JP6432185B2 - Imaging apparatus, image reading apparatus, and image forming apparatus - Google Patents

Description

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

  In a batch exposure type imaging device in which Red, Green, and Blue pixels are arranged in the main scanning direction, the reset voltage and the photoelectric charges photoelectrically converted by the photodiode are batched for each pixel after exposure. It is known that the voltage level is written to each storage capacitor and then read as the voltage level in the order of the channels and output as an image level via a correlated double sampling (hereinafter referred to as CDS) circuit.

  Patent Document 1 discloses an amplification type solid-state imaging device that sequentially amplifies signals from light receiving elements included in a plurality of pixels, sequentially writes them in a capacitor, and sequentially reads out the signals written in the capacitor.

  However, in the column structure in which signals from a plurality of pixels are sequentially processed in one system, the time from batch writing to reading differs between channels, so that the amount of leakage current leaking from each storage capacitor differs. As a result, there is a problem that the influence of the leakage current on the read voltage level (that is, the image level) differs between channels for each color.

  Further, even when CDS is performed using the reset level and the signal level, if the read time difference between the reset level and the signal level is different between the channels, the influence of the leakage current is different between the channels.

  The present invention has been made in view of the above, and an imaging apparatus and an image that can reduce the occurrence of a level difference for each color due to a leakage current even when batch exposure is performed and each color is sequentially read out. An object is to provide a reading device and an image forming apparatus.

In order to solve the above-described problems and achieve the object, the present invention receives a plurality of light of different colors, and stores a plurality of charge storage units that respectively store charges according to the colors of the received light, A plurality of charge detectors for converting the charges stored in the charge storage units into voltages and outputting the voltages, and a plurality of first storages for storing reset signals output when the charge detectors are reset, respectively. A capacitor, a plurality of second storage capacitors that respectively store optical signals received by the plurality of charge storage units and converted into voltages by the plurality of charge detection units, the plurality of first storage capacitors, When reading the reset signal or the optical signal sequentially from the plurality of second storage capacitors for each color of light, the interval between the readout timing of the reset signal and the readout timing of the optical signal is set in advance. And having a control unit to align between light colors, the.

  According to the present invention, it is possible to reduce the occurrence of a level difference for each color due to a leakage current even when batch exposure is performed and reading is performed sequentially for each color.

FIG. 1 is a diagram illustrating an imaging apparatus according to an embodiment and the periphery thereof. FIG. 2 is a diagram illustrating a configuration of the pixel portion. FIG. 3 is a diagram illustrating a detailed configuration of the photoelectric conversion unit and a configuration of the signal processing unit. FIG. 4 is a timing chart illustrating a first operation example of the imaging apparatus. FIG. 5 is a timing chart illustrating a second operation example of the imaging apparatus. FIG. 6 is a timing chart illustrating a third operation example of the imaging apparatus. FIG. 7 is a timing chart illustrating a fourth operation example of the imaging apparatus. FIG. 8 is a timing chart illustrating a first operation example of the first modification of the imaging apparatus. FIG. 9 is a timing chart illustrating a second operation example of the first modification of the imaging apparatus. FIG. 10 is a diagram illustrating an overview of a second modification of the imaging device. FIG. 11 is a diagram illustrating a configuration example of the level correction unit. FIG. 12 is a diagram illustrating a configuration of a modification of the level correction unit. FIG. 13 is a timing chart illustrating a first operation example of the second modification of the imaging apparatus having the level correction unit. FIG. 14 is a timing chart illustrating a second operation example of the second modification of the imaging apparatus having the level correction unit. FIG. 15 is a diagram illustrating an outline of an image forming apparatus including an image reading apparatus having an imaging apparatus.

  An imaging apparatus according to an embodiment will be described below with reference to the accompanying drawings. FIG. 1 is a diagram illustrating an imaging apparatus 10 according to the embodiment and the periphery thereof. The imaging device 10 is a CMOS linear sensor having, for example, a photoelectric conversion unit 12, a signal processing unit 14, a control unit (timing control unit) 16, and a parallel-serial conversion unit (PS) 18, and operates according to the control of the CPU 11.

  The photoelectric conversion unit 12 includes N pixel units (including photodiodes) 120, 122, and 124 arranged in one direction for each of R, G, and B colors. In addition, the imaging apparatus 10 includes pixel units 120, 122, and 124 that receive light of three colors R, G, and B in one column (pixel group), and outputs a photoelectrically converted signal for each column. Is configured to do. Each pixel unit 120, 122, 124 photoelectrically converts the reflected light from the document and outputs it as an analog image signal for each pixel.

  The signal processing unit 14 includes N PGAs (Programmable Gain Amplifiers) 140, N A / D conversion units (ADC) 142, and N CDS units (D-CDS: digital CDS) 144. The photoelectric conversion unit 12 amplifies the analog signal output for each column, converts the analog signal into a digital signal, performs correction by correlated double sampling (CDS), and outputs the digital signal.

  Here, the PGA 140 is provided for each column, and amplifies the analog image signal in accordance with the dynamic range of the A / D conversion unit 142.

  The A / D conversion unit 142 converts the analog image signal output from the PGA 140 into a digital signal and outputs the digital signal to the CDS unit 144. The CDS unit 144 includes a reset level of the photoelectric conversion unit 12 indicated by the digital signal input from the A / D conversion unit 142 (a reference level output regardless of light) and each pixel (each pixel unit 120, 122, 124). CDS processing for calculating and outputting the difference from the signal level accumulated in (1). The parallel-serial conversion unit 18 serializes digital signals that are processed and output in parallel in a plurality of columns, and outputs them to the subsequent stage. Further, the control unit 16 generates and outputs each signal necessary for driving each unit constituting the imaging device 10. Further, the control unit 16 controls the operation timing so that the imaging apparatus 10 performs batch exposure.

  In the example shown in FIG. 1, a columnar CMOS linear sensor that processes a plurality of signals in parallel is taken as an example, but a single processing system may be used. In addition, a configuration of one column of three pixels in which one PGA 140, an A / D conversion unit 142, and a CDS unit 144 are provided for three pixels of R, G, and B is shown as an example. 6 pixels 1 column including R, G, and B of pixels and even pixels may be used. Further, although the imaging apparatus 10 has a configuration in which CDS is performed on A / D converted digital data as an example, a pixel using a reset level analog signal and a signal level analog signal amplified by the PGA 140 is used. Correlated double sampling may be performed every time.

  FIG. 2 is a diagram illustrating a configuration of the pixel unit 120 (pixel units 122 and 124). Hereinafter, # indicates either R (reset) or S (image signal), and * indicates any of R, G, and B. The transistor name and the signal name may be the same. The light receiving element PD, which is a charge storage unit, is a buried photodiode. The light receiving elements PD that respectively receive a plurality of different colors of light respectively generate charges corresponding to the light received within the accumulation time. The floating diffusion region FD that is the charge detection unit is a floating diffusion region, converts the charge to a voltage level, and outputs it to the subsequent stage.

  The reset transistor RT resets to the power supply voltage Vdd, which is the drain voltage of the reset transistor RT, or the source voltage (not shown) of the corresponding reset transistor RT before photocharge is transferred from the light receiving element PD. The transfer transistor TX transfers photocharges from the light receiving element PD to the floating diffusion region FD.

  FIG. 3 is a diagram illustrating a detailed configuration of the photoelectric conversion unit 12 and a configuration of the signal processing unit 14. In the photoelectric conversion unit 12, the R, G, and B pixel units 120, 122, and 124 are arranged in one direction (main scanning direction) as described above. In the nth column, the photoelectric conversion unit 12 includes a signal voltage VRn (*) at the time of reset from each of the pixel units 120, 122, and 124, and a signal voltage VSn (*) at the time of receiving light and performing photoelectric conversion. Are collectively written in each storage capacitor. The photoelectric conversion unit 12 then outputs the output PIXOUTn read in the order of R → G → B to one system (one PGA 140, A / D conversion unit 142, and R / G / B) for each of the three channels R, G, and B. Signal processing is performed by the CDS unit 144) (column configuration).

  Further, the photoelectric conversion unit 12 includes a storage capacitor CR (*) for resetting and a storage capacitor CS (*) for photoelectric conversion by receiving light in each of the pixel units 120, 122, and 124. Is provided. The capacity of CR (*) as the first storage capacity and the capacity of CS (*) as the second storage capacity are the same. The photoelectric conversion unit 12 is provided with a write switch transistor SL and switch transistors CR_ * and CS_ * for writing to and reading from each storage capacitor of each channel at a predetermined timing. Here, the transistor name and the signal name are the same. As described above, the control unit 16 outputs a signal for controlling each unit constituting the photoelectric conversion unit 12.

  The PGA 140 amplifies and outputs the PIXOUTn output from the pixel units 120, 122, and 124 in one system so as to match the dynamic range of the A / D conversion unit 142. The A / D conversion unit 142 performs analog-digital conversion on the analog image signal input from the PGA 140 and outputs the analog image signal to the CDS unit 144. The CDS unit 144 performs subtraction processing using the digital output of the reset signal and the digital output of the optical signal (image signal), and outputs a final image output CDSOUTn.

  FIG. 4 is a timing chart illustrating a first operation example of the imaging apparatus 10. The first operation example shown in FIG. 4 is an imaging apparatus from batch exposure (writing) per line to signal readout at the n-th column in the case of dark input (level at reset = light input level). There are 10 operations. Since the polarity of the charge is negative, the voltage value becomes lower as it becomes brighter.

  First, in the floating diffusion region FD, before the photoelectric charge is transferred from the light receiving element PD, the reset transistor RT causes the power supply voltage Vdd that is the drain voltage of the reset transistor RT or the source voltage (not shown) of the corresponding reset transistor RT. (T30).

  After that, the imaging device 10 converts the reset charge in the floating diffusion region FD into a reset signal, turns on the write switch transistor SL and the switch transistor CR_ * all at once, and all the pixels at the same time reset capacitor CR (* (T31).

  Next, the imaging device 10 turns off the switch transistors CR_ * all at once, turns on the transfer transistor TX, and transfers the photocharge from the light receiving element PD to the floating diffusion region FD after the reset charge transfer. The charge is converted into an optical signal (T32).

  Next, the imaging device 10 turns off the transfer transistor TX, turns on the switch transistors CS_ * at the same time for all channels, and transfers them to the optical signal storage capacitor CS (*) (T33).

  Then, the imaging apparatus 10 turns off the switch transistors CS_ * at the same time for all channels, and finishes the batch writing of the reset signal and optical signal storage capacitors.

  Next, the imaging device 10 turns on the selection transistor SW and simultaneously turns on the switch transistor CR_R first, thereby resetting the reset signal voltage VRn (R) stored in the reset signal storage capacitor CR (R) of the R pixel. ) Is transferred to PIXOUTn (T34). The black dot of VRn (R) shown in FIG. 4 represents the level at the end of reading. This level is amplified by the PGA 140 at the subsequent stage and AD-converted by the A / D converter 142 (the same applies to the black points of other channels).

  After transferring the reset signal voltage VRn (R), the imaging device 10 stores the light signal storage capacitor CS (R) of the R pixel by turning off the switch transistor CR_R and similarly turning on the switch transistor CS_R. The optical signal voltage VSn (R) being transferred is transferred to PIXOUTn (T35). Then, after transferring the optical signal voltage VSn (R), the imaging device 10 turns off the switch transistor CS_R.

  The imaging apparatus 10 applies the same signals stored in the respective storage capacitors (CR (G), CS (G), CR (B), CS (B)) to the G pixel and the B pixel as well. (T36).

  In this manner, PIXOUTn from T30 to T36 changes in potential in the order of the channels by reading signals (R reset signal voltage VRn (R) → R optical signal voltage VSn (R) → G reset signal voltage. VRn (G) → G optical signal voltage VSn (G) → B reset signal voltage VRn (B) → B optical signal voltage VSn (B)).

  Incidentally, it is known that a storage capacitor for reading a signal generally generates a leakage current during a period in which the voltage after storage is held. Since a slight current flows between the insulated electrodes in the capacitor and is generally very small, the discharge characteristic is considered to be a linear approximation. Therefore, when the voltage of the capacitor is read in channel order after the batch write operation is completed, CR (R), CS (R), CR (G), CS (G), CR (B), and CS (B) are read. Due to the time difference between the two, a difference occurs in the amount of leakage current, and a deviation occurs in the voltage value.

  Since the imaging apparatus 10 performs the difference calculation between the reset signal and the optical signal by the CDS unit 144, the influence difference due to the leakage current between the reset signal and the optical signal affects the final output value CDSOUTn after CDS. Also, if the difference in influence due to the leakage current between the reset signal and the optical signal is different between channels, the output value after the final CDS will be different between RGB when a uniform color (black or white) is input as the color. End up.

  For example, in the first operation example, the reset signal read timing and the optical signal read timing differ between the three RGB channels (Tr_r−Ts_r ≠ Tr_g−Ts_g ≠ Tr_b−Ts_b). The difference, that is, the output value CDSOUTn after CDS differs between channels (VSn (R) −VRn (R) ≠ VSn (G) −VRn (G) ≠ VSn (B) −VRn (B)).

  FIG. 5 is a timing chart illustrating a second operation example of the imaging apparatus 10 (during dark input when each capacitor capacity is large). In the second operation example, the imaging apparatus 10 aligns the interval between the reset signal readout timing Tr_ * and the optical signal readout timing Ts_ * after batch writing of the RGB channels (Tr_r−Ts_r = Tr_g−Ts_g = Tr_b−Ts_b). As shown in FIG.

  When the capacitance of each capacitor of the imaging device 10 is large, the level attenuation due to the leakage current in the storage capacitor voltages VRn (*) and VSn (*) can generally be considered by approximating a straight line. When the level attenuation is linearly approximated, the level attenuation is proportional to the time difference. Therefore, if the readout time difference of each pixel portion is the same, the difference between the optical signal and the reset signal, that is, the influence of the leakage current on the output value CDSOUTn after CDS can be made uniform among the channels. That is, when performing the operation shown as the second operation example, the imaging apparatus 10 can prevent a decrease in offset difference and color reproducibility when uniform input (black or white) is given as a color. (VSn (R) -VRn (R) = VSn (G) -VRn (G) = VSn (B) -VRn (B)).

  FIG. 6 is a timing chart illustrating a third operation example (when each capacitor capacity is small) of the imaging device 10. As shown in FIG. 3, the storage capacitor is provided in each pixel, and the area ratio in the imaging device 10 is large. Further, the discharge characteristic of the leakage current of the capacitor can generally be considered as approximating a straight line. However, a capacitor is an insulation resistance connected in parallel to a capacitor with a simple equivalent circuit, and the voltage attenuates in a non-linear manner theoretically with the product of the insulation resistance value and the capacitance value as the self-discharge time constant τ. . When the capacitance values CR (*) and CS (*) are reduced, the discharge time constants τr (*) and τs (*) are reduced, the amount of leakage current is increased, and the capacitor is discharged with respect to the discharge time. The characteristic cannot be approximated to a straight line.

  In this case, the attenuation of the capacitor voltages VRn (*) and VSn (*) due to the leakage current is considered to change in a non-linear manner (exponential function) instead of the straight line as shown in FIG. That is, even if the interval between the read timing Tr_ * of the reset signal and the read timing Ts_ * of the optical signal is uniform between RGB, the absolute time from the completion of batch writing to the read time is different (Tr_r ≠ Tr_g ≠ Tr_b, Ts_r ≠ Ts_g ≠ Ts_b), and the difference between the reset signal voltage and the optical signal voltage differs between RGB (VSn (R) −VRn (R) ≠ VSn (G) −VRn (G) ≠ VSn (B) − VRn (B)). That is, the influence of leakage on the output value after CDS differs between channels.

  Since the attenuation curve can be considered as an exponential function, in FIG. 6, after completion of batch writing (after the start of discharge), Red, which is the first readout channel, is the difference between the optical signal and the reset signal (VSn (R) −VRn (R)). And then the difference decreases in the order of Green (VSn (G) −VRn (G)) and Blue (VSn (B) −VRn (B)).

  FIG. 7 is a timing chart illustrating a fourth operation example of the imaging device 10 (optical signal: when reading in the dark). Although the discharge time constants τr (*) and τs (*) are the same, in order to make the influence of the leakage current between the reset signal and the optical signal uniform between RGB, the control unit 16 determines the interval between the readout timing of the reset signal and the optical signal. Is different for each channel.

  Specifically, the control unit 16 has the largest amount of change in Red, which is the first read channel, and the rate of change decreases as it becomes behind Green and Blue. The controller 16 sets the interval between the readout time of the reset signal and the optical signal as Tr_r−Ts_r <Tr_g−Ts_g <Tr_b−Ts_b, and finally sets VSn (*) according to the discharge time constants τr (*) and τs (*). The readout time of each channel is set so that R) −VRn (R) = VSn (G) −VRn (G) = VSn (B) −VRn (B).

  In this case, even if the time from the completion of batch writing to the reading time is different (Tr_r ≠ Tr_g ≠ Tr_b, Ts_r ≠ Ts_g ≠ Ts_b), the control unit 16 does not cause a difference in the optical signal-reset signal between RGB. Read timings for each of RGB are set. Therefore, the imaging device 10 can align the optical signal-reset signal, that is, the output value CDSOUTn after CDS, between channels, and can suppress an offset difference that becomes particularly noticeable in a dark image.

  The imaging apparatus 10 performs the CDS operation after the A / D conversion unit 142 converts the digital data into digital data. However, this is an example, and the CDS operation is performed by taking a difference with an analog signal. Also good.

  Next, a first modification of the imaging device 10 will be described. The first modification of the imaging device 10 is configured so that the capacitance value of the storage capacitor differs between RGB. Hereinafter, a first modification of the imaging device 10 will be described with reference to FIGS. FIG. 8 is a timing chart showing a first operation example (optical signal: during dark reading) of the first modification of the imaging apparatus 10.

  The first modification of the imaging device 10 is self-aligned so that there is no difference in the amount of leakage current between the reset signal and the optical signal at the readout timing of each channel in order to align the influence of the leakage current of the reset signal and the optical signal between RGB. The discharge time constants τr (*) and τs (*) are different for each channel. Specifically, in the first modification of the imaging device 10, CR (*) and CS (*) shown in FIG. 3 are changed from CR (R) (CS (R))> CR (G) (CS (G ))> CR (B) (CS (B)) so that the capacitance values of the storage capacitors differ between RGB.

  In this case, even if the time from the completion of batch writing to the reading time is different (Tr_r ≠ Tr_g ≠ Tr_b, Ts_r ≠ Ts_g ≠ Ts_b), reset accumulation is performed for each RGB so that there is no difference in light signal-reset signal between RGB. Since the capacitance values CR (*) and CS (*) of the capacitor for optical signal and the capacitor for storing optical signal are set, the optical signal-reset signal, that is, the output value CDSOUTn after CDS is aligned between channels (VSn (R) −VRn (R) = VSn (G) −VRn (G) = VSn (B) −VRn (B)), an offset difference that is particularly noticeable in a dark image is suppressed.

  In the first modification of the imaging apparatus 10 as well, the CDS operation is performed after the A / D conversion unit 142 converts the digital data into digital data. However, this is an example, and the CDS operation is performed by taking a difference with an analog signal. It may be configured as follows.

  FIG. 9 is a timing chart showing a second operation example (optical signal: bright (white) reading) of the first modification of the imaging apparatus 10. The first modification of the imaging device 10 can absorb the offset difference in the case of dark input, but the effect of the leak current in the light input even in the same readout time compared to the dark input (reset level). Is small. This is because if the voltage at the end of collective writing (discharge start) is low, the difference from the start of discharge becomes smaller than that at dark time.

  In the first modification of the imaging apparatus 10, if the RGB optical signal-reset signal is subtracted in this state, the output value CDSOUTn after CDS differs between channels (VSn (R) -VRn (R ) ≠ VSn (G) −VRn (G) ≠ VSn (B) −VRn (B)). As described above, the first modification of the imaging device 10 is not as prominent as the dark image, but completely suppresses the level difference between RGB due to the leakage current discharged as an exponential function and the light input. I can't.

  Next, a second modification of the imaging device 10 will be described. FIG. 10 is a diagram illustrating an outline of a second modification of the imaging device 10. 10 shows a detailed configuration of the photoelectric conversion unit 12 and a modified example of the signal processing unit 14, and substantially the same components as those shown in FIG. 3 are denoted by the same reference numerals. is there. For example, the level correction unit 20 corrects a level variation due to a leak current for a digital signal output from the A / D conversion unit 142.

  FIG. 11 is a diagram illustrating a configuration example of the level correction unit 20. In the level correction unit 20, the calculation units 201 to 206 hold the capacitance values CR (*) and CS (*) of the storage capacitor and the insulation resistance value R (*) as design values in advance.

  Hereinafter, the correction performed by the level correction unit 20 will be described using a reset signal as an example. At the end of batch writing (discharge start, T31 end for reset signal, T33 end for optical signal), t = 0, the image level after analog-digital conversion of the reset signal at that time is Dr0n (*), reset signal If t = tr and the image level at that time is Drn (*), the relationship between them is as shown in Equation 1 below.

  Since the above equation 1 is solved for Dr0n (*) because of the value before the occurrence of leak that is to be obtained here, that is, Dr0n (*), the following equation 2 is obtained.

  Since the level correction unit 20 knows the values of Drn (*), t, CR (*), and R (*), the above equation 2 is simultaneously applied to all pixels in the main scanning direction, and Dr0n (*) is set. By obtaining this value, the value is replaced with a value that is not affected by the leak, and is output to the subsequent CDS unit 144.

  The level correction unit 20 also applies this to the optical signal, and uses Dsn (*) when t = ts according to the following expressions 3 and 4, and replaces it with Ds0n (*). The level correction unit 20 performs this operation in the order of RGB, like the A / D conversion unit 142 and the CDS unit 144.

  The level correction unit 20 includes calculation units 201 to 206 for a total of 6 channels of RGB reset signals and optical signals, and by turning on / off the switch transistors CR_ * and CS_ * for each corresponding channel. The signals of the respective channels are input to the arithmetic units 201 to 206, but the arithmetic units may be made common if the storage capacitor capacitance values C # (*) (#: R, S) are the same value.

  As described above, in the second modification of the imaging device 10, if the input is not the saturation level, the level can be corrected to the value immediately after the end of the batch writing regardless of the exposure level. That is, the second modification of the imaging device 10 can cope with a level change due to a leakage current at the white side (light time) input, and can suppress differences between channels and a level change due to the leakage current. .

  FIG. 12 is a diagram illustrating a configuration of a modified example (level correction unit 20 a) of the level correction unit 20. The level correction unit 20a stores, in the arithmetic units 201 to 206, information (equivalent to τ # (*)) of the capacitance value C # (*) and the insulation resistance value R (*) of the storage capacitor. 216 respectively. The level correction unit 20a can change information (corresponding to τ # (*)).

  FIG. 13 is a timing chart showing a first operation example (in-line operation in the level correction expression acquisition mode) of the second modified example of the imaging apparatus 10 having the level correction unit 20a. In the second modification of the imaging device 10 having the level correction unit 20a, the level correction type acquisition mode is switched ON / OFF according to register control (not shown) or a control signal from the outside. In FIG. 13, for simplification of explanation, only one of the channels is shown.

  As described above, the second modification of the imaging device 10 having the level correction unit 20 includes the capacitance value C # (*) of the storage capacitor and the insulation resistance value R (*) as the discharge time constant τ # (*). Information is previously stored in the calculation units 201 to 206. In general, the capacitance value C # (*) and the insulation resistance value R (*) vary depending on the surrounding environment, changes with time, manufacturing variations of the second modification of the imaging device 10, and the like. As described above, when the capacitance value C # (*) and the insulation resistance value R (*) vary, the values held by the calculation units 201 to 206 are different from the actual values, and Dr0n ( *) When obtaining Ds0n (*), the accuracy is lowered.

  The second modification of the imaging device 10 having the level correction unit 20a (hereinafter referred to as the imaging device 10a) samples a plurality of points (two points in FIG. 13) of the elapsed time from the batch writing and the image data at that time. From this tendency, an equation for attenuation of the capacitor voltage V # n (*) due to the leakage current is generated, the discharge time constant τ # (*) at that time is obtained, and the level correction equation is calculated.

  As illustrated in FIG. 13, the imaging device 10a operates in the following order. First, when the level correction type acquisition mode is turned on, the reset transistor RT is turned on, and the reset signal voltage is input to the storage capacitor (T120).

  Next, the switch transistor C # _ * is turned OFF, and writing is completed (T121). In the example shown in FIG. 13, the transfer transistor TX is not particularly turned on. However, in the dark state (equivalent to the reset voltage), the transfer transistor TX is turned on and the reset transistor RT is not turned on. Also good.

  Next, by turning on the selection transistor SW and simultaneously turning on the switch transistor C # _ *, the signal stored in the storage capacitor C # n (*) is transferred to PIXOUTn.

  After this transfer, the switch transistor C # _ * is turned OFF, and the image data D # 1n at that time (t = T1) is acquired and stored in the memories 211 to 216 shown in FIG. 12 (T122).

  Similarly, at the timing after T1 (T123), the switch transistor C # _ * is turned on again, and the voltage of the storage capacitor C # n (*) is transferred to PIXOUTn. At that time (t = T2), the image data D # 2n is acquired and stored in the memories 211 to 216 shown in FIG. 12 (T124).

  The data of D # 1n and D # 2n to be acquired may be an average value of a specific column in one line or a value of a specific one pixel. The imaging device 10a derives an equation for a voltage attenuation curve due to leakage using the acquired values of T1, T2, D # 1n, and D # 2n.

  First, simultaneous equations (5) and (6) below are set to 1 when t = 0, and the discharge time constant τ # (*) is solved.

  That is, the following expression 7 is an expression for obtaining the final discharge time constant τ # (*), and the calculation result is stored in the memories 211 to 216 shown in FIG.

  Note that the imaging device 10a sequentially obtains the discharge time constant τ # (*) in the same manner in the other channels and stores it in the memories 211 to 216, and ends the level correction expression acquisition mode. Therefore, the imaging apparatus 10a needs time to acquire at least the number of lines corresponding to the number of channels in the level correction type acquisition mode. Thereafter, at the time of image data output, the imaging device 10a performs level correction by the above-described level correction formula using the discharge time constant τ # (*) stored in the memories 211 to 216. In this way, the imaging apparatus 10a updates the discharge time constant τ # (*), which has fluctuated due to the surrounding environment, changes with time, manufacturing variations, and the like, in the level correction expression acquisition mode, thereby calculating the formulas 2 and 4 above. Can be reflected.

  FIG. 14 is a timing chart showing a second operation example (multiple line operation in the level correction expression acquisition mode) of the second modification of the imaging apparatus 10 having the level correction unit 20a. In the first operation example of the imaging apparatus 10a described above, when the output level is acquired at a plurality of predetermined timings, the discharge time constant is calculated using the acquired data only within one line. However, only within one line. However, the accuracy may not be improved if there is an influence of noise such as sudden disturbance. In addition, the average value of a specific column in one line also changes the acquired value if there is a level distribution due to the wiring pattern or the like in the power supply voltage Vdd.

  Therefore, in the second operation example of the imaging device 10a, in a pixel that is not affected by the fluctuation of the power supply voltage Vdd, the same operation is performed on a plurality of lines, and the average value obtained is obtained to thereby reduce the influence of noise. The leak current equation is derived with a suppressed acquisition level, and the robustness of the leak correction accuracy is improved.

  Specifically, as illustrated in FIG. 14, the imaging device 10a acquires the image data D1_m and D2_m at the same timing T1 and T2 for each line in a plurality of lines instead of one line for each channel (FIG. 14). Then, m = M lines) The imaging device 10a uses these average values as acquisition levels and substitutes them into the following equations 8 and 9, and finally obtains the discharge time constant based on the following equation 10.

  Thereby, the imaging device 10a can calculate the discharge time constant τ # (*) based on the acquisition level in which the influence of noise and the fluctuation influence of the power supply voltage in one line are suppressed. However, in this case, the average number of lines increases, and the operation time of the level correction type acquisition mode increases. Therefore, the average number of lines is determined from the relationship between the noise effect and the processing time.

  Next, an image reading apparatus and an image forming apparatus provided with the imaging apparatus 10 according to the embodiment will be described. FIG. 15 is a diagram illustrating an outline of an image forming apparatus 50 including an image reading device 60 having the imaging device 10. 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, the imaging device 10, an LED driver (LED_DRV) 600, and an LED 602. The LED driver 600 drives the LED 602 in synchronization with, for example, a line synchronization signal output from the control unit 16. The LED 602 irradiates the original with light. The imaging apparatus 10 receives reflected light from a document in synchronization with a line synchronization signal or the like, and a plurality of light receiving elements (PD) (not shown) generate electric charges and start accumulation. The imaging apparatus 10 outputs image data to the image forming unit 70 after performing parallel serial conversion or 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 11. The CPU 11 executes a program stored in a memory (not shown) or the like, and controls each part of the image forming apparatus 50 such as the imaging apparatus 10. In addition, the CPU 11 or the control unit 16 performs control so that each PD starts generating charges according to the amount of received light substantially simultaneously.

  The imaging device 10 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.

  Note that the image reading device 60 can improve the offset difference and color reproducibility of the scanner image because the imaging device 10 suppresses image level fluctuations due to leakage current. In addition, by turning on the level correction type acquisition mode at least one of when the image reading apparatus 60 is turned on and at a standby time other than the reading operation, the correction accuracy of the image level fluctuation due to the leakage current can be optimized. . Further, the image reading device 60 can suppress the influence due to the change in the surrounding environment after the power is turned on by turning on the level correction type acquisition mode before starting the scan mode.

  Further, the image forming apparatus 50 can improve the offset difference and color reproducibility of the copy image because the image capturing apparatus 10 suppresses the image level fluctuation due to the leakage current. Further, by turning on the level correction type acquisition mode at least one of when the image forming apparatus 50 is turned on and at the time of standby other than the reading operation, the correction accuracy of the image level fluctuation due to the leakage current can be optimized. . Further, the image forming apparatus 50 can suppress the influence due to the change of the surrounding environment after the power is turned on by turning on the level correction type acquisition mode before starting the copy mode.

  Each embodiment has been described above, but the specific configuration, processing contents, data format, and the like of each unit are not limited to those described in the embodiment. Moreover, it is needless to say that the configurations of the embodiments described above can be implemented in any combination as long as they do not contradict each other.

PD Charge storage unit (light receiving element)
FD Charge detector (floating diffusion region)
CR (*) First storage capacitor CS (*) Second storage capacitor 10 Imaging device 11 CPU
DESCRIPTION OF SYMBOLS 12 Photoelectric conversion part 14 Signal processing part 16 Control part 18 Parallel serial conversion part 20, 20a Level correction part 50 Image forming apparatus 60 Image reading apparatus 70 Image forming part 120,122,124 Pixel part 140 PGA
142 A / D conversion unit 144 CDS unit 201-206 Calculation unit 211-216 Memory

Japanese Patent No. 4846076

Claims (8)

A plurality of charge storage units that receive a plurality of different colors of light and store charges according to the colors of the received light; and
A plurality of charge detection units that convert the charges accumulated in the plurality of charge accumulation units into voltages and output the respective voltages;
A plurality of first storage capacitors for respectively storing reset signals output when the plurality of charge detection units are reset;
A plurality of second storage capacitors for storing optical signals received by the plurality of charge storage units and converted into voltages by the plurality of charge detection units, respectively;
When the reset signal or the optical signal is read out sequentially for each color of the light from the plurality of first storage capacitors and the plurality of second storage capacitors, the reset signal read timing, and the optical signal A control unit that aligns the interval between the reading timing of the light between the colors of the light,
An imaging device comprising: The controller is
Based on the leakage current amounts of the plurality of first storage capacitors and the plurality of second storage capacitors, the interval between the reset signal read timing and the optical signal read timing is controlled for each color of the light. The imaging apparatus according to claim 1, wherein: The reset read from the plurality of first storage capacitors and the plurality of second storage capacitors based on the capacitance value and the insulation resistance value of each of the plurality of first storage capacitors and the plurality of second storage capacitors. the imaging apparatus according to claim 1 or 2, characterized by further comprising a level correcting unit for correcting the level of the signal and the optical signal. The level correction unit
Leakage from the level of the reset signal or the optical signal read from the plurality of first storage capacitors and the plurality of second storage capacitors at a plurality of predetermined timings in one read of the reset signal or the optical signal The imaging apparatus according to claim 3 , wherein a current discharge time constant is calculated, and the levels of the reset signal and the optical signal are corrected based on the calculated discharge time constant. The level correction unit
In the reading of the reset signal or the optical signal a plurality of times, the discharge time constant is calculated a plurality of times, and the levels of the reset signal and the optical signal are corrected based on the calculated plurality of discharge time constants. The imaging device according to claim 4 . Image reading apparatus characterized by having an imaging device according to any one of claims 1 to 5. It has an imaging device given in any 1 paragraph of Claims 3 thru / or 5 ,
The level correction unit
An image reading apparatus that corrects the level of the reset signal and the optical signal at least when the power is turned on and at the time of standby other than the reading operation. An image reading apparatus according to claim 6 or 7,
An image forming apparatus comprising: an image forming unit that forms an image based on image data read by the image reading apparatus.

Images