JP7052337B2 - Image reader, image reading method, and image forming device - Google Patents

Description

The present disclosure relates to an image reading device, an image reading method, and an image forming device.

In recent years, the number of reading special documents such as three-dimensional objects and precious metals has increased by an image reading device provided in an image forming device such as an MFP (Multifunction Peripheral) having a copy function and a scanner function. In this case, the PD (Photodiode) in the image reader receives the scattered light reflected by the special change through the mirror or the lens. The PD generates an electric charge according to the amount of incident light, and outputs an analog signal according to the amount of electric charge to an AFE (Analog Front End) that performs various signal processing in the subsequent stage via a capacitor. AFE converts an analog signal into a digital signal (data) by A / D conversion (Analog / Digital Conversion). As a result, the image reading device reads the image of the original (reading target).

Here, the configuration of a conventional image reader will be described with reference to FIGS. 11 and 12. FIG. 11 is a configuration diagram of a conventional image reader. As shown in FIG. 11, the conventional image reader includes a signal generator 1000, a capacitor 8000 and an AFE9000. The signal generation unit 1000 includes a photoelectric conversion unit 1010 such as a PD, a charge / voltage conversion unit 1020, and an output unit 1030.

When the document is irradiated with light from a light source when the document is read by the image reader, the scattered light reflected by the document is incident on the photoelectric conversion unit 1010 as an optical signal through a mirror or a lens. The photoelectric conversion unit 1010 generates a charge corresponding to the amount of incident light, and the charge-voltage conversion unit 1020 converts the charge into a voltage corresponding to the amount of charge. Then, an analog signal of the voltage V _CCDout (hereinafter referred to as “voltage signal V _CCDout ”) is output from the output unit 1030. As a result, an analog signal of voltage V _AFEin (hereinafter referred to as “voltage signal V _AFEin ”) is input to AFE9000 via the capacitor 8000.

FIG. 12 (a) shows the voltage value (V CCDout) of the voltage signal from the signal generator with respect to the elapsed time (t), and FIG. 12 (b) shows the voltage value (V _CCDout ) of the voltage signal to AFE with respect to the elapsed time (t). V _AFEin ) is shown. As shown in FIG. 12A, the voltage signal V _CCD out of the signal generation unit 1000 is a signal having a DC voltage V _off as an offset component and an amplitude V _sig as an image signal component. Further, the voltage signal V _CCDout is output to the AFE9000, but since the operating voltage is different between the signal generation unit 1000 and the AFE9000, the voltage signal V _CCDout of the signal generation unit 1000 is AC-coupled by the capacitor 8000, and this AC coupling is performed. Only the change in the signal is output to the AFE9000 in the subsequent stage. Then, in the input unit of the AFE9000, the offset voltage V _CLP generated inside the _AFE9000 is applied to the change of the voltage signal V CCD out, and the voltage V _AFE in shown in FIG. 12B is generated. The AFE9000 performs various analog signal processing on the voltage signal of this voltage V _AFEin and A / D-converts it into a digital signal (data) to realize reading of an image of a document.

However, when the image reader reads a special document, the specular reflected light having an excessive amount of light with respect to the scattered light at the time of reading a general document may be incident on the photoelectric conversion unit 1010 due to the difference in the reflection angle. There are some defects in the image data due to this effect. For example, when an excessive image signal is output from the signal generation unit 1000 to the AFE9000 via the capacitor 8000 when the specular reflected light is incident, the protection built in the input unit of the AFE9000 for the purpose of preventing the failure of the AFE9000. The diode works. In this case, when the negative electrode excessive signal is input to the AFE9000, the AFE9000 level shifts the excessive signal to the high voltage side in order to keep the excessive signal within a certain range. Due to this effect, there is a problem that a black horizontal streak-like abnormal image is generated on the output image. This problem will be specifically described with reference to FIGS. 13 and 14. FIG. 13 (a) is a diagram showing a voltage signal of a charge-voltage conversion unit in a conventional image reader, and FIG. 13 (b) is a diagram showing a voltage signal of AFE in a conventional image reader. FIG. 14 (a) is a diagram showing an AFE voltage signal when normal light is received after excessive light as reflected light by a conventional image reader, and FIG. 14 (b) is a diagram showing a reading target by a conventional image reader. It is a figure which showed the output image at the time of reading.

When the image reader reads a special document such as a precious metal, the reflection angle is different from that when the image reader reads a flat general document. Therefore, specularly reflected light having an excessive amount of light with respect to the scattered light in the special document may be incident on the photoelectric conversion unit 1010. In this case, as shown in FIG. 13A, the signal generation unit 1000 outputs an analog voltage signal V _CCD out having an excessive amplitude V _ovr as compared with the case where the scattered light is read. After that, as shown in FIG. 13 (b), the signal output V _CCD out is AC-coupled by the capacitor 8000 in the subsequent stage, and the offset voltage V _CLP generated inside the AFE 9000 to the change of the V _CCD out at the input portion of the AFE 9000. Is applied to the voltage signal V _AFEin , which is input to the AFE9000.

Here, the minimum voltage of the voltage signal V _AFEin of AFE9000 is V _CLP -V _ovr , but as shown in FIG. 13B, when this minimum voltage is lower than 0V, the input section of AFE9000 and GND Between them, a current flows through the protection diode connected for the purpose of failure prevention. In this case, as shown in FIG. 13 (c), the voltage of the input portion of the AFE9000 connected to GND via the diode is set to the high voltage side so that the average voltage during the clamping period becomes 0V. The level shifts.

Immediately after this level shift, when the voltage signal V AFE in at the time of normal light incident is input to the input unit of the _AFE9000 , the signal width of the voltage signal V _AFE in becomes equal to or less than the level shift width V _sif due to the excessive light incident. Then, this image signal level is determined to be 0 (black) as digital data after A / D conversion. Each line is clamped to the original offset voltage V _CLP , but due to the short clamping period, it cannot return to the original voltage level with a single clamping operation. Therefore, as shown in FIG. 14A, even if the reflected light incident on the PD returns from the excessive light to the normal light, the voltage level of the voltage signal to the AFE9000 gradually decreases for each line. turn into. Due to this operation, immediately after the incident of the excessive light, it appears as a black horizontal streak-like abnormal image (part A in FIG. 14 (b)). After that, while V _sif is fully returned, it becomes a gray horizontal streak-like abnormal image (B part of 14 (b)), and then V _sif returns to a normal image (C in FIG. 14 (b)). part). As described above, in FIG. 14A, the intensity of the voltage signal to the AFE9000 due to the excessive light is as shown in FIG. 13C, and the intensity of the voltage signal to the AFE9000 due to the normal light is the A portion, the B portion, and so on. By gradually lowering in the order of the image of the C part, the images of the A part, the B part, and the C part of FIG. 14A appear. Although a negative electrode signal is taken as an example here, the same phenomenon occurs in a positive signal such as a CIS (Contact Image Sensor). At this time, a white horizontal streak-like abnormal image is generated instead of black.

In order to prevent the occurrence of such an abnormal image, a technique is already known in which a voltage dividing circuit 7000 is built in between the photoelectric conversion unit 1000 and the capacitor 8000 to limit the input of an excessive signal to the AFE9000 (). See Patent Document 1). Here, the technique described in Patent Document 1 will be described with reference to FIGS. 15 and 16. FIG. 15 is a diagram showing an electrical configuration of the image reader described in Patent Document 1. FIG. 16 shows a voltage signal based on excessive light as in FIGS. 13 (b) and 13 (c), and FIG. 16 (a) shows a voltage signal of AFE when the technique described in Patent Document 1 is used. It is a figure which showed. Note that FIG. 16B is a diagram showing a voltage signal of AFE when the invention according to the first embodiment described later is used.

As shown in FIG. 15, Patent Document 1 describes that a voltage dividing circuit 7000 is provided between the signal generation unit 1000 and the capacitor 8000, and the voltage is divided at a predetermined voltage dividing ratio. The dividing circuit 7000 generates an analog signal A2 by dividing the voltage signal V _CCDout (analog signal A1) of the signal generation unit 1000 at a predetermined voltage dividing ratio. The capacitor 8000 generates a voltage signal V AFEin (analog signal A3) by cutting the DC voltage component contained in the analog signal A2 output from the voltage dividing circuit 7000, and outputs the voltage signal V _AFEin (analog signal A3) to the AFE9000.

Here, the voltage dividing circuit 7000 will be described more specifically. As shown in FIG. 15, the voltage divider circuit 7000 has an input terminal (input unit) T1 to which an analog signal A1 output from a signal generation unit 1000 is input, and a resistor having one end connected to the input terminal T1. It includes a resistor (first resistor) R1 and a resistor (second resistor) R2 having one end connected to the other end of the resistor R1 and the other end connected to GND. The voltage divider circuit 7000 divided the analog signal A1 output from the signal generation unit 1000 at a predetermined voltage dividing ratio DR determined by the resistance value r1 of the resistor R1 and the resistance value r2 of the resistor R2, and divided the voltage. The analog signal A2 is output to the capacitor 8000.

This voltage division ratio is the maximum value of the amplitude of the analog signal that can be input to the AFE9000 with respect to the maximum value of the amplitude of the analog signal A1 output from the signal generation unit 1000 when the light emitted from the light source is positively reflected by the document. It is less than the ratio of. Therefore, the maximum value of the amplitude of the analog signal A3 after being AC-coupled by the capacitor 8000 is limited to the maximum value of the amplitude of the analog signal that can be input to the AFE9000, which is shown in FIG. 14 (b). It is possible to suppress the occurrence of such an abnormal image.

However, in the method described in Patent Document 1, the voltage dividing applied to the voltage signal V _CCD out of the signal generation unit 1000 is also applied to ordinary incident light such that excessive light is not incident. Therefore, the amplitude of the image signal becomes small by dividing the voltage signal V _CCD out. In this case, since the ratio of noise components such as disturbances received after the voltage dividing point is larger than that of the voltage signal V _CCD out, the influence of noise is higher than that in the case where the voltage is not divided. That is, even when the image reading device 10 reads a general document, the voltage signal V _CCDout from the signal generation unit 1000 becomes smaller by dividing the voltage, so that the S / N ratio of the output image when the document is read decreases. Therefore, as shown in FIG. 16A, the degree of influence by noise becomes larger than that in the case where the voltage is not divided. As a result, the technique described in Patent Document 1 has a problem that the roughness of the output image becomes conspicuous.

In order to solve the above-mentioned problems, the invention according to claim 1 has a signal generation unit that receives reflected light to be read and generates a voltage signal according to the amount of the reflected light, and the voltage signal . An image reading device that reads an image to be read by comprising a signal processing unit that performs signal processing for outputting to an image forming unit that forms an image, and the signal generation unit has an amplitude of the voltage signal. The limiting means is provided with limiting means for limiting the level so as not to exceed a predetermined level, and the limiting means limits the amplitude of the voltage signal to a predetermined level based on the voltage generating unit for generating the reference voltage in the limiting means and the reference voltage. It is characterized in that it has a signal limiting unit, and the signal limiting unit is composed of a single MOSFET .

According to the present invention, the signal generation unit has a limiting means for limiting the amplitude of the voltage signal so as not to exceed a predetermined level, thereby preventing the occurrence of black streaks and the like in the image and suppressing the roughness of the image. It has the effect of being able to do it.

It is a figure which shows the whole structure in the image forming apparatus which concerns on 1st Embodiment. It is a figure which shows the whole structure in the image reading part which concerns on 1st Embodiment. It is a figure which showed the electric structure of the image reader which concerns on 1st Embodiment. (A) is a diagram showing the output voltage of the charge-voltage conversion unit, (b) is a diagram in which the voltage of the voltage signal of the charge-voltage conversion unit is limited by the limiting unit, and (c) is a diagram showing the voltage signal of the AFE. (D) is a diagram showing the voltage signal of AFE when excessive light and normal light are incident on the photoelectric conversion unit. It is a figure which showed the case where the voltage signal of a signal generation part was affected by the variation of the circuit of an output part when the invention of 1st Embodiment was used, and (a) is the minimum voltage by variation of a circuit. (B) shows the maximum voltage due to the variation of the circuit. FIG. 3 is an electrical configuration diagram showing a modified example of the signal generation unit according to the second embodiment. It is a figure which showed the voltage signal of the charge-voltage conversion part when the invention of 2nd Embodiment was used. FIG. 3 is an electrical configuration diagram showing a modified example of the signal generation unit according to the third embodiment. According to the third embodiment, according to the third embodiment, (a) is a diagram showing a voltage signal of a signal generation unit and an AFE voltage signal when there is no charge limitation, and (b) has a charge limitation. It is a figure which showed the voltage signal of the signal generation part of the case, and the voltage signal of AFE. FIG. 5 is an electrical configuration diagram showing a modified example of the signal generation unit according to the fourth embodiment. It is a figure which showed the electric structure of the conventional image reader. It is a figure which showed the output voltage of the charge voltage conversion part in the conventional image reading apparatus, (b) is the figure which showed the input voltage of AFE in the conventional image reading apparatus. (A) is a diagram showing a voltage signal of a charge-voltage conversion unit in a conventional image reader, and FIG. 13 (b) is a diagram showing a voltage signal of AFE in a conventional image reader. (A) is a diagram showing an AFE voltage signal when normal light is received after excessive light as reflected light by a conventional image reader, and FIG. 14 (b) is a diagram in which a reading target is read by a conventional image reader. It is a figure which showed the output image of the case. It is a figure which showed the electric structure of the image reading apparatus described in Patent Document 1. FIG. A voltage signal based on excessive light is shown, (a) is a diagram showing an AFE voltage signal when the technique described in Patent Document 1 is used, and (b) is a diagram showing the voltage signal according to the first embodiment. It is a figure which showed the voltage signal of AFE in the case of.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
First, the first embodiment will be described with reference to FIGS. 1 to 4.

<Overall configuration>
FIG. 1 is a diagram showing an overall configuration in an image forming apparatus according to a first embodiment. FIG. 1 shows an MFP 1 having a copy function, a print function, a scan function, and the like as an example of an image forming apparatus. The MFP 1 includes a paper feeding unit 2, an image forming unit 3, and an image reading unit 4.

The paper feed unit 2 includes paper feed cassettes 21 and 22 for storing recording papers of different sizes, and various rollers for transporting the recording paper stored in the paper feed cassettes 21 and 22 to the image formation position of the image forming unit 3. It has a paper feeding means 23.

The image forming unit 3 includes an exposure device 31, a photoconductor drum 32, a developing device 33, a transfer belt 34, and a fixing device 35. The image forming unit 3 exposes the photoconductor drum 32 by the exposure device 31 based on the image data of the original obtained by reading by the image reading device 10 described later in the image reading unit 4, and hides in the photoconductor drum 32. An image is formed, and a developing device 33 supplies toners of different colors to the photoconductor drum 32 for development. Then, the image forming unit 3 transfers the image developed on the photoconductor drum 32 by the transfer belt 34 to the recording paper supplied from the paper feeding unit 2, and then transfers the toner image transferred to the recording paper by the fixing device 35. The toner is melted and a color image is fixed on the recording paper.

FIG. 2 is a diagram showing an overall configuration in the image reading unit according to the first embodiment. The image reading unit 4 includes an image reading device 10 and an automatic document feeding device (ADF: Auto Document Feeder) 20.

The image reading device 10 includes a contact glass 11, a reference member 12, a light source 13, a first carriage 14, a second carriage 15, a lens 16, a sensor board 17, and a scanner motor 18. A line sensor 17a is provided on the sensor board 17. In the line sensor 17a, a plurality of image pickup elements such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal-Oxide Semiconductor) are arranged in one row or a plurality of rows.

Further, the contact glass 11 is a glass plate on which a document is placed. The reference member 12 is a white plate that serves as a reference for reading by the line sensor 17a. The reference member 12 is used when the white level of the line sensor 17a is adjusted and the shading process is performed. The reference member 12 may be a blackboard or the like instead of a white board. The light source 13 exposes a document and is a halogen lamp, a fluorescent lamp, a xenon lamp, an LED (Light Emitting Diode) or the like. The first carriage 14 holds the light source 13 and the first mirror 9a. The second carriage 15 holds the second mirror 9b and the third mirror 9c. The lens 16 forms an image of the document information on each image sensor of the line sensor 17a. The sensor board 17 is equipped with a line sensor 17a and performs photoelectric conversion and electrical processing. The scanner motor 18 is a motor for moving the first carriage 14 and the second carriage 15 to scan the document. The light emitted from the light source 13 is reflected by the document, then reflected in the order of the first mirror 9a, the second mirror 9b, the third mirror 9c, and the lens 16 to reach the line sensor 17a.

When the object to be read is a general document, the automatic document transfer device 20 is provided with a background portion that also serves as a presser for the general document when the general document to be scanned is scanned. The general documents are conveyed one by one from the automatic document transfer device 20, and the reflected light of the general documents exposed by the light source 13 when passing through the reading window 19 is folded back by the mirrors of the first carriage 14 and the second carriage 15. , A reduced image is formed on the light receiving surface of the line sensor 17a on the sensor board 17 through the lens 16.

When the object to be read is a general document or a special document, it is fixed on the contact glass 11 by the user. In the flatbed reading in which the document is read by scanning the first carriage 14 and the second carriage 15, the light source 13 arranged at the lower part of the contact glass 11 illuminates the reading target placed on the upper surface thereof, and the reading target is read. The illuminated illumination light is folded back by the mirrors of the first carriage 14 and the second carriage 15, and is reduced and imaged on the light receiving surface of the line sensor 17a on the sensor board 17 through the lens 16. At this time, the second carriage 15 moves at a speed V along the longitudinal direction of the reading target, and at the same time, the second carriage 15 moves at a speed of 1 / 2V, which is half the speed of the second carriage 15. Read the entire longitudinal direction of the reading target.

In the above configuration, the first carriage 14, the second carriage 15, the lens 16, the line sensor 17a, etc. including the mirror are separated, but a configuration using an integrated sensor module in which these are integrated is also possible. good.

<Main part composition>
Subsequently, the main part configuration of the present embodiment will be described with reference to FIG. Although the configuration of the image reading device 10 will be described here, the description of the paper feeding unit 2, the image forming unit 3, and the automatic document transporting device 20 will be omitted because they are the same as the conventional devices. FIG. 3 is a diagram showing an electrical configuration of an image reader according to the first embodiment.

The image reading device 10 of the present embodiment includes a signal generation unit 100, a capacitor 800, and an AFE 900. Of these, the signal generation unit 100 includes a photoelectric conversion unit 110, a charge / voltage conversion unit 120, an output unit 130, and a limiting unit 140.

The photoelectric conversion unit 110 is an element that converts light (reflected light from a document) into electrical energy (signal charge), and is composed of a linear image sensor in which a plurality of photoelectric conversion elements such as light emitting diodes are arranged one-dimensionally. Has been done.

The charge-voltage conversion unit 120 converts the voltage according to the amount of charge of the photoelectric conversion unit 110.

The output unit 130 is a circuit that outputs a signal of the voltage converted by the charge-voltage conversion unit 120 to the outside of the signal generation unit 100. The output unit 130 includes a capacitor 131, a reference voltage 132, and an amplifier circuit 133. Of these, the capacitor 131 stabilizes the voltage and removes noise. The reference voltage unit 132 supplies a reference voltage. The amplifier circuit 133 amplifies the voltage signal V _CCD out.

The limiting unit 140 is a circuit for limiting the voltage signal V _CCDout from the signal generation unit 100 so as not to exceed a predetermined level. This predetermined level is within the allowable input range of the signal processing unit connected to the subsequent stage of the signal generation unit 100. When the signal processing unit in the subsequent stage is AFE900, the predetermined level is set to a voltage at which the protection diode 910 described later does not turn ON when a signal is output from the signal generation unit 100 to the AFE900 in the subsequent stage. As a result, the limit range of the voltage signal width can be taken up to the input range limit of the AFE900.

Further, the limiting unit 140 is composed of a voltage generating unit 141 that generates a reference voltage and a signal limiting unit 142 that limits the signal amplitude after photoelectric conversion based on the reference voltage. As shown in FIG. 3, the signal limiting unit 142 is composed of a source follower circuit, the source side is the output unit 130, the gate side is the voltage generation unit 141, and the drain side is the power supply voltage unit 143. , Each is connected. The limiting unit 140 is an example of limiting means.

The capacitor 800 cuts the DC voltage component included in the voltage signal V _CCD out by AC-coupling the voltage signal V _CCD out of the signal generation unit 100. In this case, the voltage signal V _CCDout of the signal generation unit 100 is output to the AFE900, but since the operating voltage is different between the signal generation unit 100 and the AFE900, the capacitor 800 is AC-coupled. The capacitor 800 is an example of a cut portion.

The AFE900 is composed of a protection diode 910, various analog signal processing units 920, and an A / D conversion unit 930.

Of these, the protection diode 910 prevents the failure of the AFE900 by operating so as to keep the excessive signal within a certain range when the negative electrode excessive signal is input to the AFE900. For example, when an excessive signal is output from the signal generation unit 100 to the AFE 900 via the capacitor 800, the protection diode 910 shifts the level to the high voltage side to keep the excessive signal within a certain range.

The various analog signal processing units 920 process various analog signals before A / D conversion with respect to the voltage signal V _AFEin contained within a certain range by the protection diode.

The A / D conversion unit 930 A / D converts the analog signal processed by various analog signal processing units 920 into a digital signal (data), and outputs the digital signal (data) to the image forming unit 3 side. do. As a result, the image reading device 10 completes reading the image of the original.

<Processing method>
Subsequently, the processing method of the present embodiment will be described with reference to FIG. 4A and 4B relate to the first embodiment, FIG. 4A is a diagram showing the output voltage of the charge-voltage conversion unit, and FIG. 4B is a diagram in which the voltage of the voltage signal of the charge-voltage conversion unit is limited by the limiting unit. c) is a diagram showing the voltage signal of AFE, and (d) is a diagram showing the voltage signal of AFE when excessive light and normal light are incident on the photoelectric conversion unit.

When excessive light is incident on the photoelectric conversion unit 110, the output unit 130 outputs an excessive voltage signal VCCDout having an excessive amplitude Vovr with respect to the offset voltage Voff, as shown in FIG. 4A. do. Here, in the limiting unit 140, when the voltage difference between the gate and the source exceeds the threshold value voltage Vth of the MOSFET, the MOSFET is turned on. In this case, a current flows from the power supply connected to the drain, and the voltage signal VCCDout connected to the source side is limited to be VG-Vth. That is, as shown in FIG. 4B, when the signal width to be restricted by the limiting unit 140 is VLim, each of the limiting units 140 is such that the voltage signal VCCDout becomes VG-Vth = Voff-VLim. Set the circuit value in advance. Then, the limiting unit 140 limits the excessive voltage signal Vovr so that the protection diode 910 does not turn on at the input unit of the AFE900 in the subsequent stage. Thereby, as shown in FIG. 4C, the minimum voltage of the voltage signal VAFEin to the AFE900 can be limited so as not to fall below 0V at which the current starts to flow in the protection diode 910 of the AFE900.

In FIG. 3, the case where the limiting unit 140 is provided inside the signal generation unit 100 is taken as an example, but the same effect is exhibited even when the limiting unit 140 is provided outside the signal generation unit 100.

<Effect>
In the technique described in Patent Document 1, the voltage signal V _CCDout of the signal generation unit 1000 is similarly divided not only when the excessive light is incident but also when the normal light is incident. As a result, as shown in FIG. 16, the influence of noise on the voltage signal V _AFEin on the AFE900 becomes relatively large, so that the S / N ratio of the digital data (image data) output from the AFF9000 deteriorates. There was a problem that it would end up.

On the other hand, in the present embodiment, the voltage signal V is only when the limit unit 140 exceeds the predetermined level V _Lim for the signal width V _sig of this voltage signal with respect to the voltage signal V _CCD out of the output unit 130. _Limit the voltage on the CCD out. In this case, the predetermined level V _Lim is set based on the level at which the voltage signal from the signal generation unit 100 when the excessive light is incident on the photoelectric conversion unit 110 does not affect the AFE900 in the subsequent stage. There is no limit to the voltage signal V _CCD out at the time of incident. Therefore, the above-mentioned effect that the deterioration of the S / N ratio is not caused by the limitation of the image signal at the time of normal light incident is obtained.

From the above, as shown in FIG. 5D, when the reflected light is excessive light, the minimum voltage of the voltage signal V _AFEin to the AFE900 is 0V at which the current starts to flow in the protection diode 910 of the AFE900. It can be limited so that it does not fall below, and even if the light returns from excessive light to normal light, the voltage level of the voltage signal to the AFE900 does not gradually decrease for each line, preventing the occurrence of abnormal images. can do.

<Supplement>
In the first embodiment, since the offset voltage Voff of the voltage signal VCCDout is applied by the reference voltage in the output unit 130, there is a variation in the limitation due to the variation in the circuit of the output unit 130. Therefore, even if the value of each circuit of the limiting unit 140 is set in advance so that VG-Vth = Voff-VLim, the offset voltage Voff is set as shown in FIGS. 5A and 5B. The limiting unit 140 may not be limited to a desired amplitude due to a deviation from the applied voltage VG by the voltage generating unit 141. In FIG. 5, the solid line shows the case where there is no variation in the circuit, the broken line shows the case where there is variation in the circuit, (a) shows the minimum voltage VLim_min due to the variation in the circuit, and (b) shows the circuit. The maximum voltage VLim_max due to the variation of is shown.

Therefore, in the second embodiment described below, the problem of variation in limitation due to the variation in the circuit of the output unit 130 is solved.

[Second Embodiment]
Subsequently, the second embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 is an electrical configuration diagram showing a modified example of the signal generation unit according to the second embodiment. FIG. 7 is a diagram showing a voltage signal of the charge-voltage conversion unit when the invention of the second embodiment is used. The same components as those of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 6, the image reader 10 of the present embodiment includes a signal generation unit 200, a capacitor 800, and an AFE 900. The signal generation unit 200 includes a photoelectric conversion unit 110, a charge / voltage conversion unit 120, an output unit 130, and a limiting unit 240. Here, the limiting unit 240 is provided in place of the limiting unit 140 with respect to the first embodiment. The limiting unit 240 is an example of limiting means.

The same configuration as the reference voltage 132 and the part X1 of the amplifier circuit 133 is diverted as the voltage generation unit 241 in the limiting unit 240. That is, the voltage generation unit 241 (X1) is composed of a reference voltage 242 corresponding to the reference voltage 132 and an amplifier circuit 243 corresponding to the amplifier circuit 133. As a result, the voltage generation unit 241 generates the same voltage as the offset voltage applied in the partial configuration (X1) of the output unit 130. In this embodiment, circuits manufactured from the same wafer (base) utilize characteristics having similar variations.

<Effect>
As described above, in the image reader 10 of the second embodiment, even if the offset voltage V _off of the voltage signal V _CCD out varies due to the circuit variation of the output unit 130, the same voltage is generated in the voltage generation unit. It can also be generated by 241.

Therefore, it is possible to eliminate the deviation between the applied voltage V _G by the voltage generation unit, which is the reference of the limitation, and the offset voltage V _off of the voltage signal V _CCD out to be restricted, which has been a problem in the first embodiment. .. As a result, according to the configuration of the present embodiment, the accuracy of the limiting voltage can be improved and the amplitude can be limited to a desired value.

Further, in the limiting unit 240, the voltage V _Lim for which the amplitude is to be limited is determined by V _th . Therefore, when adjusting V _Lim arbitrarily, it is necessary to adjust V _th . As a means for arbitrarily adjusting V _Lim , a level shifter may be inserted between the voltage generation unit 241 and the gate portion of the source follower circuit to adjust the voltage to any voltage V _Lim .

From the above, the voltage V _Lim whose amplitude is desired to be limited falls between the voltages V _{G_min} -V _th and V _{off_min} as shown in FIG. 7 (a), and is as shown in FIG. 7 (b). In addition, the voltage falls between V _G -V _th and V _{off_max} . In FIG. 7, the solid line shows the voltage signal when the invention of the present embodiment is applied, and the broken line shows the voltage signal when affected by the variation of the circuit without applying the invention of the present embodiment. There is.

[Third Embodiment]
Subsequently, the third embodiment will be described with reference to FIGS. 8 and 9. FIG. 8 is an electrical configuration diagram showing a modified example of the signal generation unit according to the third embodiment. 9A and 9B relate to the third embodiment, FIG. 9A is a diagram showing a voltage signal of a signal generation unit and a voltage signal of AFE when there is no charge limitation, and FIG. 9B is a signal generation when there is a charge limitation. It is a figure which showed the voltage signal of the part and the voltage signal of AFE. The same components as those of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 8, the image reader 10 of the present embodiment includes a signal generation unit 300, a capacitor 800, and an AFE 900. The signal generation unit 300 includes a photoelectric conversion unit 110, a charge / voltage conversion unit 120, an output unit 130, and an OFD (Overflow Drain) 310. Here, with respect to the first embodiment, the limiting unit 140 is omitted, and an OFD 310 is newly provided. Here, in order to explain the photoelectric conversion unit 110 in detail, it is shown that the photoelectric conversion unit 110 is composed of a PD array (Photodiode Array) 111, a transfer gate 112, and an analog shift register 113. ..

The PD array 111 is a detector in which a type of light receiving element (PD) that converts an optical signal into a signal charge by absorbing light is arranged. The transfer gate 112 is a circuit that transfers the signal charge output by the PD array 111 to the analog shift register 113. The analog shift register 113 is a circuit that sequentially transfers signal charges to the charge-voltage conversion unit 120. Further, the OFD 310 is a circuit that discharges the signal charge overflowing from the transfer gate 112. The OFD 310 limits the excessive output from the photoelectric conversion unit 110 when the excessive light is incident.

For example, when there is no charge limitation due to the absence of OFD310, as shown in FIG. 5A, when the minimum voltage of the voltage signal V _AFEin falls below 0V due to excessive light incident, the voltage of the input section of the AFE900. Is level-shifted to the high voltage side so that the average voltage during the clamping period becomes 0V, and the image signal level at the time of normal light incident immediately after that is determined to be 0 (black) as digital data (Fig. 9 (Fig. 9). a) See).

On the other hand, in the present embodiment, the excess charge is discharged so that the amount of charge becomes a predetermined level by the OFD 310. This predetermined level is a level at which the protection diode 910 does not turn on at the input unit of the AFE900 in the subsequent stage when the voltage signal V _AFEin is input. That is, the minimum voltage of the voltage signal V _AFEin is limited so as not to fall below 0V at which the current starts to flow in the input protection diode 910 of the AFE900. As a result, the level shift of the voltage signal V _AFEin due to the incident of excessive light does not occur. Therefore, as in FIGS. 4 (b) and 4 (d), even if normal light is incident immediately after the incident of abnormal light, the photoelectric light is photoelectric. The conversion unit 110 can normally read the original. (See FIG. 9 (b)). The OFD 310 is an example of limiting means.

<Effect>
As described above, according to the third embodiment, it is possible to suppress the output of excess charge from the photoelectric conversion unit 110 to the charge-voltage conversion unit 120 when the excessive light is incident, and the excessive output to the AFE 900 is caused. It is possible to suppress the occurrence of abnormal images.

In FIG. 8, the case where the OFD 310 is connected to the transfer gate 112 is taken as an example, but it may be connected to the PD array 111 or the analog shift register 113, or between the photoelectric conversion unit 110 and the charge-voltage conversion unit 120. It may be provided.

[Fourth Embodiment]
Subsequently, the fourth embodiment will be described with reference to FIG. FIG. 10 is an electrical configuration diagram showing a modified example of the signal generation unit according to the fourth embodiment. The same components as those of the first and third embodiments are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 10, the image reader 10 of the present embodiment includes a signal generation unit 400, a capacitor 800, and an AFE 900. The signal generation unit 400 includes a photoelectric conversion unit 210, a charge / voltage conversion unit 120, an output unit 130, and a control unit 440. In the photoelectric conversion unit 210 of the present embodiment, in addition to the PD array 111, the transfer gate 112, and the analog shift register 113, a voltage-controlled transmittance variable filter 211 is provided on the light receiving surface side of the PD array 111. This voltage-controlled variable transmittance filter is composed of an organic photoelectric thin film. Further, the control unit 440 is a circuit that controls the transmittance of the transmittance variable filter according to the voltage signal from the charge-voltage conversion unit 120.

For example, when the light amount is not limited, when the minimum voltage of the voltage signal V _AFEin falls below 0V due to the incident of excessive light, the voltage at the input section of the AFE900 is high so that the average voltage during the clamping period becomes 0V. The level shifts to the side, and the image signal level at the time of normal light incident immediately after that is determined to be 0 (black) as digital data. (See FIG. 9 (a)).

On the other hand, in the present embodiment, the voltage-controlled transmittance variable filter 211 is provided in front of the PD array 111. Further, the control unit 440 controls the transmittance of the voltage control type transmittance variable filter 211 according to the voltage signal from the charge-voltage conversion unit 120, so that the amount of light incident on the PD array 111 becomes a predetermined level. Adjust so that. This predetermined level is a level at which the protection diode 910 does not turn on at the input unit of the AFE900 in the subsequent stage when the voltage signal V _AFEin is input. That is, the signal generation unit 400 limits the minimum voltage of the voltage signal V _AFEin so as not to fall below 0 V at which the current starts to flow in the input protection diode 910 of the AFE 900. As a result, the level shift of the voltage signal V _AFEin due to the incident of excessive light does not occur. Therefore, as in FIGS. 4 (b) and 4 (d), even if normal light is incident immediately after the incident of abnormal light, the photoelectric light is photoelectric. The conversion unit 110 can normally read the original. (See FIG. 9 (b)). The voltage-controlled transmittance variable filter 211 and the control unit 440 are examples of limiting means.

<Effect>
As described above, according to the fourth embodiment, it is possible to suppress the output of excess charge from the photoelectric conversion unit 110 to the charge-voltage conversion unit 120 when the excessive light is incident, and the excessive output to the AFE 900 is caused. It is possible to suppress the occurrence of abnormal images.

1 MFP (an example of an image forming apparatus)
10 Image reader 100 Signal generation unit 110 Photoelectric conversion unit 120 Charge / voltage conversion unit 130 Output unit 140 Restriction unit (example of limiting means)
141 Voltage generator 142 Signal limiter
143 Power supply voltage unit 210 Voltage control type transmittance variable filter (part of limiting means)
240 Restriction part (example of restriction means)
310 OFD (part of limiting means)
440 Control unit (part of limiting means)
800 capacitor (example of cut part)
900 AFE (an example of signal processing unit)

Japanese Unexamined Patent Publication No. 2014-27545

Claims (12)

A signal generation unit that receives the reflected light to be read and generates a voltage signal according to the amount of the reflected light.
A signal processing unit that performs signal processing to output the voltage signal to the image forming unit that forms an image, and a signal processing unit.
An image reading device that reads an image to be read by the present invention.
The signal generation unit includes limiting means for limiting the amplitude of the voltage signal so as not to exceed a predetermined level.
The limiting means is
A voltage generation unit that generates a reference voltage in the limiting means,
A signal limiting unit that limits the amplitude of the voltage signal to a predetermined level based on the reference voltage,
The image reading device is characterized in that the signal limiting unit comprises a single MOSFET. The image reading device according to claim 1, wherein the predetermined level is within an allowable input range of the signal processing unit. The image reading device according to claim 1 or 2, wherein the signal generation unit has a linear image sensor in which a plurality of photoelectric conversion elements are arranged one-dimensionally. The signal generation unit
A photoelectric conversion unit that receives the reflected light from the reading target and converts the optical signal related to the reflected light into a signal charge.
A charge-voltage conversion unit that converts a voltage signal having an amplitude corresponding to the amount of charge of the signal charge, and a charge-voltage conversion unit.
An output unit that outputs the voltage signal converted by the charge-voltage conversion unit to the outside of the signal generation unit , and an output unit.
Have,
The voltage generation unit has the same configuration as a part of the output unit, and is characterized in that it generates the same voltage as the offset voltage applied in the output unit according to any one of claims 1 to 3. The image reader of the description. The signal generation unit
A photoelectric conversion unit that receives the reflected light from the reading target and converts the optical signal related to the reflected light into a signal charge.
A charge-voltage conversion unit that converts a voltage signal having an amplitude corresponding to the amount of charge of the signal charge, and a charge-voltage conversion unit.
An output unit that outputs the voltage signal converted by the charge-voltage conversion unit to the outside of the signal generation unit , and an output unit.
Have,
The image reading device according to any one of claims 1 to 4, wherein the limiting means limits the signal charge output from the photoelectric conversion unit. The image reading device according to any one of claims 1 to 5, wherein the limiting means is composed of an overflow drain. The photoelectric conversion unit has a photodiode array.
The image reading device according to claim 4, wherein the limiting means limits the amount of light incident on the photodiode array. The limiting means is
A voltage-controlled variable transmittance filter provided on the light receiving surface side of the photodiode array to change the amount of light incident on the photodiode array,
A control unit provided in the signal generation unit and controlling the transmittance of the voltage-controlled transmittance variable filter according to the amplitude of the voltage signal from the charge-voltage conversion unit.
The image reading apparatus according to claim 4 or 5. The image reading device according to claim 8, wherein the voltage-controlled transmittance variable filter is composed of an organic photoelectric thin film. The image reading device according to any one of claims 1 to 9.
It has a cut section that cuts the DC voltage component included in the voltage signal generated by the signal generation section.
The signal processing unit is an image reading device, characterized in that the cut voltage signal is subjected to the signal processing for outputting to the image forming unit. A signal generation step that receives the reflected light to be read and generates a voltage signal according to the amount of the reflected light.
A signal processing step for performing signal processing for outputting the voltage signal to an image forming unit that forms an image, and
Is an image reading method for reading the image to be read by executing the above.
The signal generation step includes a process of limiting the amplitude of the voltage signal so as not to exceed a predetermined level, and also includes a process of limiting the amplitude of the voltage signal to a predetermined level or higher.
The limiting process is
The voltage generation process that generates the reference voltage in the limiting process, and the voltage generation process.
Signal limiting processing that limits the amplitude of the voltage signal to a predetermined level based on the reference voltage,
An image reading method, further comprising performing the signal limiting process with a single MOSFET. An image forming apparatus comprising the image reading apparatus according to any one of claims 1 to 10.

Images