JPH0134494B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoelectric conversion device used in facsimile, OCR, and the like.

Conventionally, MOS image sensors and CCD image sensors have been widely used in photoelectric conversion devices such as facsimiles and OCR. These image sensors are manufactured using IC technology, so their size is about 2 to 3 cm, and in order to read the document surface,
It is necessary to reduce the size using an optical system having an object-to-image distance of 30 cm to 40 cm, making it difficult to miniaturize the device. In recent years, amorphous or polycrystalline thin films have been used,
By manufacturing a large image sensor that corresponds to the width of the document on a one-to-one basis, and performing photoelectric conversion by combining this with a focusing fiber array, we will reduce the object-image distance from several centimeters to more than ten centimeters and make it more compact. Attempts are being made to do so.

However, this photoelectric conversion device using a large image sensor has a drawback in that it is scan-driven. This will be explained below. FIG. 1 shows an example of a driving method for a large image sensor that has been tried in the past, and has a matrix configuration. In the figure, R ₁ , R ₂ ,
R ₃ ...R _o is a photoconductive element array formed of CdS, amorphous silicon, etc., D ₁ , D ₂ , D ₃ ...D _o
are blocking diode arrays to prevent current backflow, SX ₁ , SX ₂ , ... SX _n are selection switch arrays for the common side electrodes of the matrix, SY ₁ , SY ₂ ...
... _SY5 is a row of selection switches for individual side electrodes of the matrix, R _L is a load resistance for detecting photoconductive current, E is a DC power supply, and 1 is a signal output terminal.

Next, the operation will be explained. Common-side electrode selection switch row SX ₁ , SX ₂ ...one of SX _n and individual-side electrode selection switch row SY ₁ , SY ₂ , SY ₃ ,
Any photoconductive element can be selected by closing one of SY ₄ and SY ₅ . For example, when selecting the photoconductive element R ₁ , by closing the switch SX ₁ and the switch SY ₁ , the DC power supply E selects the selection switch SX ₁ -blocking diode _D1 -photoconductive element R1 _. ~Selection switch
Current flows through the load resistor R _L through the path of SY ₁ .
At this time, the conductivity of the photoconductive element _R1 changes depending on the amount of light incident on the photoconductive element _R1 , so the resistance value of the load resistor R _L should be set sufficiently smaller than the resistance value of the photoconductive element _R1 . As a result, a current approximately proportional to the amount of incident light flows through the load resistor R _L , and an output signal can be obtained from the signal output terminal 1. If the blocking diodes D ₁ , D ₂ ...D _o do not exist, an unnecessary current other than the current flowing through the photoconductive element R ₁ flows through the load resistor _R
The output signal is no longer proportional to the amount of incident light. for example,
In Figure 1, if all blocking diodes are short-circuited, each photoconductive element
In addition to the R ₁ to R _L route, the R ₂ to _{R 7} to R ₆ to R _L route, R ₂
~R _o-3 ~ _{R o-4} ~ _{R L} path, R ₃ ~R ₈ ~R ₆ ~ _{R L} path, R ₃ ~ _{R o-2} ~ _{R o-4} ~ _{R L} path, etc. Unnecessary current flows through the load resistance R _L through the path.
The blocking diode array serves to prevent these unnecessary currents from flowing. For this blocking diode, a high-performance diode chip with low reverse current is connected in series with each photoconductive element, or a diode chip with good blocking characteristics is used between the common electrode and the photoconductive element. A method is used to form a blocking diode in one piece using materials. In the former case, the structure is complicated and it is difficult to achieve high density. In the latter case, there are examples in which CdS is used for the photoconductive element and tellurium is used for the common electrode. Not only are the materials available for the diode limited, it is difficult to create good diode characteristics with sufficiently small forward resistance and reverse current, and blocking characteristics may become incomplete when light enters the diode. There are drawbacks.

Furthermore, in the conventional photoelectric conversion device shown in _FIG .
(need to be reduced to 1/50), but also had the disadvantage that the output signal level was low.

This invention was made to eliminate the drawbacks of the conventional photoelectric conversion device as described above, and by using an operational amplifier in the detection section of the photoelectric conversion signal, the blocking diode that was conventionally required can be eliminated. Therefore, the present invention provides a photoelectric conversion device that is simple in structure and easy to increase in density.

An embodiment of the present invention will be described below with reference to FIG. In FIG. 2, 1 is a signal output terminal, 2 is an operational amplifier, the positive input terminal of which is grounded, and the negative input terminal connected to the common side electrode selection switch SX ₁ ,
SX ₂ ...Connected to SX _n and load resistance R _L
It is connected to the output terminal of the operational amplifier via.
In addition, a selection switch SY ₁ connected to the individual side electrode,
SY ₂ ... SY ₅ are designed so that the individual side electrodes can be connected to either the DC power supply E or the ground.

Next, the operation will be explained. One of the common side electrode selection switch rows SX ₁ , SX ₂ , ...SX _n and the individual side electrode selection switch rows SY ₁ , SY ₂ ...
Select any photoconductive element by closing one of SY ₅ . This is the same operation as in FIG. The reason why the operation of the embodiment shown in FIG. 2 is superior to the conventional operation shown in FIG. 1 is that when an arbitrary photoconductive element is selected, the load resistance R _L is , no unnecessary current flows,
Therefore, there is no need for a blocking diode as shown in FIG. This will be explained in detail below.

In the embodiment of FIG. 2, for example, a photoconductive element
Consider the case where R ₁ is selected. Regarding the selection switches connected to the individual side electrodes, switch SY ₁ to the DC power supply E side, and switch the selection switches other than SY ₁ to the ground side. Also, regarding the selection switch connected to the common side electrode, only SY ₁ is kept closed. At this time, a current flows from the DC power source E to the load resistor R _L through the photoconductive element R ₁ . Since the load resistance R _L is connected between the output terminal and the negative input terminal of the operational amplifier 2, the operational amplifier 2 operates as an amplifier with R _L as a return resistance. At this time, operational amplifier 2
Since the positive input terminal of is grounded, the negative input terminal also has a value extremely close to the ground potential (about several mV). Therefore, the current value flowing through the photoconductive element _R1 is:
It is a value obtained by dividing the voltage of the DC power source E by the resistance value of the photoconductive element _R1 , and this value is proportional to the amount of light incident on the photoconductive element _R1 . On the other hand, since the selection switches SY ₂ , SY ₃ , SY ₄ , SY ₅ connected to the individual side electrodes are switched to the ground side, the photoconductive elements R ₂ , R ₃ ,
Both ends of R ₄ and R ₅ are at ground potential, so no current flows. Therefore, the same current as the current flowing through the photoconductive element _R1 flows through the load resistor R _L , and a photoelectric conversion output signal proportional to the amount of incident light can be obtained from the signal output terminal 1. photoconductive element
It operates in exactly the same way when a photoconductive element other than R ₁ is selected. Furthermore, since one switch on the common electrode side or the individual electrode side only needs to be an open/close switch (one transistor element), the number of circuit elements can be further reduced compared to the conventional case where all the switches are changeover switches (two transistor elements).

In the conventional example shown in Fig. 1, since the load resistor R _L is connected in series with the photoconductive element, the signal output voltage is not proportional to the amount of light incident on the photoconductive element in principle, and the load resistor R L is connected in series with the photoconductive element. If the resistance value of _L is set to be sufficiently smaller than the resistance value of the photoconductive element so that it is approximately proportional to the amount of incident light, there is a drawback that the magnitude of the signal output voltage becomes small. In the embodiment of the present invention shown in FIG. 2, the output signal voltage is not only proportional to the amount of light incident on the photoconductive element in principle, but also has the advantage of eliminating the need for a blocking diode _. By selecting a large resistance value, the signal voltage can be increased and the switch configuration can be simplified, which is a great advantage.

In the embodiment shown in FIG. 2, the operational amplifier 2 is connected to the selection switch row of the common side electrode of the matrix, and the selection switch of the individual side electrode can be connected to either the DC power supply E or the ground. Although the configuration has been shown, this configuration can be realized with various modifications. FIG. 3 shows a second embodiment of the present invention, in which a part of the configuration of FIG. 2 is modified, in which selection switches SX ₁ , SX ₂ . . _.
can be connected to either the negative input terminal of the operational amplifier 2 or the ground, and the individual side electrode selection switches SY ₁ , SY ₂ ...SY ₅ are configured to be connected to the DC power supply E. This is what I did. FIG. 3 shows the state of the selection switch row that selects photoconductive element R ₁ , but in this case as well, as is clear from the figure, both ends of photoconductive elements R ₂ , R ₃ , R ₄ , and R ₅ are Since it is at ground potential, no current flows, and the operation is the same as that of the embodiment shown in FIG.

Furthermore, FIG. 4 shows a third embodiment of the present invention, which has a configuration in which the positions of the operational amplifier 2 and the DC power source E are reversed in the embodiment of FIG. The same operation as in Fig. 3 is performed.

Furthermore, FIG. 5 shows a fourth embodiment of the present invention, which has a configuration in which the positions of the operational amplifier 2 and the DC power source E are switched in the embodiment of FIG. The operation is the same as in Fig. 2.

In the embodiments shown in FIGS. 2 to 5, an operational amplifier 2 is used as an amplifier for detecting the photoelectric conversion signal.
However, any amplifier for detecting the photoelectric conversion signal may be used as long as the input terminal potential is always kept at the ground potential (or a constant potential). FIG. 6 shows an example of this, which is a common base amplifier consisting of a transistor 3, a load resistor R _L , a diode 4 for setting the operating bias of the transistor 3, and a resistor 5.
Input terminal 6 is always kept at ground potential. Therefore, by replacing the operational amplifier 2 in the embodiments shown in FIGS. 2 to 5 with the amplifier shown in FIG. 6, exactly the same photoelectric conversion operation can be achieved.

As explained above, the present invention is configured to scan by driving a photoconductive element array in a matrix, and a direct current is applied to either the selection switch array on the common electrode side of the matrix or the selection switch array on the individual electrode side. In addition to connecting the power supply, the other selection switch rows are connected to a signal amplifier that has the function of keeping the input terminal voltage always at ground potential (or a constant potential), and the input terminal of this amplifier is connected to the selected optical The present invention provides a photoelectric conversion device in which only current flows through a conductive element.

Since the photoelectric conversion device according to the present invention has the configuration described above, it does not require a blocking diode to prevent reverse current, and since the blocking diode is not required, the photoconductive element array It is easy to increase the density and can be realized at low cost with a simple configuration. Furthermore, there is an advantage that the output signal level can be increased compared to conventional photoelectric conversion devices.
Further, since one of the switches on the common electrode side or the individual electrode side can be an open/close switch with a small number of rotating elements, there is an effect that the number of rotating elements can be reduced.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a conventional photoelectric conversion device.
2 to 5 are block diagrams showing an embodiment based on the present invention, and FIG. 6 shows the same photoelectric conversion operation by replacing the signal detection amplifier part in the photoelectric conversion device of FIGS. 2 to 5. FIG. 2 is a configuration diagram of a signal detection amplifier that can perform In the figure, 1...Signal output terminal, 2...Operation amplifier, 3...Transistor, 4...Diode, 5...Resistor, 6...Signal input terminal, _SX1 , _SX2 ... _SXn ...Common electrode side selection switch row, SY ₁ , _SY2 ... _SY5 ...
Individual electrode side selection switch row, R ₁ , R ₂ ... R _o ... photoconductive element row, R _L ... load resistance, E ... DC power supply. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a device configured to drive a photoconductive element array in a matrix, an input terminal on the common electrode side (or individual electrode side) is always kept at a constant potential V including the ground potential. A switch array is arranged to connect to a signal amplifier having means, and the individual electrode side (or common electrode side) is connected to a DC power supply side of a predetermined voltage or a constant potential V side including ground potential. A photoelectric conversion device characterized in that a switch row is arranged. 2. As a signal amplifier that has means to keep the input terminal at a constant potential, a constant potential V (including ground potential) is supplied to the positive input terminal, and a load resistor is connected between the negative input terminal and the output terminal. 2. The photoelectric conversion device according to claim 1, characterized in that an operational amplifier having the following configuration is used. 3 In a device configured to drive a photoconductive element array in a matrix, the common electrode side (or individual electrode side) has a signal amplifier side that has means for keeping the input terminal always at a constant potential V including the ground potential. A row of changeover switches are arranged to switch to the fixed potential V side, which includes the ground potential, or the ground potential, and an open/close switch is arranged on the individual electrode side (or the common electrode side) to connect to a DC power source with a predetermined voltage. Features of photoelectric conversion device.