JP2015008362A - Imaging apparatus, image reader, image formation apparatus, and driving method of imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent crosstalk between respective pixels in an imaging apparatus.SOLUTION: Control of a read switch transistor SW is performed independently for each pixel of RGB. Consequently, voltage variation to other pixels due to the switching noise of clock feedthrough of a transistor can be reduced by capacitance division of a read transistor with parasitic capacitance in other pixels that are turned off at that time. Crosstalk between pixels can thereby be prevented. Furthermore, a switch transistor GSW is provided between the charge storage capacitors CRn, CSn of each pixel RGB and the ground GND. Consequently, voltage variation due to parasitic capacitance can be reduced. Even when the capacitance of each capacitor is reduced, leakage current can be prevented. Furthermore, when each capacitor has a small capacitance, the capacitor can be charged and discharged in a short time, and followability can be enhanced.

Description

  The present invention relates to an imaging apparatus, an image reading apparatus, an image forming apparatus, and a driving method of the imaging apparatus.

  Today, a batch exposure type imaging apparatus is known. This collective exposure type imaging apparatus exposes all pixels at once, and then reads out the reset voltage and the photoelectrically converted charges in order for each pixel accumulated in the capacitor. Then, CDS processing and A / D conversion processing are performed by the CDS circuit and A / D conversion circuit provided for each column and output. CDS is an abbreviation for “correlated double sampling”. A / D is an abbreviation for “Analog / Digital”.

  Patent Document 1 (Japanese Patent No. 4846076) discloses an amplification type solid-state imaging device for the purpose of obtaining a low-noise image signal. This amplification type solid-state imaging device includes a pixel array configured by arranging a plurality of pixels having a plurality of capacitors in a matrix, and a control circuit that performs operation control on each pixel constituting the pixel array. Each pixel includes a photoelectric conversion unit that generates and outputs a signal corresponding to received light, a first amplification transistor that amplifies and outputs a signal input to the gate from the photoelectric conversion unit, and a first amplification transistor And a reset transistor for resetting the gate voltage.

  In addition, the amplification type solid-state imaging device includes a plurality of capacitors for holding a signal output from the first amplification transistor to the first signal line, a plurality of capacitors corresponding to the plurality of capacitors, and the first signal line and the plurality of capacitors. And a plurality of capacitance switches each including one capacitor for performing input / output control between the first signal line and the plurality of capacitors. In addition, a second amplification transistor that amplifies a signal input to the gate from the first signal line and outputs the amplified signal to the second signal line, and a first signal line connected to the first signal line, And an initialization transistor that outputs to one signal line.

  Such an amplification type solid-state imaging device causes one of two capacitors in each pixel of the pixel array to perform a reset signal writing operation and the other to perform an optical signal writing operation. Thereafter, reading from each capacitor of each pixel to the gate of the second amplification transistor is sequentially performed, and all pixels are simultaneously and simultaneously written to each capacitor and sequentially read from each capacitor. At the time of reading, a third voltage is applied to the gate of the first amplification transistor to make it inactive, or an output switch provided between the first amplification transistor and the first signal line is turned off. As a result, it is possible to prevent inconvenience that the first amplifying transistor affects.

  Further, CDS processing is performed by taking a difference between the reset signal and the optical signal for each pixel read out sequentially. Thereby, it is possible to suppress fixed pattern noise caused by variations in threshold voltage in each of the first and second amplification transistors and reset noise to the gate of the first amplification transistor, and a low noise image. A signal can be obtained.

  However, the conventional batch exposure type imaging device such as the amplification type solid-state imaging device disclosed in Patent Document 1 has an image signal via a common output unit (CDS circuit, A / D conversion circuit, etc.) for each column. Therefore, there is the following problem with respect to the amount of charge read from the capacitor that has accumulated the charge.

  In other words, when the charge is read out from the target pixel unit, the change in the gate input signal of each transistor in the target pixel unit can enter other pixel units as charges via the parasitic capacitance of the transistors in the target pixel unit and other pixel units. There is sex. Due to this voltage variation, the original charge output level is not achieved, but crosstalk occurs between the pixel portions.

  In addition, when the previous pixel portion is at a low level, if the readout of the next pixel portion is at a high level, the potential fluctuation increases at the output portion, and if the responsiveness is not secured, the original level is detected. It becomes difficult. That is, depending on the level of the immediately preceding channel, crosstalk between pixel portions that deviates from the level that should be read out also occurs. Further, if the reading period is lengthened in order to detect the original output level, there arises a disadvantage that the operation speed becomes slow.

  SUMMARY An advantage of some aspects of the invention is that it provides an imaging apparatus, an image reading apparatus, an image forming apparatus, and a driving method of the imaging apparatus that can prevent crosstalk between pixel units. .

  In order to solve the above-described problems and achieve the object, the present invention provides a charge accumulation unit that accumulates charges according to incident light, a charge detection unit that detects charges accumulated in the charge accumulation unit, and a charge accumulation A plurality of pixel units each including at least a transfer transistor that transfers charge from the unit to the charge detection unit and a reset transistor that resets the charge detection unit, and a pixel that processes the charges from the pixel unit and sequentially transfers them to a subsequent circuit An output unit, a charge storage capacitor provided in the pixel output unit and configured to store charges detected by the charge detection unit, and a charge provided in the pixel output unit and detected by the charge detection unit are written into the charge storage capacitor. A plurality of write switch transistors for controlling the timing and the timing for reading the charge accumulated in the charge storage capacitor provided in the pixel output unit The cross-talk between the pixel unit and multiple connection switch transistors that are provided at the pixel output unit and control the charge input / output of the charge storage capacitor at the timing of writing and reading And a crosstalk prevention unit.

  According to the present invention, it is possible to prevent crosstalk between the pixel units.

FIG. 1 is a circuit diagram of a pixel portion of an imaging apparatus as a comparative example. FIG. 2 is a circuit diagram of a pixel output unit of an imaging apparatus as a comparative example. FIG. 3 is a block diagram illustrating a connection relationship among a pixel output unit, a post-processing unit, and a signal generation unit of an imaging apparatus as a comparative example. FIG. 4 is a timing chart of various signals of the imaging apparatus as a comparative example. FIG. 5 is a simplified circuit diagram of a pixel output unit of an imaging apparatus as a comparative example. FIG. 6 is an equivalent circuit diagram for explaining a source of clock feedthrough in an imaging apparatus as a comparative example. FIG. 7 is a circuit diagram of a pixel output unit of the imaging apparatus according to the first embodiment. FIG. 8 is a timing chart of various signals of the imaging apparatus according to the first embodiment. FIG. 9 is a simplified circuit diagram of the pixel output unit of the imaging apparatus according to the first embodiment. FIG. 10 is an equivalent circuit diagram for explaining that the number of clock feedthrough generation sources is reduced in the imaging apparatus according to the first embodiment. FIG. 11 is a circuit diagram of a pixel output unit of the imaging apparatus according to the second embodiment. FIG. 12 is a timing chart of various signals of the imaging apparatus according to the second embodiment. FIG. 13 is a diagram for explaining a noise canceling operation in the imaging apparatus according to the second embodiment. FIG. 14 is a simplified circuit diagram of the pixel output unit of the imaging apparatus according to the second embodiment. FIG. 15 is an equivalent circuit diagram for explaining that the number of clock feedthrough generation sources has decreased in the imaging apparatus according to the second embodiment. FIG. 16 is a cross-sectional view of an image reading apparatus according to the third embodiment. FIG. 17 is a cross-sectional view of the image forming apparatus according to the fourth embodiment.

  Hereinafter, embodiments of an imaging apparatus, an image reading apparatus, an image forming apparatus, and a driving method of the imaging apparatus will be described in detail with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a circuit diagram of a pixel unit R for R (red) of a batch exposure type imaging apparatus as a comparative example. The G (green) pixel portion G and the B (blue) pixel portion B have the same configuration. FIG. 2 is a circuit diagram of the pixel output unit 1 that writes, reads, and outputs signals from the pixel units R, G, and B in the batch exposure type imaging apparatus as a comparative example. The imaging device as the comparative example has a reset charge storage capacitor CRn and a signal charge storage capacitor CSn as charge storage capacitors. For this reason, as shown in FIG. 2, the imaging device as a comparative example includes a connection switch transistor CS_ * and a connection switch transistor CR_ * in addition to the write switch transistor SL (*: R, G, B). . The connection switch transistors CS_ * and CR_ * write the charges of the RGB pixel portions (channels) at a predetermined timing and read the charges of the signal charge storage capacitor CSn or the reset charge storage capacitor CRn. Control input and output.

  FIG. 3 is a block diagram illustrating a connection relationship between the pixel output unit 1, the post-processing unit 2, and the signal generation unit 3 of an imaging apparatus as a comparative example. Various control signals output from the signal generation unit 3 perform on / off control of each transistor having the same name. FIG. 4 is a timing chart showing timings of various signals from exposure to signal readout per time of an imaging apparatus as a comparative example having the pixel output unit 1 configured as shown in FIG.

  In FIG. 1, a light receiving element PD which is a charge storage unit is usually composed of an embedded light receiving element. The light receiving element PD generates a charge corresponding to the light received within the accumulation time. The floating diffusion region FD is reset to the power supply voltage Vdd which is the drain voltage of the reset transistor RT by the reset transistor RT before the signal charge is transferred from the light receiving element PD at time T80 in FIG. Alternatively, the floating diffusion region FD is reset to the source voltage of the corresponding reset transistor RT (not shown).

  Thereafter, at time T81 in FIG. 4, the writing switch transistor SL and the connection switch transistor CR_ * are turned on all at once. As a result, the reset charges in the floating diffusion region FD at the time of reset are transferred to the reset charge storage capacitor CRn (*) in FIG. 2 at the same time. Next, at time T82 in FIG. 4, the connection switch transistors CR_ * are turned off all at once, and the transfer transistor TX is turned on. As a result, the signal charge from the light receiving element PD is transferred to the floating diffusion region FD after the reset charge transfer.

  Next, at time T83 in FIG. 4, the transfer transistor TX is turned off, and the connection switch transistors CS_ * are turned on all at once and transferred to the signal charge storage capacitor CSn (*). Next, the connection switch transistors CS_ * are all turned off at the same time, and the batch writing of the charge storage capacitors CRn (*) and CSn (*) of the reset charge and the signal charge is completed.

  Next, at time T84 in FIG. 4, the read switch transistor SW is turned on, and at the same time, the connection switch transistor CR_R is turned on. As a result, the reset charge stored in the reset charge storage capacitor CRn (R) of the pixel unit R is transferred to the output terminal PIXOUTn of the pixel output unit 1. After the transfer, the connection switch transistor CR_R is turned off. Similarly, at time T85 in FIG. 4, the connection switch transistor CS_R is turned on and the signal stored in the signal charge storage capacitor CSn (R) of the pixel portion R is stored. The charge is transferred to the output terminal PIXOUTn of the pixel output unit 1. After the transfer, the connection switch transistor CS_R is turned off. In the next pixel portion G and pixel portion B, the same charge is stored for each charge stored in each charge storage capacitor (CRn (G), CSn (G), CRn (B), CSn (B)). Processing is performed (time T86, T87 in FIG. 4).

  As described above, the electric charge of the output terminal PIXOUTn varies in the order of the readout pixel portion from time T80 to T87 in FIG. 4 (R reset charge → R signal charge → G reset charge → G signal charge → B reset charge → B signal charge). During this readout period, the readout switch transistor SW is common to all the pixel units, and the readout switch transistors SW other than the readout pixel unit are also turned on. This is because the charge reading is finally controlled by turning on the connection switch transistors CR_ * and CS_ *. Therefore, in the case of a pixel portion that does not perform readout, even if the readout switch transistor SW is on, readout of reset charge or signal charge is not performed if the connection switch transistors CR_ * and CS_ * are off.

  By the way, each of the above-described transistors is a semiconductor such as a negative-channel metal oxide semiconductor (nMOS), and therefore includes various factors that generate noise when turned on and off. For example, charge injection is a phenomenon in which, when a transistor (switching element) is on, charges (electrons or holes) that form a pixel portion are turned off, so that the transistor moves to the source or drain of the transistor. In addition, clock feedthrough affects the potential due to the electrostatic effect due to the parasitic capacitance between the gate and the drain or between the gate and the source as the gate potential changes from on to off or from off to on. It is a phenomenon.

  In particular, the clock feedthrough hinders the high speed because it depends on the change speed of the gate input of the transistor, that is, the operation speed of the imaging device. For this reason, the generated charge affects the pixel portion to be read later, and the charge is transmitted to the output terminal PIXOUTn as much as that, and as a result, crosstalk occurs between the pixel portions.

  FIG. 5 shows a simplified circuit diagram of the pixel output unit 1 in order to explain the phenomenon of clock feedthrough. For example, when the charge of the reset charge storage capacitor CRn (R) is read by turning on the connection switch transistor CR_R and the read switch transistor SW, all charges are read out. However, due to the clock feedthrough described above, the change in gate voltage is also output through the parasitic capacitance of each transistor. The charge due to the change is transmitted to the output terminal PIXOUTn, the pixel unit G, and the pixel unit B at a rate that changes depending on the circuit configuration. In this example, for the sake of easy understanding, it is assumed that all of this charge flows into the reset charge storage capacitor CRn (G) of the next pixel unit G. That is, the solid-line arrows in FIG. 5 are normal charges output from the reset charge storage capacitor CRn (R) during reading, and the dotted-line arrows are charges due to noise that wraps around through the parasitic capacitance.

  In the case of an imaging device as a comparative example, as shown in FIGS. 4 and 5, the charge of the reset charge storage capacitor CRn (R) is read by turning on the connection switch transistor CR_R and the read switch transistor SW. For this reason, as shown in FIG. 5, there are a total of three clock feedthrough generation sources including two read switch transistors SW and one connection switch transistor CR_R. At this time, the connection switch transistor CR_G is off, but a parasitic capacitance is formed by the capacitance formed by the inversion layer between the drain and the source. These things are represented by an equivalent circuit as shown in FIG. For example, the change in voltage of the signal charge storage capacitor CSn (G) of the pixel portion G due to noise is ΔVc1, each parasitic capacitance value of the equivalent circuit of FIG. 6 is C, and the capacitance value of the reset charge storage capacitor CRn (G). Is 10C. In this case, “ΔVc1 = 0.070C” due to the capacity partial pressure. Therefore, after that, when the pixel portion G is read, the charge corresponding to the change is also output to the output terminal PIXOUTn.

  In the configuration of this example, the charge storage capacitor is divided into a signal charge storage capacitor CSn and a reset charge storage capacitor CRn. Even in this case, if the amount of change applied to each of the charge storage capacitors CSn and CRn of the pixel unit G is not uniform, the difference calculation is performed in the CDS circuit (correlated double sampling circuit) 11 of the post-processing unit 2 in FIG. This will affect the final output value. The same phenomenon occurs for the pixel portion B even when the pixel portion G is read. Therefore, the final output terminal PIXOUTn outputs a value deviated from the original output level (dotted line waveform) as the reset voltage of the pixel portions G and B, as shown by the solid lines at times T86 and T87 in FIG. End up.

  On the other hand, the speed of potential change at the output terminal PIXOUTn depends on the capacitance values of the charge storage capacitors CRn (*) and CSn (*). Note that when a voltage is applied to each of the charge storage capacitors CRn (*) and CSn (*), a slight leakage current is generated. For this reason, it is necessary to set the capacitance values of the charge storage capacitors CRn (*) and CSn (*) so that the influence can be ignored.

  However, when the capacitance values of the charge storage capacitors CRn (*) and CSn (*) are increased, the influence of the leakage current is reduced. However, regarding the potential fluctuation of the output terminal PIXOUTn, the charge storage capacitor CRn (* ), The discharge speed of CSn (*) is slow. If the on-time of the connection switch transistors CR_ * and CS_ * is shortened in order to increase the discharge speed of the charge storage capacitors CRn (*) and CSn (*), the following problems occur. In this case, all charges stored in the charge storage capacitors CRn (*) and CSn (*) remain without being discharged, and a value deviating from the original output level is output. The dotted line waveform and solid line waveform at the output terminal PIXOUTn in FIG. 4 indicate the light output in each of the R and B pixel portions (the potential decreases because the potential of the floating diffusion region FD decreases in proportion to the amount of charge). Each waveform in the case of is shown. Such a problem becomes more prominent when the charge is read, as the difference in charge amount between the previous channel (the pixel portion that has been read before) and the next channel (the pixel portion that has been read next) is larger. .

  In this case, after the signal charge is read out, the reset charge of the next pixel portion is read out. On the same principle, analog / digital conversion is performed by the ADC circuit 10 and the CDS circuit 11 performs CDS in the post-processing unit 2 in FIG. The final signal level output is affected by processing. ADC is an abbreviation for analog / digital conversion. As a result, when the relationship between the preceding and following pixel portions (pixel portions adjacent in the readout order) is a color, the next level is given to the level of the previous color, and crosstalk between colors is generated as an output of the imaging device. If the time for turning on the readout switch transistor SW is secured long enough to sufficiently discharge electric charges, crosstalk between colors can be prevented. However, it is difficult to drive the imaging device at high speed by securing the discharge time of the charge.

  For this reason, the imaging apparatus according to the first embodiment has a configuration in which the readout switch transistor SW_ * (*: R, G, B) is controlled independently for each pixel unit as an example of the crosstalk prevention unit. Have. FIG. 7 is a block diagram of the pixel output unit 1 of the imaging apparatus according to the first embodiment. FIG. 8 shows a timing chart of various signals of the imaging apparatus according to the first embodiment.

  In FIG. 8, the imaging device of the first embodiment performs batch writing of the charge storage capacitors CRn and CSn for reset charge and signal charge from time T80 to time T83, as in the imaging device of the comparative example described above. To implement. The floating diffusion region FD is an example of a charge detection unit. Next, in the imaging device of the first embodiment, the readout switch transistors SW_R, SW_G, and SW_B are controlled independently.

  First, the signal generator 3 shown in FIG. 3 turns on the read switch transistor SW_R during the time T84 to the time T86 in FIG. At time T84 during this period, the signal generator 3 turns on the connection switch transistor CR_R. As a result, the reset charge stored in the reset charge storage capacitor CRn (R) of the pixel unit R is transferred to the output terminal PIXOUTn of the pixel output unit 1.

  After the transfer of the reset charge, the signal generator 3 turns off the connection switch transistor CR_R, and similarly turns on the connection switch transistor CS_R at time T85 in FIG. As a result, the signal charge stored in the signal charge storage capacitor CSn (R) of the pixel unit R is transferred to the output terminal PIXOUTn of the pixel output unit 1. After the transfer, the signal generator 3 turns off the connection switch transistor CS_R.

  Similarly, in the case of the pixel portion G, the signal generator 3 turns on the read switch transistor SW_G during the time T86 to T88 in FIG. 8, and turns on the connection switch transistor CR_G at the time T86 during this time. As a result, the reset charge stored in the reset charge storage capacitor CRn (G) of the pixel unit G is transferred to the output terminal PIXOUTn of the pixel output unit 1. The signal generator 3 turns on the connection switch transistor CS_G at time T87 between times T86 and T88 in FIG. As a result, the signal charge stored in the signal charge storage capacitor CSn (G) of the pixel unit G is transferred to the output terminal PIXOUTn of the pixel output unit 1.

  Similarly, in the case of the pixel portion B, the signal generating portion 3 turns on the read switch transistor SW_B during the time T88 to T90 in FIG. 8, and turns on the connection switch transistor CR_B at the time T88 during this time. As a result, the reset charge stored in the reset charge storage capacitor CRn (B) of the pixel unit B is transferred to the output terminal PIXOUTn of the pixel output unit 1. The signal generator 3 turns on the connection switch transistor CS_B at time T89 between times T88 and T90 in FIG. As a result, the signal charge stored in the signal charge storage capacitor CSn (B) of the pixel unit G is transferred to the output terminal PIXOUTn of the pixel output unit 1.

  Next, FIG. 9 shows a simplified circuit diagram of the pixel output unit 1 of the imaging apparatus according to the first embodiment. Similar to FIG. 5, the influence on the pixel portion G when the pixel portion R is read will be described. When the charge of the signal charge storage capacitor CRn (R) is read by turning on the connection switch transistor CR_R and the readout switch transistor SW_R, all the charges are read out, but at this time, the readout switch transistor SW_G is off. Can be regarded as a parasitic capacitance between the drain and the source. For this reason, the clock feedthrough generation source can be a total of two locations of the connection switch transistor CR_R and the read switch transistor SW_R. In this case, the equivalent circuit is as shown in FIG.

  Actually, if the change in the voltage of the signal charge storage capacitor CSn (G) of the pixel portion G due to this noise is ΔVc2, it becomes “ΔVc2 = 0.038C” due to the capacitance division, and the change in the conventional configuration It is greatly reduced from ΔVc1 = 0.070C. As a result, it is possible to reduce the amount of crosstalk with respect to the output when the pixel portion G is subsequently read out.

  As is apparent from the above description, the imaging apparatus according to the first embodiment controls the read switch transistor SW_ * (*: R, G, B) independently for each pixel unit. As a result, the voltage fluctuation to the other pixel portion due to the switching noise of the clock feedthrough of the transistor can be reduced by dividing the capacitance by the parasitic capacitance of the readout transistor (off) of the other pixel portion. For this reason, crosstalk between pixel portions can be prevented.

(Second Embodiment)
Next, an imaging apparatus according to the second embodiment will be described. FIG. 11 is a circuit diagram of the pixel output unit 1 of the batch exposure type imaging apparatus according to the second embodiment. FIG. 12 is a timing chart of various signals from exposure to signal readout of the imaging apparatus according to the second embodiment. As an example of the crosstalk prevention unit, the imaging apparatus according to the second embodiment has the following configuration in addition to the configuration in which the control of the readout switch transistor SW is controlled independently for each pixel unit in each pixel unit RGB. That is, this imaging device has a configuration in which the switch transistor GSW_ * is provided between the charge storage capacitors CRn (*) and CSn (*) and the ground GND in each pixel portion RGB.

  In the case of the imaging apparatus according to the first embodiment described above, it is difficult to prevent crosstalk between pixel units due to insufficient responsiveness. On the other hand, the image pickup apparatus according to the second embodiment prevents crosstalk due to insufficient response as well as crosstalk due to parasitic capacitance of the transistor, as will be described below.

  That is, in the imaging device according to the second embodiment, the signal generator 3 turns on the reset transistor RT before the signal charge is transferred from the light receiving element PD at time T120 in FIG. As a result, the floating diffusion region FD is reset to the power supply voltage Vdd that is the drain voltage of the reset transistor RT or the source voltage of the reset transistor RT corresponding thereto. Thereafter, the signal generating unit 3 turns on the write switch transistor SL, the connection switch transistor CR_ *, and the switch transistor GSW_ * at time T121 in FIG. As a result, the reset charges in the floating diffusion region FD at the time of resetting are transferred to all the pixels all at once to the reset charge storage capacitor CRn (*).

  As described above, generally, a MOS switch generates switching noise such as charge injection and clock feedthrough when it is turned on and off. However, in the imaging device of the second embodiment, as shown in FIG. 13, the connection switch transistor CR_ * and the switch transistor GSW_ * are simultaneously turned on. Therefore, the potential difference between both ends of the reset charge storage capacitor CRn (*) does not change, noise can be canceled out, and output linearity deterioration and the like can be prevented.

  In the case of the imaging device of the second embodiment, the capacitance values of the reset charge storage capacitor CRn (*) and the signal charge storage capacitor CSn (*) described later are smaller than those of the imaging device of the comparative example. It is a capacity value. For this reason, the reset charge storage capacitor CRn (*) and the signal charge storage capacitor CSn (*) store charges in the same manner as the imaging device of the comparative example described above, but the capacitance value is small. Charging speed is getting faster.

  Next, the signal generator 3 turns off the connection switch transistor CRn_ * and the switch transistor GSW_ * at time T122 in FIG. 12, and turns on the transfer transistor TX as in the imaging device of the comparative example. As a result, the signal charge from the light receiving element PD is transferred to the floating diffusion region FD after the reset charge transfer.

  Next, at time T123 in FIG. 12, the signal generator 3 turns off the transfer transistor TX, turns on the connection switch transistor CS_ * and the switch transistor GSW_ * at the same time, and sets the signal charge storage capacitor CSn (*). Transfer signal charge.

  Next, the signal generator 3 simultaneously turns off the connection switch transistor CS_ * and the switch transistor GSW_ * and turns off the write switch transistor SL at time T124 in FIG. Thus, the batch writing of the reset charge and signal charge capacitors CRn (*) and CSn (*) is completed.

  Next, the signal generator 3 turns on the read switch transistor SW_R during the time T125 to T126 in FIG. Further, the signal generator 3 simultaneously turns on the connection switch transistor CR_R and the switch transistor GSW_R at time T125 while the read switch transistor SW_R is on. Thereby, at time T125, the reset charge stored in the reset charge storage capacitor CRn (R) of the pixel unit R is transferred to the output terminal PIXOUTn of the pixel output unit 1. Also at this time, since the connection switch transistor CR_R and the switch transistor GSW_R are simultaneously turned on, the potential difference between both ends of the reset charge storage capacitor CRn (R) does not change, and noise can be canceled as shown in FIG. .

  Next, the signal generator 3 simultaneously turns off the connection switch transistor CR_R and the switch transistor GSW_R. Further, the signal generator 3 simultaneously turns on the connection switch transistor CS_R and the switch transistor GSW_R at time T126 while the read switch transistor SW_R is on. Thereby, at time T126, the signal charge stored in the signal charge storage capacitor CSn (R) of the pixel unit R is transferred to the output terminal PIXOUTn of the pixel output unit 1. After the transfer, the signal generator 3 turns off the connection switch transistor CS_R and the switch transistor GSW_R at the same time.

  Next, the signal generator 3 turns on the read switch transistor SW_G during the time T127 to T128 in FIG. Further, the signal generating unit 3 simultaneously turns on the connection switch transistor CR_G and the switch transistor GSW_G at time T127 while the read switch transistor SW_G is on. Thereby, at time T127, the reset charge stored in the reset charge storage capacitor CRn (G) of the pixel unit G is transferred to the output terminal PIXOUTn of the pixel output unit 1. Also at this time, since the connection switch transistor CR_G and the switch transistor GSW_G are simultaneously turned on, the potential difference between both ends of the reset charge storage capacitor CRn (G) does not change, and noise can be canceled as shown in FIG. .

  Next, the signal generator 3 simultaneously turns off the connection switch transistor CR_G and the switch transistor GSW_G. Further, the signal generator 3 simultaneously turns on the connection switch transistor CS_G and the switch transistor GSW_G at time T128 while the read switch transistor SW_G is on. Thereby, at time T128, the signal charge stored in the signal charge storage capacitor CSn (G) of the pixel unit G is transferred to the output terminal PIXOUTn of the pixel output unit 1. After the transfer, the signal generation unit 3 turns off the connection switch transistor CS_G and the switch transistor GSW_G at the same time.

  Next, the signal generator 3 turns on the read switch transistor SW_B during the time T129 to T130 in FIG. Further, the signal generator 3 simultaneously turns on the connection switch transistor CR_B and the switch transistor GSW_B at time T129 while the read switch transistor SW_B is on. Thereby, at time T129, the reset charge stored in the reset charge storage capacitor CRn (B) of the pixel unit B is transferred to the output terminal PIXOUTn of the pixel output unit 1. Also at this time, since the connection switch transistor CR_B and the switch transistor GSW_B are simultaneously turned on, the potential difference between both ends of the reset charge storage capacitor CRn (B) does not change, and noise can be canceled as shown in FIG. .

  Next, the signal generator 3 simultaneously turns off the connection switch transistor CR_B and the switch transistor GSW_B. Further, the signal generating unit 3 simultaneously turns on the connection switch transistor CS_B and the switch transistor GSW_B at time T130 while the read switch transistor SW_B is on. Thereby, at time T130, the signal charge stored in the signal charge storage capacitor CSn (B) of the pixel unit B is transferred to the output terminal PIXOUTn of the pixel output unit 1. After the transfer, the signal generator 3 turns off the connection switch transistor CS_B and the switch transistor GSW_B at the same time.

  Next, crosstalk caused by parasitic capacitance of a transistor will be described with reference to a simplified circuit diagram of the pixel output unit 1 shown in FIG. Note that the influence on the pixel portion G when the pixel portion R is read will be described. When the charge of the reset charge storage capacitor CRn (R) is read by turning on the connection switch transistor CR_R, the switch transistor GSW_R, and the read switch transistor SW_R, all charges are read out. At this time, since the read switch transistor SW_G and the switch transistor GSW_G are off, they can be regarded as a parasitic capacitance between the drain and the source. Therefore, there are two clock feedthrough generation sources, and an equivalent circuit is as shown in FIG.

  Actually, if the change in the voltage of the signal charge storage capacitor CSn (G) of the pixel portion G due to this noise is ΔVc3, “ΔVc3 = 0.028C” due to the capacitance division, and the change in the imaging device of the comparative example As seen from “ΔVc1 = 0.070C” of the minute, it is greatly reduced. For this reason, it is possible to reduce the amount of crosstalk with respect to the output when the pixel portion G is subsequently read out.

  Next, the signal generator 3 turns off all the switch transistors GSW_ * between the charge storage capacitors CRn (*) and CSn (*) and the ground GND in the charge holding period other than writing and reading. . As a result, leakage current can be prevented, and the capacitance values of the charge storage capacitors CRn (*) and CSn (*) are made smaller than those of the imaging device of the comparative example (CRn (*), CSn (*) has the same capacitance value). For this reason, compared with the imaging device of the comparative example, the potential fluctuation speed can be increased without increasing the leakage current. Therefore, even if the ON period of the connection switch transistors CR_ * and CS_ * is not lengthened, a signal of a voltage corresponding to the amount of charge accumulated in each of the charge storage capacitors CRn (*) and CSn (*) within the period. Can be output. Then, even if a sudden change in output level occurs between the pixel portions, it can be dealt with.

  As is apparent from the above description, the image pickup apparatus according to the second embodiment independently controls the readout switch transistor SW for each pixel unit RGB in each pixel unit RGB. At the same time, in each pixel portion RGB, a switch transistor GSW_ * is provided between each charge storage capacitor CRn (*), CSn (*) and the ground GND. The switch transistors GSW_ * between the charge storage capacitors CRn (*) and CSn (*) and the ground GND are all turned off during the charge holding period other than writing and reading.

  As a result, leakage current can be prevented, and the capacitance values of the charge storage capacitors CRn (*) and CSn (*) can be reduced. For this reason, the speed of potential fluctuation can be increased without increasing the leakage current. Therefore, even if the ON period of the connection switch transistors CR_ * and CS_ * is not lengthened, a signal of a voltage corresponding to the amount of charge accumulated in each of the charge storage capacitors CRn (*) and CSn (*) within the period. Can be output. For this reason, even when there is a sudden change in the output level between the pixel portions, it is possible to cope with this (followability can be improved).

  In the description of the second embodiment, the charge storage capacitors CRn (*) and CSn (*) are connected to the ground GND. However, a predetermined voltage other than the ground GND (a voltage equal to or lower than Vdd) is used. It is possible to obtain the same effect as described above even if it is connected to (preferably).

  In the description of the second embodiment, the case where the pixel portions are between colors has been described. However, the same principle is applied to the overall interference between the pixel portions in the same column even if it is not a color. An effect can be obtained.

(Third embodiment)
Next, an image reading apparatus according to a third embodiment to which the above-described imaging apparatus is applied will be described. FIG. 16 is a schematic cross-sectional view illustrating a configuration example of a mechanism unit of the image reading apparatus according to the third embodiment. In FIG. 16, an image reading apparatus 100 is a scanner apparatus or a single scanner apparatus provided in an image forming apparatus such as a digital copying machine, a digital multifunction peripheral, or a facsimile machine, and is one of those described in the above embodiments. The imaging device is provided.

  The image reading apparatus 100 includes a contact glass 101 on which an original is placed. The image reading apparatus 100 further includes a first carriage 106 including a light source 102 for document exposure and a first reflection mirror 103, and a second carriage 107 including a second reflection mirror 104 and a third reflection mirror 105. Yes.

  In addition, the image reading apparatus 100 includes a lens unit 108 for forming an image of the light reflected by the third reflecting mirror 105 on the light receiving region (imaging element) of the imaging device 109. Further, the image reading apparatus 100 also includes a reference member 110 having a reference density such as a reference white plate used for various distortion corrections by a reading optical system and the like, and a sheet through reading slit 111.

  The reference member 110 can be illuminated by the light source 102, and is provided at a position different from the contact glass 101 and the sheet-through reading slit 111 serving as a document illumination position. With respect to the imaging device 109, the reflected light from any of the document placed on the contact glass 101 or the document passing through the sheet-through reading slit 111 and the reference member 110 can be incident light.

  An automatic document feeder (hereinafter abbreviated as “ADF”) 200, which is an automatic document feeder, is provided above the image reading apparatus 100 so that the ADF 200 can be opened and closed with respect to the contact glass 101. Are connected via a hinge or the like (not shown). The ADF 200 includes a document tray 201 as a document placing table on which a document bundle composed of a plurality of documents can be placed. The ADF 200 also separates and feeds documents one by one from a bundle of documents placed on the document tray 201 and automatically feeds them toward the sheet-through reading slit 111. Means are also provided.

  In the image reading apparatus 100 configured as described above, an operation in a scan mode in which an image surface of a document placed on the contact glass 101 is scanned (scanned) and an image of the document is read will be described. In the scan mode, the first carriage 106 and the second carriage 107 are moved in the arrow A direction (sub-scanning direction) by a stepping motor (not shown) to scan the document. At this time, the second carriage 107 moves at a speed half that of the first carriage 106 in order to maintain a constant optical path length from the contact glass 101 to the light receiving region (imaging device) of the imaging device 109.

  At the same time, an image surface that is the lower surface of the document set on the contact glass 101 is illuminated (exposed) by the light source 102 of the first carriage 106. Then, the reflected light from the image plane is sequentially reflected by the first reflecting mirror 103 of the first carriage 106, the second reflecting mirror 104 of the second carriage 107, and the third reflecting mirror 105. Then, the light flux reflected by the third reflecting mirror 105 is converged by the lens unit 108 and imaged on the light receiving region (imaging device) of the imaging device 109.

  The imaging device 109 generates an analog electric signal obtained by photoelectrically converting the amount of light received by each pixel for each line by the imaging element in the light receiving region. The electric signal is converted into a digital signal by each unit in the imaging device 109 and amplified with the adjusted gain, and the image of the original is read and output as image data.

  Next, the operation of the sheet through mode in which an original is automatically fed by the ADF 200 and an image of the moving original is read will be described. In the sheet through mode, the first carriage 106 and the second carriage 107 move to the lower side of the sheet through reading slit 111 and stop. Thereafter, the feeding roller 202 automatically feeds the document in the direction indicated by the arrow B (sub-scanning direction) sequentially from the lowermost document placed on the document tray 201, and the position of the sheet through reading slit 111 is adjusted. As it passes, the document is scanned.

  At this time, the lower surface (image surface) of the automatically fed document is illuminated by the light source 102 of the first carriage 106. Then, the reflected light from the image plane is sequentially reflected by the first reflecting mirror 103 of the first carriage 106, the second reflecting mirror 104 of the second carriage 107, and the third reflecting mirror 105. Then, the reflected light beam from the third reflecting mirror 105 is focused by the lens unit 108 and imaged on the imaging device 109.

  The imaging device 109 outputs an analog electrical signal obtained by photoelectrically converting the amount of light received by each pixel for each line by the imaging device in the light receiving region. The electrical signal is converted into a digital signal by each unit in the imaging device 109 and amplified with the adjusted gain as described above, and is output as image data obtained by reading a document image. The document whose image has been read in this way is discharged to a discharge port (not shown).

  Note that an image obtained by reflected light from the reference member 110 that is illuminated by the light source 102 that has been lit is read by the imaging device 109 before the image is read in the scan mode or the sheet-through mode. Then, shading correction data is generated and stored in the imaging device 109 so that the level of each pixel of the image data for one line is a uniform predetermined level. Thereafter, when reading the image of the document, shading correction is performed on the image data read by the imaging device 109 based on the previously stored shading correction data.

  Further, when the ADF 200 is provided with a conveyance belt, the document can be automatically fed to the reading position on the contact glass 101 by the ADF 200 and the image of the document can be read even in the scan mode. Therefore, even if the target document reads a document having a density difference between RGB, crosstalk between colors can be suppressed and a high-quality image can be acquired.

(Fourth embodiment)
Next, image formation according to the fourth embodiment to which any of the imaging devices described in the first and second embodiments and the image reading device described in the third embodiment are applied. The device will be described. FIG. 17 is a schematic cross-sectional view illustrating a configuration example of a mechanism unit of the image forming apparatus according to the fourth embodiment.

  This image forming apparatus 300 is provided with the image reading apparatus 100 described in the third embodiment. 17, the same parts as those in FIG. 16 are denoted by the same reference numerals. However, the ADF 400 provided on the image reading apparatus 100 is somewhat different from the ADF 200 shown in FIG.

  The image forming apparatus 300 is a digital copying machine provided with the image reading apparatus 100. An automatic document feeder (ADF) 400 is provided above the contact glass 101 on which the document of the image reading apparatus 100 is placed. The ADF 400 is connected to a contact glass 101 of the image reading apparatus 100 by a hinge or the like (not shown) so that the ADF 400 can be opened and closed.

  The ADF 400 includes a document tray 401 as a document placement table on which a document bundle composed of a plurality of documents can be placed. The ADF 400 automatically feeds documents one by one from a bundle of documents placed on the document tray 401 with the image side up by pressing a print key on an operation unit (not shown). In order to convey the document toward the sheet-through reading slit 111 or the contact glass 101, the ADF 400 also includes separation / feeding means including a feeding roller 402 and a conveying belt 403. The original fed by the feed roller 402 or the transport belt 403 is read out and then discharged onto the upper surface of the ADF 400 by the transport belt 403 and the discharge roller 404.

  Here, the operation of the controller (not shown) and the ADF 400 when the document is conveyed to the reading position of the contact glass 101 by the ADF 400 will be described. The feed motor of the ADF 400 is driven by an output signal from the controller. When the feed start signal generated by pressing the print key on the operation unit is input, the controller turns on the feed motor. It is designed to drive forward / reverse.

  When the feed motor is driven in the forward direction, the feed roller 402 rotates clockwise to automatically feed the document located at the uppermost position from the bundle of documents on the document tray 401, and the sheet through reading slit 111 or It is conveyed toward the contact glass 101. When the trailing edge of the document is detected by the document set detection sensor 405, the controller drives the feed motor in reverse based on the output signal from the document set detection sensor 405. This prevents subsequent documents from entering.

  When the document set detection sensor 405 detects the trailing edge of the document, the controller counts a rotation pulse of a conveyance belt motor (not shown) from this detection time point, and when the rotation pulse reaches a predetermined value, the conveyance belt The drive of 403 is stopped. By stopping the conveyance belt 403, the document is stopped at the reading position on the contact glass 101.

  Further, when the trailing edge of the document is detected by the document set detection sensor 405, the feeding motor is driven to rotate forward again, and the subsequent document is separated and automatically fed as described above. Then, the sheet is conveyed toward the contact glass 101, and when the pulse of the feeding motor from the time when the document is detected by the document set detection sensor 405 reaches a predetermined pulse, the feeding motor is stopped and the next document is detected. To wait first.

  When the document stops at the reading position on the contact glass 101, the image of the document is read. When this image reading is completed, a signal indicating that is input to the controller, so that the controller drives the conveyor belt motor to rotate forward by that signal, and the document is discharged from the contact glass 101 by the conveyor belt 403. It is carried out toward the roller 404.

  As described above, the original bundle placed on the original tray 401 of the ADF 400 is automatically fed from the uppermost original by pressing the print key, and the image plane is placed at the reading position on the contact glass 101. It is conveyed with the face down. The document that has been conveyed to the reading position and stopped is read out from the discharge port by the conveying belt 403 or the like after the image is read. When it is detected that there is a next document on the document tray 401, the next document is automatically fed and conveyed onto the contact glass 101 in the same manner as the previous document.

  On the other hand, a first tray 301, a second tray 302, and a third tray 303, which are paper feed trays, are provided in the lower part of the image forming apparatus 300. The transfer paper (recording medium) loaded on each paper feed tray is fed by a first paper feed unit 311, a second paper feed unit 312, and a third paper feed unit 313, respectively. Then, the transfer paper is conveyed to a position where it comes into contact with a drum-shaped photosensitive member (photosensitive drum) 315 as an image carrier by a vertical conveying unit 314. Actually, any one of the trays 301 to 303 is selected, and the transfer paper is fed therefrom. Also, a recording medium other than transfer paper can be used.

  Image data read by the image reading apparatus 100 is temporarily stored in an image memory (not shown). Then, the laser light generated in the writing unit 350 is modulated by the image data, and the surface of the photoconductor 315 charged in advance by the charging unit (not shown) is exposed by the laser light, and electrostatic in accordance with the image data is exposed. A latent image is formed. The surface of the photoreceptor 315 on which the electrostatic latent image is formed passes through the developing unit 327, so that a toner image developed with toner is formed.

  The transfer sheet, which is a recording medium fed from the selected paper feed tray, is transferred by the transfer belt 316 at the same speed as the rotation of the photoconductor 315, and the toner image on the photoconductor 315 is transferred. The transfer sheet is conveyed to a fixing unit 317, where the toner image is fixed, and then discharged by a discharge unit 318 to a discharge tray 319 outside the apparatus.

  Here, the function of the paper discharge unit 318 will be described. For example, if you want to reverse a transfer paper with a toner image on one side for face down (image side down to align the transfer paper in page order), the transfer paper with the image Then, the paper is conveyed to the double-sided input conveyance path 320 by the paper discharge unit 318. Then, after the switchback is reversed by the reversing unit 321, the paper is discharged to the paper discharge tray 319 through the reverse paper discharge conveyance path 322. When images are formed on both sides of the transfer paper, the transfer paper on which the image is formed on one side is conveyed to the double-sided input conveyance path 320 by the paper discharge unit 318 and is switched back by the reverse unit 321. After that, it is sent to the duplex conveying unit 323.

  The transfer paper sent to the double-sided conveyance unit 323 is fed again from the double-sided conveyance unit 323 in order to transfer the toner image formed on the photoconductor 315 again, and is again transferred to the photoconductor 315 by the vertical conveyance unit 314. It is conveyed to the position where it abuts. Then, after the toner image is transferred to the other surface, the toner image is fixed by the fixing unit 317 and discharged to the paper discharge tray 319 by the paper discharge unit 318.

  The photoconductor 315, the conveyance belt 316, the fixing unit 317, the paper discharge unit 318, and the development unit 327 are driven by a main motor (not shown), and the driving power of the main motor is transmitted to each paper feed unit 311 to 313 by a paper feed clutch. To be driven. The vertical conveyance unit 314 is driven by the driving force of its main motor being transmitted via an intermediate clutch.

  The writing unit 350 includes a laser output unit 351, an imaging lens 352, and a mirror 353. The laser output unit 351 includes a laser diode that is a laser light source and a rotating polygon mirror (polygon mirror) or a vibrating mirror that scans the laser beam. The laser light emitted from the laser output unit 351 is deflected by a polygon mirror or a vibrating mirror, passes through an imaging lens 352, is folded by a mirror 353, and is focused on the surface of the photoreceptor 315.

  The image forming apparatus according to the fourth embodiment shown in FIG. 17 includes the image reading apparatus according to the third embodiment shown in FIG. Crosstalk can be reduced and high-quality images can be printed.

  Each above-mentioned embodiment is shown as an example and is not intending limiting the range of the present invention. Each of the novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. Each embodiment and modifications of each embodiment are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Pixel output part 2 Subsequent process part 3 Signal generation part 10 ADC circuit (analog / digital conversion circuit)
11 CDS circuit (correlated double sampling circuit)
Vdd power supply voltage RT reset transistor TX transfer transistor FD floating diffusion region PD light receiving element CS_ * connection switch transistor CSn (*) signal charge storage capacitor CR_ * connection switch transistor CRn (*) reset charge storage capacitor SL write switch transistor SW read Switch transistor PIXOUTn Output terminal GSW_ * Switch transistor

Japanese Patent No. 4846076

Claims (9)

A charge accumulator that accumulates charges according to incident light; a charge detector that detects charges accumulated in the charge accumulator; a transfer transistor that transfers charges from the charge accumulator to the charge detector; and A plurality of pixel units including at least a reset transistor for resetting the charge detection unit;
A pixel output unit that processes charges from the pixel unit and sequentially transfers them to a subsequent circuit;
A charge storage capacitor provided in the pixel output unit for storing the charge detected by the charge detection unit;
A plurality of write switch transistors provided in the pixel output unit for controlling the timing of writing the charge detected by the charge detection unit into the charge storage capacitor;
A plurality of readout switch transistors provided in the pixel output section for controlling the timing of reading out the charges accumulated in the charge accumulation capacitor;
A plurality of connection switch transistors that are provided in the pixel output unit and that control charge input / output of the charge storage capacitor at the timing of writing and reading;
An imaging apparatus comprising: a crosstalk prevention unit that prevents crosstalk between the pixel units. The imaging apparatus according to claim 1, wherein the crosstalk prevention unit prevents the crosstalk by controlling the readout switch transistor independently of each pixel unit. The imaging apparatus according to claim 1, wherein the crosstalk prevention unit includes a switch transistor that connects the charge storage capacitor to a predetermined potential. The imaging apparatus according to claim 3, further comprising on / off control means for performing on / off control of the connection switch transistor and the switch transistor at the time of writing at a timing of canceling switching noise. The imaging apparatus according to claim 4, wherein the on / off control unit performs on / off control of the connection switch transistor and the switch transistor at the time of reading at a timing of canceling switching noise. An image reading apparatus comprising the imaging device according to any one of claims 1 to 5. An image forming apparatus comprising the imaging device according to any one of claims 1 to 5. A charge accumulator that accumulates charges according to incident light; a charge detector that detects charges accumulated in the charge accumulator; a transfer transistor that transfers charges from the charge accumulator to the charge detector; and A plurality of pixel units each including at least a reset transistor that resets the charge detection unit; a pixel output unit that processes charges from the pixel units and sequentially transfers them to a subsequent circuit;
A charge storage capacitor provided in the pixel output unit for storing the charge detected by the charge detection unit, and a charge provided in the pixel output unit and detected by the charge detection unit in the charge storage capacitor. A plurality of write switch transistors for controlling the write timing, a plurality of read switch transistors provided in the pixel output unit for controlling the timing of reading the charge accumulated in the charge storage capacitor, and the pixel output And a plurality of connection switch transistors for controlling charge input / output of the charge storage capacitor at the timing of writing and reading,
A method for driving an imaging apparatus, comprising: a crosstalk prevention unit that prevents the crosstalk by the crosstalk prevention unit controlling the readout switch transistor independently of each pixel unit. In the crosstalk prevention step, the crosstalk prevention unit controls the readout switch transistor independently of each pixel unit, and controls the switch transistor that connects the charge storage capacitor to a predetermined potential. The method for driving an imaging apparatus according to claim 8, wherein crosstalk is prevented.

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