JPH04248756A - Method and device for reading picture - Google Patents

Abstract

PURPOSE:To improve the resolution and to attain high speed read by reducing after-image or the like caused in the subscanning direction by a picture reader (image sensor) by means of charge storage method. CONSTITUTION:An auxiliary voltage generating circuit 22 which applies an auxiliary voltage Va of the counter polarity to a drive voltage Vd a little before the application of the drive voltage Vd is finished to a photodiode 14 is provided on a noninverting input terminal of an operational amplifier 24 amplifying an output current Io from the photodiode 14.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method and apparatus for reading an image, and more particularly to a method and apparatus for reading an image on a document such as a facsimile, an image scanner, a digital copying machine, and an electronic blackboard by a so-called charge accumulation method. Concerning improvements to equipment.

0002

[Prior Art] Conventionally, a charge coupled device (charge coupled device) is used in a document reading section of a facsimile machine or the like.
An image reading device with a reduction optical system using a CCD (device; CCD) was used. This image reading device is generally called an image sensor, and in recent years, a contact type image sensor that can read an image on a document at the same magnification has been used. This contact image sensor is constructed by forming a plurality of photoelectric conversion elements made of a semiconductor such as amorphous silicon a-Si on a substrate such as glass in a one-dimensional manner. , storage type matrix drive system, photoconductive matrix drive system, storage type direct drive system, and photoconductive direct drive system. In particular, the matrix drive method is widely adopted because it requires fewer switching elements than the direct drive method and can provide a compact and inexpensive image sensor.

A photoconductive matrix drive type image sensor is disclosed in, for example, Japanese Patent Laid-Open No. 100864/1983. In this image sensor, a sensor section is constructed by linearly arranging n×m light receiving elements (photoelectric conversion elements) in a row, and is divided into m blocks each having n light receiving elements. The structure is such that a voltage is sequentially applied in order to read the signals of the light receiving elements for each block. Furthermore, among these light receiving elements, the ones located in the same position in each block are commonly connected to an operational amplifier, which reads and amplifies the signals of each light receiving element for each block, and outputs them from a common output terminal. is configured to do so.

On the other hand, an image sensor using an accumulation type matrix drive method is disclosed in, for example, Japanese Patent Laid-Open No. 1-194654. A photodiode is used as a photoelectric conversion element in this image sensor, but since the photocurrent generated in this photodiode is weak, the image sensor is configured to detect the photocurrent using a so-called charge accumulation method.

[0005] Here, the storage type matrix drive system will be explained based on the drawings. In FIG. 13, reference numeral 1 indicates a photodiode as a photoelectric conversion element, and reference numeral 2 indicates a blocking diode. blocking diode 2
are connected in series to each photodiode 1 with opposite polarity to prevent crosstalk between the photodiodes 1. Further, reference numeral 3 is a drive voltage generating circuit as a drive voltage applying means that sequentially applies a drive voltage Vd to the anode terminal of each photodiode 1 via a blocking diode 2 for each block 4, and reference numeral 5 is an operational amplifier. This is a current amplification circuit.

First, when a negative drive voltage Vd is sequentially applied to each block 4 by the drive voltage generating circuit 3, the interelectrode capacitance of each photodiode 1 is sequentially charged. here,
The interelectrode capacitance refers to the electrostatic capacitance formed between the electrodes of the photodiode 1, and is a concept that includes junction capacitance. When the application of the driving voltage Vd is finished, each blocking diode 1 is placed in a reverse bias state, so that each interelectrode capacitance is discharged by a photocurrent generated according to the amount of incident light. This total discharge amount is equal to the amount of photodiode 1 within a certain period of time.
The accumulation time T is proportional to the total amount of light incident on the
It's called d. When the drive voltage Vd is applied to the photodiode 1 again by the drive voltage generation circuit 3 after discharging, the interelectrode capacitance is charged again, so that an output current Io flows from the cathode terminal of the photodiode 1. However, the output current I
Since the drive voltage Vd is a negative voltage, o becomes a negative current. Then, the output current Io is amplified by the current amplification circuit 5 to obtain the output voltage V1. This output voltage V1 is expressed by the following equation, where Rf is the negative feedback resistor. V1=-Io・Rf

Since the total amount of light incident on the photodiode 1 within the accumulation time Td is proportional to the time-integrated value of the output current Io, this output voltage V1 is time-integrated by an integrating circuit or the like to obtain an image signal. .

[0008]

However, in this storage type matrix drive system, the time for applying the drive voltage Vd to the photodiode 1 (hereinafter referred to as block selection time T)
It is called c. ) becomes short, there is a problem that an afterimage occurs in the sub-scanning direction. Such a phenomenon will be explained in detail based on FIG. 14. For example, assume that a white image 6 is read by a certain photodiode 1 in the n-th main scan, and a black image 7 is read in the n+1-th main scan. First, a large amount of light enters the photodiode 1 due to the white image 6, and after the inter-electrode capacitance of the photodiode 1 is discharged to a large extent, when the driving voltage Vd is applied to the photodiode 1, the inter-electrode capacitance of the photodiode 1 is The capacity is recharged. The output current Io associated with this charging is detected, and the white image 6 is read. Next, the black image 7 is read, but since no light is incident on the black image 7, the interelectrode capacitance is not discharged. Then, when the driving voltage Vd is applied to the photodiode 1 again, a small amount of output current Io flows even though the image 7 is black, and the output voltage V1
occurs (8). This appears as an afterimage. In other words, the cause of the afterimage is that the interelectrode capacitance is not fully charged because the block selection time Tc is short (9), and when the next black image 7 is read and the drive voltage Vd is applied, it was not fully charged last time. Output current Io to replenish the minute
This is because it flows. There is a problem in that the afterimage reduces the resolution in the sub-scanning direction and makes the image unclear. Particularly, in devices that read multi-gradation images such as photographs, the gradation of the density changes or the density becomes uneven, which has become a serious problem.

In order to solve this problem, the interelectrode capacitance is sufficiently charged by increasing the block selection time Tc or by applying the drive voltage Vd to the photodiode 1 for a certain period of time within the storage time Td. Various measures have been taken to restore the state, but there are problems such as high-speed reading is not possible and the drive circuit is complicated and costly.

[0010] Therefore, the present inventors reduced the afterimage etc.
As a result of intensive research to enable high-speed reading, the present invention was achieved.

[0011]

[Means for Solving the Problems] The gist of the image reading method according to the present invention is to charge the inter-electrode capacitance of a photoelectric conversion element, and to input the charged inter-electrode capacitance into the photoelectric conversion element. After discharging for a certain period of time by a photocurrent generated according to the amount of light, the discharged interelectrode capacitance is charged by applying a driving voltage to one end of the photoelectric conversion element for a certain period of time. In the method of reading an image by time-integrating the output current flowing from the other end of the photoelectric conversion element, before finishing applying the drive voltage, the photoelectric conversion element is The purpose is to change the voltage at the other end of the conversion element.

Further, in this image reading method, the image is read by time-integrating the output current flowing before changing the voltage at the other end of the photoelectric conversion element.

On the other hand, the gist of the image reading device according to the present invention is that it includes a photoelectric conversion element that generates a photocurrent depending on the amount of incident light, and a drive voltage that applies a drive voltage to one end of the photoelectric conversion element for a certain period of time. In an image reading device comprising an applying means and an output amplifying means for time-integrating an output current flowing from the other end of the photoelectric conversion element when the driving voltage is applied for a certain period of time, before the application of the driving voltage ends. Another feature is that an auxiliary voltage applying means is provided for changing the voltage at the other end of the photoelectric conversion element so that the voltage applied to both ends of the photoelectric conversion element becomes higher.

[0014] Furthermore, in this image reading device, the output amplifying means is configured to time-integrate the output current flowing before the voltage at the other end of the photoelectric conversion element is changed.

Furthermore, in such an image reading device, the output amplifying means is comprised of an operational amplifier, the other end of the photoelectric conversion element is connected to the inverting input terminal of the operational amplifier, and the auxiliary voltage applying means is connected to the inverting input terminal of the operational amplifier. It is connected to the non-inverting input terminal.

[0016]

According to the image reading method of the present invention, the inter-electrode capacitance of the photoelectric conversion element is charged, and the charged inter-electrode capacitance is discharged for a certain period of time by a photocurrent generated in accordance with the amount of incident light. Next, when a driving voltage is applied to one end of the photoelectric conversion element, the discharged interelectrode capacitance begins to be charged again. Then, just before the drive voltage is finished being applied, the voltage at the other end of the photoelectric conversion element is changed to increase the voltage applied to both ends of the photoelectric conversion element, and the interelectrode capacitance of the photoelectric conversion element is rapidly charged and immediately Returns to fully charged initial state. An image is read by integrating the output current flowing while a driving voltage is applied to one end of the photoelectric conversion element over time. Next, after being discharged for a certain period of time by a photocurrent generated according to the amount of incident light, a driving voltage is similarly applied to charge the interelectrode capacitance, but the interelectrode capacitance is temporarily returned to its initial state. Therefore, no current flows to charge the battery that was not fully charged when the drive voltage was applied last time, and there is no possibility that an afterimage will occur, the density tone will change, or the density will become uneven. do not have.

Furthermore, by reading the image by integrating the output current flowing before the voltage at the other end of the photoelectric conversion element is changed over time, the influence of the current flowing after the voltage is changed can be reduced. The image can be read accurately without any interference.

On the other hand, according to the image reading device according to the present invention, the drive voltage applying means applies a drive voltage to one end of the photoelectric conversion element, and the interelectrode capacitance of the photoelectric conversion element is charged. Then, the charged interelectrode capacitance is discharged for a certain period of time by a photocurrent generated according to the amount of light incident on the photoelectric conversion element. Next, when a driving voltage is applied to one end of the photoelectric conversion element by the driving voltage applying means, the discharged interelectrode capacitance starts to be charged again. after that,
Before the application of the driving voltage is finished, the voltage at the other end of the photoelectric conversion element is changed by the auxiliary voltage application means to increase the voltage applied to both ends of the photoelectric conversion element, and the interelectrode capacitance of the photoelectric conversion element is rapidly charged. , it is quickly returned to its initial state. An output current flowing while a driving voltage is applied to one end of this photoelectric conversion element is time-integrated by an output amplifying means, and an image is read. After the inter-electrode capacitance is discharged for a certain period of time by the photocurrent again, a driving voltage is applied by the driving voltage applying means to charge the inter-electrode capacitance, but the inter-electrode capacitance is once returned to the initial state by the auxiliary voltage applying means. Since the battery has been reset, no current flows to charge the amount that could not be fully charged when the drive voltage was previously applied by the drive voltage applying means, and no afterimage or the like occurs.

Furthermore, since the output current that flows before the voltage at the other end of the photoelectric conversion element is changed by the auxiliary voltage applying means is time-integrated and the image is read, the influence of the current that flows after the voltage is changed is The image is read accurately without any interference.

Furthermore, before the drive voltage application means finishes applying the drive voltage, the auxiliary voltage application means changes the voltage applied to the non-inverting input terminal of the operational amplifier constituting the output amplification means, and the voltage applied to the non-inverting input terminal of the operational amplifier forming the output amplifying means is changed. The voltage at the terminals is also changed to the same potential, increasing the voltage applied across the photoelectric conversion element, rapidly charging the interelectrode capacitance of the photoelectric conversion element, and similarly reducing afterimages.

[0021]

Embodiments Next, embodiments of the image reading apparatus and reading method according to the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the image reading device according to the present invention includes a plurality of photodiodes 14 divided into blocks 12 and a plurality of blocking diodes 16 connected in series with the photodiodes 14 with opposite polarity. 16 is connected to a drive voltage generating circuit 18 for each block 12, and on the other hand, each photodiode 14 is connected to an inverting input terminal of an operational amplifier 20, with the photodiodes 14 located at the same position common to each block 12. Further, an auxiliary voltage generating circuit 22 is connected to the non-inverting input terminals of these operational amplifiers 20, and each output terminal 23 of the operational amplifiers 20 is connected to an integrating circuit 26 as shown in FIG. There is.

The photodiode 14 is made of a semiconductor such as amorphous silicon a-Si, and is a photoelectric conversion element that generates a photocurrent depending on the amount of incident light. On the other hand, the blocking diode 16 is the photodiode 14
This is to prevent crosstalk between the photodiode 14 and the amorphous silicon a-S
It is formed from a semiconductor such as i. Further, the drive voltage generation circuit 18 is composed of an LSI or the like having a built-in shift register, etc., and this drive voltage generation circuit 18 applies a negative drive voltage Vd to the anode terminal of the photodiode 14 via the blocking diode 16 to each block. This is a driving voltage applying means for sequentially applying the voltage every 12 times. operational amplifier 20
A negative feedback resistor Rf is connected in parallel to the current amplifier circuit 2 which amplifies the output current Io of the photodiode 14.
4 are configured. In addition, the auxiliary voltage generation circuit 22 generates an auxiliary voltage Va of the opposite polarity to the drive voltage Vd, that is, a positive one, to the operational amplifier 20 shortly before the drive voltage generation circuit 18 finishes applying the drive voltage Vd to each photodiode 14 . The signal is configured to be applied to the inverting input terminal.

As shown in FIG. 2, the integrating circuit 26 consists of an operational amplifier 28, and a switching element 30 is connected in parallel to the integrating capacitor Ci. This switching element 30 is configured to reset the integrating capacitor Ci at the same time when the auxiliary voltage Va is applied by the auxiliary voltage generation circuit 22 to the non-inverting input terminal of the operational amplifier 20. In this example, the current amplifying circuit 24 and the integrating circuit 26 constitute an output amplifying means for time-integrating the output current of the photodiode 14.

Next, the operation for one channel in this image reading apparatus will be explained based on the time chart shown in FIG. A negative drive voltage Vd is applied by the drive voltage generation circuit 18 to the blocking diode 16 in the forward direction and to the photodiode 14 in the reverse direction. That is, when the driving voltage Vd is applied to the blocking diode 16
The voltage is applied to the anode terminal of the photodiode 14 via the photodiode 14. By applying such a driving voltage Vd for a certain period of time, the interelectrode capacitance of the photodiode 14 is completely charged. Then, light corresponding to an image is made incident on the photodiode 14 for a certain period of time, and the interelectrode capacitance is discharged by a certain certain amount by a photocurrent generated according to the amount of light. Next, when the drive voltage generation circuit 18 applies the drive voltage Vd to the photodiode 14 again, the interelectrode capacitance starts to be charged again. At this time, a negative output current Io flows from the cathode terminal of the photodiode 14, and this output current Io is amplified by the current amplification circuit 24 to obtain an output voltage V1. This output voltage V1 is expressed by the following equation. V1=-Io・Rf

Furthermore, this output voltage V1 is time-integrated by an integrating circuit 26 to obtain an output voltage Vo. This output voltage Vo is expressed by the following equation. Vo=Rf/(Ri・Ci)・∫Iodt

[0026]
Thereafter, shortly before the drive voltage generation circuit 18 finishes applying the drive voltage Vd, the switching element 30 resets the integrating capacitor Ci, and at the same time, the auxiliary voltage generation circuit 22 applies the auxiliary voltage to the non-inverting input terminal of the operational amplifier 20. Va is applied. When the auxiliary voltage Va is applied, the voltage at the inverting input terminal is also changed to approximately the same potential as this auxiliary voltage Va. Since the applied auxiliary voltage Va has the opposite polarity to the drive voltage Vd, that is, it is a positive voltage, the voltage applied across the photodiode 14 becomes high, and the interelectrode capacitance is rapidly charged.

Next, assume that a black image is to be read. In the black image, almost no light enters the photodiode 14, so the interelectrode capacitance is not discharged at all. Therefore, even if the drive voltage Vd is applied to the photodiode 14 again, the interelectrode capacitance remains charged, so no output current Io flows at all. In other words, even if the previous image was white and the interelectrode capacitance of the photodiode 14 was almost discharged, the next image is always read with the interelectrode capacitance fully charged. As described in the technical section, an excess output current Io does not flow, and an afterimage does not occur in the sub-scanning direction or the density gradation is not changed. Further, at the same time that the auxiliary voltage Va is applied to the non-inverting input terminal of the operational amplifier 20, the integrating capacitor Ci is reset by the switching element 30, so the output voltage Vo immediately becomes 0V, and the auxiliary voltage Va is applied. It is not affected by the output current Io that flows later.

As described above, since the image reading apparatus according to the present invention is provided with the auxiliary voltage generating circuit 22, it is possible to obtain a clear image without afterimages. Furthermore, since the switching element 30 is configured to reset the integrating capacitor Ci at the same time when the auxiliary voltage Va is applied to the non-inverting input terminal of the operational amplifier 20, the output current Io that flows after the auxiliary voltage Va is applied. Images can be read accurately without being affected by Furthermore, an auxiliary voltage generation circuit 22 is added to the existing image reading device,
Since the switching element 30 is simply configured to be activated in synchronization with the auxiliary voltage Va, an inexpensive and high-performance image reading device can be provided.

Although one embodiment of the image reading apparatus according to the present invention has been described above in detail, the present invention is not limited to the above-described embodiment, and can be implemented in other embodiments. For example, as shown in FIG. 4, an auxiliary current generation circuit 34 may be connected to the inverting input terminal of the operational amplifier 32. The auxiliary current generating circuit 34 is configured to generate the auxiliary current Ia shortly before the driving voltage generating circuit 36 finishes applying the negative driving voltage Vd to the photodiode 40 via the blocking diode 38. In this case, shortly before the drive voltage generation circuit 36 finishes applying the drive voltage Vd, the auxiliary current generation circuit 34 causes the auxiliary current Ia to flow into the photodiode 40, and the interelectrode capacitance is rapidly charged, resulting in an afterimage, etc. Does not occur. In this example, as a result of the auxiliary current Ia flowing into the photodiode 40 by the auxiliary current generation circuit 34, the voltage applied to the photodiode 40 increases and the voltage applied to the photodiode 40 increases.
The voltage at the cathode terminal of 0 is being changed. That is, the auxiliary current generation circuit 34 controls the photoelectric conversion element (40) so that the voltage applied to both ends of the photoelectric conversion element (40) becomes high before the driving voltage is applied to one end of the photoelectric conversion element (40). This is an auxiliary voltage applying means for changing the voltage at the other end.

Further, as shown in FIG. 5, when an integrating circuit 44 is connected which directly integrates the output current Io from the photodiode 42 over time without converting it into a voltage, the integrating circuit 44 is configured as follows. The auxiliary voltage generation circuit 48 may be connected to the non-inverting input terminal of the operational amplifier 46 that performs the operation. Further, as described above, the switching element 50 may be configured to reset the integrating capacitor Ci at the same time that the auxiliary voltage Va is applied to the non-inverting input terminal of the operational amplifier 46 by the auxiliary voltage generating circuit 48. Good. In this example, the integrating circuit 44 is an output amplifying means that time-integrates the current flowing to the other end of the photoelectric conversion element (42).

Furthermore, as shown in FIG. 6, the cathode terminal of the photodiode 54 may be connected via a switching element 56 to an auxiliary voltage Va having a polarity opposite to that of the drive voltage Vd. The switching element 56 may be configured to be in a closed state shortly before the drive voltage generation circuit 58 finishes applying the drive voltage Vd to the photodiode 54 .

Further, as shown in FIG. 7, the cathode terminal of the photodiode 60 is connected to the operational amplifier 6 via a resistor R1.
2, its cathode terminal may be connected to the auxiliary voltage Va having the opposite polarity to the drive voltage Vd via the switching element 64 and the resistor R2. This switching element 64 is configured similarly to the switching element 56 described above. In this example, the switching element 64 is activated shortly before the drive voltage generation circuit 66 finishes applying the drive voltage Vd, and the voltage applied across the photodiode 60 is increased, and the interelectrode capacitance is rapidly charged. It is. Here, the resistor R2 is for preventing a rush current flowing into the interelectrode capacitance of the photodiode 60 at the moment the switching element 64 is activated. As is clear from this example,
It is also possible to configure the operational amplifier 62 so that the voltages at the inverting input terminal and the non-inverting input terminal are always at zero potential. That is, the configuration may be such that at least the voltage at the cathode terminal of the photodiode 60 can be changed.

Furthermore, the voltages at the inverting input terminal and the non-inverting input terminal of the operational amplifier can be set to arbitrary potentials. For example, as shown in FIG. 8, a reference voltage generation circuit 70 changes the reference voltage Vref so that the voltage applied across the photodiode 68 becomes higher shortly before the drive voltage generation circuit 67 finishes applying the drive voltage Vd. It may be connected to the non-inverting input terminal of the operational amplifier 72. This reference voltage generation circuit 70 is an auxiliary voltage applying means that changes the voltage at the other end of the photoelectric conversion element (68) so that the voltage applied to both ends of the photoelectric conversion element (68) increases before the application of the driving voltage Vd is finished. It is.

By the way, when the rectangular auxiliary voltage Va is applied to the non-inverting input terminal of the operational amplifier by the auxiliary voltage generation circuit, spike noise may occur at the rise and fall of the rectangular auxiliary voltage Va. Therefore, as shown in FIG. 9, the auxiliary voltage generating circuit 22 may be connected to the non-inverting input terminal of the operational amplifier 20 via a time constant circuit 74 consisting of a resistor Rt and a capacitor Ct. In this example, as shown in the time chart of FIG. 10, the rise and fall of the auxiliary voltage Va applied to the non-inverting input terminal of the operational amplifier 20 are slowed, and spike noise is reduced. Therefore, an output voltage Vo with a better SN ratio can be obtained.

Alternatively, as shown in FIG. 11, the auxiliary voltage V
A reverse voltage generation circuit 76 that generates a voltage Va1 having a polarity opposite to that of a.
It is also good to connect in parallel with the auxiliary voltage generation circuit 22 via the capacitor Cd. In this example, as shown in the time chart of FIG. 12, even if the auxiliary voltage Va accompanied by the spike noise 78 is applied to the non-inverting input terminal of the operational amplifier 20, the auxiliary voltage Va with the spike noise 78 is applied to the non-inverting input terminal of the operational amplifier 20. A voltage Va2 obtained by differentiating the auxiliary voltage Va is applied, and the spike noise 78 is reduced. Vad is a voltage obtained by combining the auxiliary voltage Va and its differential voltage Va2. Therefore, as described above, an output voltage Vo with a good SN ratio can be obtained.

Although the drive voltage Vd in the embodiments described above is a negative voltage, it can also be a positive voltage. In this case, the photodiode and the blocking diode may be connected in opposite directions. . Further, the auxiliary voltage Va applied by the auxiliary voltage generation circuit also needs to have a reverse polarity, that is, a negative voltage. Furthermore, the aforementioned auxiliary current generation circuit 34 may be configured to generate a negative auxiliary current Ia.

Furthermore, the timing when the auxiliary voltage Va is applied to the non-inverting input terminal of the operational amplifier by the auxiliary voltage generation circuit is as follows.
It may be set appropriately depending on the values of the drive voltage Vd, interelectrode capacitance, block selection time Tc, etc. Furthermore, the switching element connected in parallel to the integrating capacitor is configured to reset the integrating capacitor a little before the auxiliary voltage Va is applied to the non-inverting input terminal of the operational amplifier by the auxiliary voltage generating circuit. Also good.

In addition, the present invention can be applied to an image reading device that is selectively driven by a TFT or the like instead of a blocking diode, and is further applicable to image reading devices such as a direct drive method without being limited to a matrix drive method. The present invention can be implemented with various improvements, modifications, and variations based on the knowledge of those skilled in the art without departing from the spirit thereof, such as being applicable to devices.

[0039]

Effects of the Invention In the image reading method according to the present invention, before finishing applying a driving voltage to one end of the photoelectric conversion element, the voltage at the other end of the photoelectric conversion element is increased so that the voltage applied to both ends of the photoelectric conversion element becomes high. Since the interelectrode capacitance is changed, the interelectrode capacitance is rapidly charged and the afterimage is reduced. therefore,
The resolution in the sub-scanning direction is increased and a clear image can be obtained. Furthermore, since the application time of the driving voltage can be shortened, high-speed reading becomes possible. Furthermore, in a device that reads multi-tone images such as photographs, the gradation of densities will not be read as different gradations, and furthermore, there will be no density unevenness, and an image that is more similar to a photograph can be obtained.

Furthermore, by reading the image by time-integrating the output current that flows before changing the voltage at the other end of the photoelectric conversion element, it is possible to read the image by time-integrating the output current that flows before changing the voltage at the other end of the photoelectric conversion element. images can be read accurately.

On the other hand, since the image reading device according to the present invention is provided with an auxiliary voltage applying means, the voltage applied to both ends of the photoelectric conversion element increases before the drive voltage is applied to one end of the photoelectric conversion element. The voltage at the other end of the photoelectric conversion element is changed, and the interelectrode capacitance is rapidly charged, thereby reducing afterimages and the like. Similarly, clear images can be obtained and high-speed reading is possible.

Furthermore, by configuring the output amplifying means to time-integrate the output current flowing before the voltage at the other end of the photoelectric conversion element is changed, the image can be read accurately.

Furthermore, the output amplifying means is composed of an operational amplifier, the other end of the photoelectric conversion element is connected to the inverting input terminal of the operational amplifier, and the auxiliary voltage applying means is connected to the non-inverting input terminal of the operational amplifier. By doing so, it is possible to provide an inexpensive and high-performance image reading device by simply adding a simple circuit to the existing image reading device.

[0044]

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of an image reading device according to the present invention.

FIG. 2 is a circuit diagram showing one channel extracted from the image reading device shown in FIG. 1;

FIG. 3 is a time chart showing the operation for one channel shown in FIG. 2;

FIG. 4 is a circuit diagram showing another embodiment of the image reading device according to the present invention.

FIG. 5 is a circuit diagram showing another embodiment of the image reading device according to the present invention.

FIG. 6 is a circuit diagram showing another embodiment of the image reading device according to the present invention.

FIG. 7 is a circuit diagram showing another embodiment of the image reading device according to the present invention.

FIG. 8 is a circuit diagram showing another embodiment of the image reading device according to the present invention.

FIG. 9 is a circuit diagram showing another embodiment of the image reading device according to the present invention.

FIG. 10 is a time chart showing the operation for one channel shown in FIG. 9;

FIG. 11 is a circuit diagram showing another embodiment of the image reading device according to the present invention.

FIG. 12 is a time chart showing the operation for one channel shown in FIG. 11;

FIG. 13 is a circuit diagram showing an example of a conventional image reading device.

14 is a time chart showing the operation for one channel in the image reading device shown in FIG. 13. FIG.

[Explanation of symbols]

12; Blocks 14, 40, 42, 54, 60; Photodiodes (photoelectric conversion elements) 16, 38; Blocking diodes 18, 36, 58, 66; Drive voltage generation circuit (drive voltage application means) 20, 28, 32, 46, 62, 72; operational amplifier 22
, 48, 70; Auxiliary voltage generation circuit (auxiliary voltage application means) 34; Auxiliary current generation circuit (auxiliary voltage application means) 24; Current amplification circuit 26; Integration circuits 30, 50; Switching element 44; Integration circuit (output amplification means) ) Vd; Drive voltage Va; Auxiliary voltage Io; Output current Vo; Output voltage

Claims (5)

[Claims] Claim 1: After charging the interelectrode capacitance of a photoelectric conversion element and discharging the charged interelectrode capacitance for a certain period of time by a photocurrent generated according to the amount of light incident on the photoelectric conversion element, By applying a driving voltage to one end of the photoelectric conversion element for a certain period of time, the discharged interelectrode capacitance is charged, and at the same time, by time-integrating the output current flowing from the other end of the photoelectric conversion element. An image reading method characterized in that, before finishing applying the drive voltage, the voltage at the other end of the photoelectric conversion element is changed so that the voltage applied to both ends of the photoelectric conversion element becomes higher. . 2. The image reading method according to claim 1, wherein the image is read by time-integrating the output current flowing before changing the voltage at the other end of the photoelectric conversion element. 3. A photoelectric conversion element that generates a photocurrent in accordance with the amount of incident light; a drive voltage applying means that applies a drive voltage to one end of the photoelectric conversion element for a certain period of time; and when the drive voltage is applied for a certain period of time. and an output amplifying means for time-integrating the output current flowing from the other end of the photoelectric conversion element, before the drive voltage is finished being applied,
An image reading device characterized in that an auxiliary voltage applying means is provided for changing the voltage at the other end of the photoelectric conversion element so that the voltage applied to both ends of the photoelectric conversion element becomes higher. 4. The output amplifying means is configured to time-integrate the flowing output current before the voltage at the other end of the photoelectric conversion element is changed. image reading device. 5. The output amplifying means comprises an operational amplifier, the other end of the photoelectric conversion element is connected to an inverting input terminal of the operational amplifier, and the auxiliary voltage applying means is connected to a non-inverting input terminal of the operational amplifier. The image reading device according to claim 3 or 4, characterized in that: