line). RS is a signal for resetting the charge of the charge detection unit 102, and the reset state is released (OFF) during the period of reading the pixel signal.

  The timing control unit 14 transfers the charge from the PD 100 to the charge detection unit 102 by turning on the transfer signal (TS) while the reset state of the charge detection unit 102 is released. The charge detection unit 102 performs charge-voltage conversion.

  Next, the timing control unit 14 turns on the switch control signal (S) for controlling the switch 104, and sends the voltage-converted image signal to the analog bus. The analog bus is a bus to which outputs of all the pixels are connected. At a certain timing, only one selected pixel is connected, and the other pixels are not connected by the switch 104. Thus, the CMOS linear sensor 10 uses an analog bus in which all pixel signals are common.

  The image signal output to the analog bus is output to the outside via the output buffer 106. Thereafter, the timing controller 14 closes the switch 104 by turning off the switch control signal (S), and proceeds to processing of the next pixel. The timing control unit 14 performs this series of operations until all pixel signals are output. Therefore, the timing of TS [n], RS [n], and S [n] is shifted by one pixel period, and one series of operations is performed about 7000 times in one line period. The CMOS linear sensor 10 includes analog buses for three colors of RGB when outputting RGB three-color image signals.

  Note that lsync is a line synchronization signal and indicates the period of one main scanning line of image data. The image reading device 1 sequentially A / D converts the pixel data output from the CMOS linear sensor 10 by the AFE 12, converts it to, for example, a high-speed serial signal, and outputs it to the subsequent stage.

  Since the above operation is performed over all the pixels of the CMOS linear sensor 10, the timing control unit 14 drives the pixels at a pixel frequency of several to several tens of MHz. The CMOS linear sensor 10 drives the operation for one clock of the pixel frequency 7000 times (driven by 7000 signals). When the CMOS linear sensor 10 is operated at a high speed, it is necessary to increase the switch 104 to reduce the impedance and to increase the analog bus wiring for transferring the analog signal for 7000 pixels in order to prevent deterioration of the signal waveform. is there. However, if the switch 104 is enlarged for high-speed operation, the parasitic capacitance increases. Further, when the analog bus is thickened, the wiring capacity increases. That is, since the signal waveform is distorted, high-speed operation is hindered.

(First embodiment)
Next, the image sensor according to the first embodiment will be described. FIG. 3 is a diagram illustrating an outline of the configuration of the image sensor 20 according to the first embodiment. The image sensor 20 is a CMOS in which, for example, Pix1 to Pix (n) that are pixel positions in a reading target can be read in three colors of RGB, and n pixels (pixel portions) are arranged in one direction for each color. It is a color linear sensor. Hereinafter, substantially the same components as the components of each image sensor are denoted by the same reference numerals.

  The pixel 200 provided with an R filter (not shown) includes a photodiode (PD_r) and a pixel block (pixblk_r). A pixel 202 provided with a G filter (not shown) includes a photodiode (PD_g) and a pixel block (pixblk_g). The pixel 204 provided with the B filter (not shown) includes a photodiode (PD_b) and a pixel block (pixblk_b). Each pixel block includes a charge detection unit (Cfd) (not shown) that converts the charge accumulated in the photodiode (photoelectric conversion element) into a voltage, a circuit that drives Cfd, and the like. Hereinafter, the photodiode may be referred to as PD_ *, and the pixel block may be referred to as pixblk_ *. Note that the subscript * represents one of the colors r, g, and b.

  The imaging device 20 has n pixels 200, 202, 204, and AD converters (ADC), and the image signals obtained by performing A / D conversion by the n ADCs are converted into parallel serial converters ( PS) 206 is configured to output serially for each color.

  For example, the image sensor 20 accumulates reflected light (incident light) from a document as a charge by PD_ *, and converts the accumulated charge into a voltage by Cfd of pixblk_ *. The image sensor 20 performs A / D conversion on the image signal by a common ADC provided in the vicinity of each pixel group including a plurality of pixels. Here, the vicinity means, for example, that a difference in distance from each of a plurality of pixels constituting the pixel group to the ADC does not differ by an order of magnitude (or more than 2 orders of magnitude) or the like within a predetermined time. Each signal can be transmitted.

  The imaging device 20 makes three pixels of the same color adjacent in the arrangement direction (main scanning direction) for each color as one pixel group (a range surrounded by a black thick line in FIG. 3 is one pixel group), and for each pixel group. One ADC (common ADC) is used. That is, the image sensor 20 immediately A / D-converts the analog signal from the Cfd of pixblk_ * by the nearby ADC, so that the analog bus length is extremely shortened, and the speed can be increased.

  In the image pickup device 20, all ADCs simultaneously A / D-convert image signals output from all pixel groups for each pixel in the pixel group. The image sensor 20 converts the image data of digital signals output by all ADCs in parallel for each pixel group into serial data (Dout (r), Dout (g), Dout (b)) by the parallel-serial conversion unit 206. And output to the subsequent stage.

  The image sensor 20 is not limited to grouping (selecting) three pixels as a pixel group. For example, in the same way as when the image sensor 20 outputs one line divided into two parts, an EVEN pixel and an ODD pixel, the image sensor 20 uses six pixels (two RGB pixels each as an EVEN pixel and an ODD pixel) as one pixel group. May be shared.

  FIG. 4 is a diagram showing a configuration of the pixel shown in FIG. FIG. 3 shows an example in which three pixels of the same color are processed in parallel as one pixel group, but in FIG. 4, the description will be given focusing on the B pixel group of the image sensor 20.

  Vdd is a power supply voltage supplied to the image sensor 20 and is an output reference potential. Each PD_b accumulates electric charge according to the intensity of incident light. The reset signals (RS1, RS2, RS3) are signals that reset the charge detection unit (Cfd) that converts the charge accumulated in the PD_b into a voltage. The transfer signals (TS1, TS2, TS3) are signals that are transmitted to Cfd that converts the charge accumulated in PD_b into a voltage.

  In FIG. 4, a range including Cfd surrounded by a dotted line is a pixel circuit (pixblk_b). The analog signals (A_sig_b1, A_sig_b2, A_sig_b3) converted into voltages by pixblk_b are transferred according to transfer signals (ADTS1, ADTS2, ADTS3) to the ADC provided in the vicinity of the pixel 204 (PD_b and pixblk_b).

  Note that in the imaging device 20, each signal (RS, TS, ADTS) is input in parallel to each pixel group. However, these signals (RS, TS, ADTS) are common to other pixel groups.

  FIG. 5 is a diagram illustrating the periphery of an AD conversion unit (ADC) that performs A / D conversion on the signal output from the pixel illustrated in FIG. 3. The analog signals (A_sig_b1, A_sig_b2, A_sig_b3) output from the pixel 204 are transferred to the ADC by three transfer signals (ADTS1, ADTS2, ADTS3) having different transfer timings.

  The image signal transferred to the ADC is A / D converted pixel by pixel when the signal ADEN for enabling the ADC is High, and the digital signal (D_sig_b1, D_sig_b2) when the transfer signals (ADTS1, ADTS2, ADTS3) are High. , D_sig_b3) is output to the parallel-serial conversion unit 206.

  The image sensor 20 includes an analog memory (storage unit) in front of each ADC, so that A_sig_b1, A_sig_b2, and A_sig_b3 can be simultaneously transferred to the ADC. Pixels) can be read in each color (= global shutter).

  FIG. 6 is a timing chart showing an operation for driving the image sensor 20. Similar to the CMOS linear sensor 10 shown in FIG. 2, for example, the timing control unit 14 generates a drive signal for the image sensor 20 using a reference clock (CLK).

  lsync is a line synchronization signal, and indicates the cycle of one line in the main scanning direction of the image data. Since the image pickup device 20 uses three pixels as one pixel group, the timing control unit 14 first turns on RS1 and resets Cfd before starting the line. Next, the timing control unit 14 turns on RS2 at a timing different from RS1, further turns on RS3 at a timing different from RS1 and RS2, and resets three Cfd of the pixel group once.

  After resetting each Cfd, the timing control unit 14 sequentially turns on TS1 to TS3 at different timings, and transfers the charge accumulated in PD_ * to Cfd. Then, the timing control unit 14 sequentially turns on the ADTSs 1 to 3 at different timings, and inputs analog signals obtained by Cfd charge-voltage conversion to the ADC.

  The image sensor 20 performs the above operation all at once for each pixel group. Note that the ADC outputs 10-bit data by repeating A / D conversion, for example, about 10 times during a period when ADEN is High. The parallel-serial conversion unit 206 performs parallel-serial conversion on the image signal converted into the digital signal, and outputs the image signal to an image processing unit (not shown) in the subsequent stage. The number of A / D conversions described above is not limited to 10 and may be changed according to the required number of image data received by the subsequent image processing unit.

  FIG. 7 is a diagram schematically illustrating the color of an image read and reproduced by the image sensor 20. As described above, the image pickup device 20 uses three ADCs of the same color adjacent in the arrangement direction for each color as one pixel group, and uses one ADC for each pixel group, thereby enabling high-speed image reading. be able to. On the other hand, the image sensor 20 may not be able to faithfully reproduce the color of the read image.

  The image sensor 20 includes one common processing circuit (herein, described as a processing circuit = ADC) for each pixel group in order to realize high speed, and performs parallel processing. On the other hand, since the image pickup device 20 has a plurality of pixels of the same color arranged in an array in the main scanning direction, the pattern of the pixel group generates fixed pattern noise if the characteristics are different for each ADC.

  The fixed pattern noise on the black side (dark part) and white side (bright part) of the read image can be corrected by black shading and white shading. However, when the occurrence of fixed pattern noise is caused by the difference in linearity of each ADC, the effect appears in a halftone, and cannot be corrected by the above-described black and white shading.

  When image reading is performed using the image sensor 20, the pixel 200, the pixel 202, and the pixel 204 are moved by physically moving the object to be read or the image sensor 20 itself, so that the same main scanning position (pixels at the same position of the object to be read; For example, it is possible to acquire image data of a pixel at the position of Pix1. At this time, when a gray original with a uniform density in RGB (black and white halftone) is read, the linearity is the same among the three R pixels, the three G pixels, and the three B pixels that share the same ADC. Because it is (common), there is no color difference.

  However, in an RGB image at the same pixel position, that is, an image obtained by finally combining RGB (for example, an image at a Pix1 position in the main scanning direction), a characteristic difference between the three ADCs occurs in each image. Unevenness occurs or the color becomes false. In the first place, color unevenness and false color do not occur in each ADC if there is no difference in linearity. However, as long as each ADC is a physically different circuit, there may be a difference in linearity between each ADC. Although it is possible to correct the linearity for each pixel, the correction circuit for that purpose becomes enormous and the control thereof becomes complicated.

(Second Embodiment)
Next, an image sensor according to the second embodiment will be described. FIG. 8 is a diagram illustrating an outline of the configuration of the image sensor 30 according to the second embodiment. The image sensor 30 is a CMOS in which, for example, Pix1 to Pix (n), which are pixel positions in a reading target, can be read in three colors of RGB, and n pixels (pixel portions) are arranged in one direction for each color. It is a color linear sensor.

  However, the image pickup device 20 shown in FIG. 3 has three pixels of the same color adjacent in the arrangement direction for each color as one pixel group, whereas the image pickup device 30 is different from the image pickup device 20 in the configuration of the pixel group. . The image pickup device 30 surrounds pixels of all colors that can be read at the same position in the arrangement direction (main scanning direction) for each color of pixels with one pixel group (indicated by a thick black line in FIG. 8). The range is one pixel group), and one ADC (common ADC) is used for each pixel group. That is, the image pickup device 30 is a single pixel that is a plurality of pixels (here, three pixels of RGB) that can read the same position of the read target by physically moving the read target or the image pickup device 30 itself. A group. Further, the image sensor 30 is not limited to three pixels as one image group. For example, the imaging element 30 may have 6 pixels (RGB 3 pixels × 2) as one pixel group.

  FIG. 9 is a diagram showing a configuration of the pixel shown in FIG. RS1 is a signal that resets the charge detection unit (Cdf) that converts the charge accumulated in PD_r into a voltage. RS2 is a signal that resets the charge detection unit (Cdf) that converts the charge accumulated in PD_g into a voltage. RS3 is a signal that resets the charge detection unit (Cdf) that converts the charge accumulated in PD_b into a voltage.

  TS1 transmits the charge to the charge detection unit (Cfd) that converts the charge accumulated in PD_r into a voltage. TS2 transmits the charge to the charge detection unit (Cfd) that converts the charge accumulated in PD_g into a voltage. TS3 transmits the charge to the charge detection unit (Cfd) that converts the charge accumulated in PD_b into a voltage.

  Analog signals (A_sig_r, A_sig_g, A_sig_b) obtained by converting charges into voltages by pixblk_r, pixblk_g, and pixblk_b, respectively, are transferred to the ADC according to different transfer signals (ADTS1, ADTS2, ADTS3).

  The image pickup device 20 and the image pickup device 30 have different pixel grouping, but each performs parallel processing with three pixels as one pixel group, and thus each signal (RS, TS, ADTS) is required. It is said that. Each of these signals (RS, TS, ADTS) is in common with other pixel groups.

  FIG. 10 is a diagram showing the periphery of an AD conversion unit (ADC) that performs A / D conversion on signals output from the pixels shown in FIG. Analog signals (A_sig_r, A_sig_g, A_sig_b) output from the pixels 200, 202, and 204 are transferred to the ADC during the High period of the transfer signals (ADTS1, ADTS2, ADTS3) having different transfer timings.

  The image signal transferred to the ADC is A / D converted pixel by pixel when the signal ADEN for enabling the ADC is High, and the digital signal (D_sig_r, D_sig_g) while the transfer signal (ADTS1, ADTS2, ADTS3) is High. , D_sig_b) is output to the parallel-serial conversion unit 206.

  Note that the timing for driving the image sensor 30 is the same as the operation for driving the image sensor 20 shown in FIG. 6 (the colors of RGB differ depending on the pixel group).

  FIG. 11 is a diagram schematically illustrating the color of an image read and reproduced by the image sensor 30. As described above, the image pickup element 30 includes pixels of all colors that can read the reading target at the same position in the arrangement direction for each pixel color as one pixel group. Accordingly, the linearity of the ADC appearing in the image data read by the pixel 200, the pixel 202, and the pixel 204 at the same position to be read is also common (same). That is, the image sensor 30 can prevent the occurrence of color unevenness and false color due to fixed pattern noise in halftones that cannot be corrected by black and white shading.

(Third embodiment)
Next, an image sensor according to the third embodiment will be described. FIG. 12 is a diagram illustrating an outline of the configuration of the image sensor 40 according to the third embodiment. FIG. 13 is a diagram illustrating the periphery of an AD converter (ADC) that performs A / D conversion on signals output from the pixels illustrated in FIG. 12. The image sensor 40 is provided with a PGA (Programmable Gain Amplifier) in front of the ADC for each pixel group with respect to the image sensor 30 shown in FIG. In the PGA, the amplification factor can be changed for each PD_ * constituting the pixel group. In the imaging device 40, the PGA amplifies the analog signals output from the pixel 200, the pixel 202, and the pixel 204, respectively, so that the dynamic range of the ADC can be used effectively.

  Further, the PGA may amplify the analog signals output from the pixel 200, the pixel 202, and the pixel 204 at different amplification factors. Thereby, even if the level of the analog signal is different for each RGB color, the dynamic range can be optimized for each color.

  FIG. 14 is a timing chart showing an operation for driving the image sensor 40. Similar to the CMOS linear sensor 10 shown in FIG. 2, for example, the timing control unit 14 generates a drive signal for the image sensor 40 using a reference clock (CLK). The image sensor 40 is provided with a PGA between the pixel group and the ADC, and an analog signal is transferred from Cdf to the PGA during a period when TS is High. The analog signal transferred to the PGA is amplified during a period when PGEN is High and is input to the ADC. The amplified analog signal input to the ADC is converted into a digital signal while ADEN is High.

(Fourth embodiment)
Next, an image sensor according to the fourth embodiment will be described. FIG. 15 is a diagram illustrating an outline of the configuration of the image sensor 45 according to the fourth embodiment. FIG. 16 is a diagram showing a configuration of the pixel shown in FIG. FIG. 17 is a diagram illustrating the periphery of an AD converter (ADC) that performs A / D conversion on signals output from the pixels illustrated in FIG. 15. The image sensor 45 is different from the image sensor 30 illustrated in FIG. 8 in that each pixel (each pixel 200, pixel 202, and pixel 204) includes an analog memory (mem_r) 210, an analog memory (mem_g) 212, and an analog memory (mem_b) 214. Are provided respectively. In addition to the functions of the timing control unit 14, the image sensor 45 includes a timing control unit (TG) 216 that performs control to store the output of each pixel in the analog memories 210, 212, and 214 for each pixel group. .

  FIG. 18 is a timing chart showing an operation for driving the image sensor 45. The timing control unit 216 generates a drive signal for driving each unit of the image sensor 45. In the imaging element 45, the analog memories 210, 212, and 214 store image signals output from the respective pixels (the respective pixels 200, 202, and 204) while the signal Sig_ST is set to High and the signal Mem_EN is set to High. That is, the image sensor 45 can store A_sig_r, A_sig_g, and A_sig_b in the analog memory under the control of the timing control unit 216, so that simultaneous exposure (global shutter) in which the exposure timings are matched in RGB is realized. That is, the same position (pixel) to be read can be read in each color at the same time, and color misregistration can be prevented.

(Comparative example)
Next, a comparative example of the image sensor will be described. FIG. 19 is a diagram showing an outline of the configuration of the CMOS area sensor 11 of the comparative example. In the CMOS area sensor 11, the pixels 200, the pixels 202, and the pixels 204 are arranged in a two-dimensional direction (main scanning direction and sub-scanning direction), for example, in a Bayer arrangement. The CMOS area sensor 11 is provided with an AD conversion unit (ADC) 110 for each column, for example. In FIG. 19, the CMOS area sensor 11 is shown focusing on pixels and processing circuits (ADC in this case) that are characteristically different between the CMOS linear sensor and the CMOS area sensor.

  In the CMOS area sensor 11, the information of one pixel read from the same position (pixel position of the reading target) in the reading target is one color of R, G, or B (1 pixel = 1 color). Information for the remaining two colors that are insufficient at one pixel at the same position (pixel position to be read) in the reading target is generated by performing interpolation processing from surrounding pixels and calculating.

  Therefore, even if the CMOS area sensor 11 shares a single ADC with a plurality of pixels (for example, pixels for each column) as one pixel group, interpolation processing is performed using values of peripheral pixels using different ADCs. Due to the difference in the characteristics of each ADC, color unevenness or false color occurs in the image. That is, the effect of each embodiment mentioned above is an effect peculiar to a CMOS linear sensor.

  Next, an image forming apparatus including an image reading apparatus having an image sensor according to the embodiment will be described. FIG. 20 is a diagram illustrating an outline of an image forming apparatus 50 including an image reading device 60 having, for example, an image sensor 45. The image forming apparatus 50 is, for example, a copying machine or an MFP (Multifunction Peripheral) having an image reading device 60 and an image forming unit 70.

  The image reading device 60 includes, for example, an image sensor 45, an LED driver (LED_DRV) 600, and an LED 602. The LED driver 600 drives the LED 602 in synchronization with a line synchronization signal output from the timing control unit (TG) 216. The LED 602 irradiates the original with light. The image sensor 45 receives reflected light from the document in synchronization with a line synchronization signal or the like, and a plurality of PD_ * (not shown) generate electric charges and start accumulation. The image sensor 45 outputs image data to the image forming unit 70 after performing AD conversion, parallel serial conversion, and the like.

  The image forming unit 70 includes a processing unit 80 and a printer engine 82, and the processing unit 80 and the printer engine 82 are connected via an interface (I / F) 84.

  The processing unit 80 includes an LVDS 800, an image processing unit 802, and a CPU 804. The CPU 804 controls each part of the image forming apparatus 50 such as the image sensor 45. In addition, the CPU 804 (or the timing control unit 216) performs control so that each PD_ * starts generating charges according to the amount of received light substantially simultaneously.

  The imaging element 45 outputs, for example, image data of an image read by the image reading device 60, a line synchronization signal, a transmission clock, and the like to the LVDS 800. The LVDS 800 converts received image data, a line synchronization signal, a transmission clock, and the like into parallel 10-bit data. The image processing unit 802 performs image processing using the converted 10-bit data, and outputs image data and the like to the printer engine 82. The printer engine 82 performs printing using the received image data.

  As described above, in the image pickup device according to the embodiment, the ADC that performs A / D conversion for each pixel group including a plurality of pixels is arranged in the vicinity of each pixel group. Therefore, the wiring resistance and wiring capacitance of the analog bus are reduced. It can be made small, and the speed of image reading can be increased. That is, the imaging device according to the embodiment can also reduce the driving frequency of the analog signal.

DESCRIPTION OF SYMBOLS 20 Image pick-up element 30 Image pick-up element 40 Image pick-up element 45 Image pick-up element 50 Image forming apparatus 60 Image reader 70 Image forming part 200 Pixel 202 Pixel 204 Pixel 206 Parallel serial conversion part 210 Analog memory (memory | storage part)
212 Analog memory (storage unit)
214 Analog memory (storage unit)
216 Timing control unit (control unit)
PD_ * Photodiode (photoelectric conversion element)
ADC AD converter PGA Amplifier

JP 2009-296544 A

Claims (9)

A plurality of photoelectric conversion elements;
An AD conversion unit that performs A / D conversion for each pixel group constituted by the plurality of photoelectric conversion elements selected among the plurality of photoelectric conversion elements;
Have
Each of the photoelectric conversion elements constituting the pixel group is connected to the AD converter corresponding to the pixel group by a bus line having a distance that can be transmitted within a predetermined time. A characteristic imaging device. The image sensor according to claim 1, wherein the photoelectric conversion elements are arranged in one direction for each color to receive light. The pixel group is:
The imaging device according to claim 2, wherein a plurality of pixels of the same color adjacent in the arrangement direction for each color are formed as one pixel group. The pixel group is:
The image sensor according to claim 2, wherein one pixel group is formed of pixels of different colors that can read a reading target at the same position in the arrangement direction for each color. The pixel group is:
One odd-numbered photoelectric conversion element in the arrangement direction of the photoelectric conversion elements of each color, and the arrangement direction of the photoelectric conversion elements of each color adjacent to the odd-numbered photoelectric conversion element in the arrangement direction The imaging device according to claim 2, wherein one pixel group is formed by one even-numbered photoelectric conversion device. The imaging device according to any one of claims 1 to 5, further comprising an amplifying unit that amplifies a signal in front of the AD conversion unit. The amplification unit is
The imaging device according to claim 6, wherein an amplification factor can be changed for each of the photoelectric conversion elements constituting the pixel group. An image reading apparatus comprising the image pickup device according to claim 1. An image reading apparatus according to claim 8,
An image forming apparatus comprising: an image forming unit that forms an image read by the image reading apparatus.

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