JPH0691602B2 - Image sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image sensor that sequentially scans a plurality of photodiodes based on a sawtooth voltage.

[Prior Art] An image sensor has a plurality of photodiodes for converting optical information into electric signals and an analog switch for electrically scanning the plurality of photodiodes to selectively obtain electric signals. is doing. The analog switch is composed of a field effect transistor (FET) as disclosed in JP-A-63-2377, for example, and is arranged in the vicinity of a plurality of photoelectric conversion elements.

By the way, in the image sensor of the integrated circuit, the width of one photodiode, that is, one pixel (for example, 125 μ
One field effect transistor must be arranged to fit in m). However, it is not easy to form a field effect transistor so as to fit in such an extremely narrow width. Further, when the three wiring conductor layers for the drain, the source and the gate of the field effect transistor are provided within a predetermined width on the substrate, the width of the three wiring conductor layers is inevitably narrowed. Yield of manufacturing was low.

In order to solve this type of problem, a method of scanning a photodiode using a series circuit of diodes is disclosed in Japanese Patent Application No. 1-198279.

[Problems to be Solved by the Invention] FIG. 12 shows one of the image sensors disclosed in the above application.
An equivalent circuit of a bit (unit circuit) is shown. This image sensor includes a first diode Da1 connected to the sawtooth voltage source 1, a series circuit of a first resistor Ra1 and a second diode Db1 connected in parallel to the voltage source 1, and It has a second resistor Rb1 connected in parallel to the series circuit, and a series circuit consisting of a photodiode S1 and a blocking diode Dc1 connected substantially in parallel to the second diode Db1.

In the circuit of FIG. 12, if the common line L connecting the second diode Db1 to the ground terminal of the voltage source 1 is accidentally opened at the position indicated by the mark due to connection failure or disconnection, the second diode Db1 In contrast, the photodiode S
Since 1 is no longer connected in parallel, it becomes impossible to limit the voltage of the photodiode S1 to the forward voltage of the second diode Db1. As a result, the maximum voltage of the sawtooth wave voltage source 1 is applied to the photo die auto S1, which may be destroyed.

Then, the objective of this invention is providing the image sensor which can prevent the above-mentioned destruction of a photodiode.

[Means for Solving the Problems] The present invention for achieving the above object will be described with reference to the reference numerals of the drawings showing an embodiment. A sawtooth wave that increases or decreases continuously or stepwise with time is supplied. Is a circuit in which a plurality of first diodes Da1 to Da3 each having a first electrode and a second electrode are connected in series, and one end of which is connected to the voltage source 1. And each of the first diodes Da1 to Da3 has a directivity such that a forward current of each of the first diodes Da1 to Da3 flows based on the sawtooth wave, and each of the first diodes Da1 to Da3 has a directivity. ~ Da3 of the first series circuit in which the first electrodes are arranged on the side of the voltage source 1 and the first impedance elements Ra1 to Ra3 or Ca1 to Ca3 and the second series circuit, respectively.
Each of the diodes Db1 to Db3 is connected in series, and is connected between the second electrodes of the first diodes Da1 to Da3 and the other end of the voltage source 1, respectively.
And a plurality of second series circuits in which the respective second diodes Db1 to Db3 have directivities such that the forward currents of the respective second diodes Db1 to Db3 flow based on the sawtooth wave, Each first diode Da1 to Da3
A plurality of second impedance elements Rb1 to Rb3 respectively connected between the second electrode and the other end of the voltage source 1.
Alternatively, C1 to C3 and the first impedance element Ra1 to Ra3
Alternatively, a plurality of photodiodes S1 to S3, which are respectively connected between connection points P1 to P3 of Ca1 to Ca3 and the second diodes Db1 to Db3 and a common current output line 3, and the plurality of photodiodes S1 to S3. In order to prevent mutual interference of the photodiodes S1 to S3, the plurality of blocking diodes Dc1 to Dc3 having the opposite directivity to the photodiodes S1 to S3 and connected to the passage through which the current of the photodiodes S1 to S3 flows. And a common current-voltage conversion circuit 2 connected between the common current output line 3 and the other end of the voltage source 1, the common current output line 3 or the voltage source A photodiode protection impedance element 6 is connected between the other end of the second diode Db1 to Db3 and a terminal of the second diode Db1 to Db3 not connected to the first impedance element Ra1 to Ra3 or Ca1 to Ca3. The It is those related to the image sensor.

The photodiode protection impedance element (6) has an impedance value larger than the input impedance of the current-voltage conversion circuit 2, and has the plurality of first and second impedance elements Ra1 to Ra3 or Ca1 to C.
It is desirable to have an impedance value smaller than the parallel combined impedance value of a3, Rb1 to Rb3 or C1 to C3.
Further, it is desirable to connect the bias voltage source 7 to the second diodes Db1 to Db3.

[Operation] The photodiode protection impedance element 6 according to the present invention is connected in parallel to the photodiodes S1 to S3 when the problem described in FIG. 12 occurs. This allows
First and second impedance elements Ra1 to Ra3 or Ca1 to C
A3, Rb1 to Rb3 or Cb1 to Cb3 and the impedance Z of the photodiode protection impedance element 6 are applied to the photodiodes S1 to S3 divided by the voltage dividing circuit. Therefore, the applied voltage to the photodiodes S1 to S3 can be suppressed.

Further, by setting as set forth in claim 2, it becomes possible to sufficiently reduce the voltages of the photodiodes S1 to S3 at the time of abnormality, and it becomes possible to effectively convert the output current into a voltage.

[Embodiment] The one-dimensional image sensor according to the embodiment of the present invention shown in FIG. 1 includes a voltage source 1, three unit circuits K1, K2, K3 corresponding to three pixels or bits, and a current- The voltage conversion circuit 2 is included. This one-dimensional image sensor is configured to be able to detect a number of pixels greater than three. However, since it is difficult to show the entire structure of this one-dimensional image sensor in the drawing, only a part thereof is shown in FIG.

The three unit circuits K1, K2, K3 that are the same as each other include a first diode Da1, Da2, Da3 and a second diode Db1, Db2, D3.
b3, the first resistors Ra1, Ra2, Ra3, and the second resistors Rb1, Rb
2, Rb3, and photodiodes S1, S2, S3 for light detection,
It consists of blocking diodes Dc1, Dc2 and Dc3.

One end (left end) of a circuit (first series circuit) in which three first diodes Da1, Da2, Da3 each having an anode (first electrode) and a cathode (second electrode) are connected in series is It is connected to one end of the voltage source 1. The first diodes Da1, Da2, Da3 have a directivity that is forward biased by the voltage of the voltage source 1. That is, the anodes (first electrodes) of the first diodes Da1 to Da3 are arranged on the voltage source 1 side. When the upper terminal of the voltage source 1 is negative, the cathodes of the first diodes Da1 to Da3 are arranged on the voltage source 1 side.

Between the cathodes (second electrodes) of the first diodes Da1, Da2, Da3 and the other end (ground) of the voltage source 1, the first resistors Ra1, Ra2, Ra3 as first impedance elements and Circuits (second series circuits) in which the two diodes Db1, Db2, Db3 are connected in series are respectively connected. The second diodes Db1, Db2, Db3 have a directionality in which they are forward biased by the voltage of the voltage source 1.
Second resistors Rb1 to Rb3 as second impedance elements
Are connected between the cathodes of the first diodes Da1 to Da3 and the ground. The second diodes Db1 to Db3
The cathode and the lower ends of the second resistors Rb1 to Rb3 are connected to the ground terminal of the voltage source 1 by the common line L.

First resistors Ra1, Ra2, Ra in each unit circuit K1, K2, K3
Interconnection point P1, P3 of the third diode Db1, Db2, Db3
2, P3 is connected to one end of a series circuit (third series circuit) of the photodiodes S1, S2, S3 and the blocking diodes Dc1, Dc2, Dc3, that is, the cathodes of the photodiodes S1 to S3. The anodes of the photodiodes S1 to S3 are connected to the common current output line 3 via blocking diodes Dc1, Dc2 and Dc3 for preventing mutual interference of the photodiodes S1 to S3.

The current-voltage conversion circuit 2 comprises an operational amplifier 4 and a feedback resistor Rf. The inverting input terminal of the operational amplifier 4 is connected to the common current output line 3, the non-inverting input terminal is connected to the other end (ground) of the voltage source 1, and the feedback resistor Rf is provided between the inverting input terminal and the output terminal. It is connected. The output terminal of the operational amplifier 4 is connected to the output terminal 5 via the inverting amplifier 4a. The photodiodes S1 to S3 are the second diodes.
Substantially in parallel with Db1 to Db3. The photodiodes S1 to S3 are connected so as to be reverse biased by the voltage of the voltage source 1.

The photodiode protection impedance element 6 according to the present invention is connected between the common current output line 3 and the cathode common line L of the second diodes Db1 to Db3. The impedance Z of the impedance element 6 composed of a resistor is 10
kΩ, which is larger than the input impedance Z1 of the current-voltage conversion circuit 2. The impedance Z is smaller than the parallel combined impedance Z2 of the first resistors Ra1 to Ra3 and the second resistors Rb1 to Rb3.

Details of each part of the image sensor of FIG. 1 are as follows.

The voltage source 1 is composed of a circuit that generates a sawtooth wave, and periodically generates a sawtooth wave, that is, a sweep signal shown in FIG. The maximum amplitude value of the sawtooth wave in FIG. 2 is set to a value capable of turning on all the first and second diodes Da1 to Da3 and Db1 to Db3 in FIG.

Photodiodes S1 to S3, first diodes Da1 to Da3,
Second diodes Db1 to Db3, blocking diode Dc
1 to Dc3 are each a PIN junction diode, which is a hydrogenated amorphous silicon semiconductor layer, one electrode layer provided below the semiconductor layer, and the other electrode layer provided above the semiconductor layer. And are provided on a common insulating substrate (not shown).

Since the photodiodes S1 to S3 are reverse biased,
It is equivalently shown by the parallel circuit of the capacitance Cs and the current source Is proportional to the light intensity shown in FIG. The value of the current flowing through the equivalent capacitance Cs of the photodiodes S1 to S3 is extremely small.

The first diodes Da1 to Da3 and the second diodes Db1 to D
The voltage across both ends when b3 is turned on, that is, the forward voltage Vf is approximately 0.8V. The first resistors Ra1 to Ra3 are 90kΩ each
And the second resistors Rb1 to Rb3 are each 90 kΩ,
These are formed of a material such as TiO ₂ , Ta-SiO ₂ or NiCr.

According to the image sensor of the present embodiment using the diode as the switch element, the width of the wiring conductor can be set to 20 μm or more in the image sensor having the bit interval of 125 μm, and the manufacturing yield is greatly improved. In the case of the conventional image sensor in which the switch element is composed of the field effect transistor, it is necessary to set the width of the wiring conductor to about 10 μm.

[Operation] In the image sensor of FIG. 1, when the sawtooth wave shown in FIG. 2 is generated from the voltage source 1, the first diode Da1 is generated.
~ Da3 becomes conductive one after another. First, when the ramp voltage of the sawtooth wave gradually increases, the first diode Da1 of the unit circuit K1 is turned on. While the first diode Da1 of the unit circuit K1 is non-conducting (OFF state), the cathode of the first diode Da1 is almost zero volt, but the first diode Da1 is turned on and the voltage source is further increased. When the voltage Vd of 1 becomes higher, the cathode voltage Vd of the first diode Da1 becomes higher following the voltage Vd. That is, when the first diode Da1 is turned on, the voltage across this is almost fixed to the forward voltage Vf, so the voltage obtained by subtracting the forward voltage Vf of the diode Da1 from the power supply voltage Vd is the second resistance Rb1.
Join both ends of. Also, the second diode of the unit circuit K1
During the period when Db1 is non-conducting, the potential at the point P1 is approximately equal to the voltage across the second resistor Rb1. Therefore, the first diode Da1
After being turned on, the potential Vp1 at the point P1 gradually rises as shown in FIG. 4 (A). When the potential Vp1 at the point P1 becomes the forward voltage Vf of the second diode Db1, this turns on, and the potential Vp1 at the point P1 becomes a substantially constant value (Vf). Almost at the same time when the second diode Db1 of the unit circuit K1 is turned on, the first diode Da2 of the unit circuit K2 is turned on.
And the potential Vp2 is obtained at the point P2 as shown in FIG. 4 (A). When the ramp voltage of the sawtooth wave supplied from the voltage source 1 further increases, the first
The diode Da3 of is turned on and the potential Vp3 of FIG. 4 (A) is obtained at the point P3. Potentials at points P1 to P3 Vp1 to Vp3
When P changes sequentially as shown in FIG. 4 (A), each point P1
The photodiodes S1 to S3, which are connected via the current-voltage conversion circuit 2 between .about.P3 and the ground, are sequentially driven. That is, the photodiodes S1 to S3 are electrically scanned.

In the circuit of FIG. 1, the photodiodes S1 to S3 are arranged one-dimensionally. When reading optical information with the photodiodes S1 to S3, first, the first diodes Da1 to D1 are read.
The voltage source 1 generates a voltage capable of turning on a3 and all of the second diodes Db1 to Db3. In addition,
First diodes Db1 to Db3 and second diodes Db1 to D
The voltage for turning on all of b3 can be given by a sawtooth wave shown in FIG. That is, the maximum value of the sawtooth wave and the voltage value in the vicinity thereof can turn on all the first and second diodes Da1 to Da3 and Db1 to Db3.

First diodes Da1 to Da3 and second diodes Db1 to Db
While all of b3 are in the ON state, the photodiodes S1 to S3 are reverse-biased by the forward voltage Vf of the second diodes Db1 to Db3 obtained at the points P1 to P3, which is equivalent to FIG. The indicated capacitance Cs is charged. Since the equivalent capacitance Cs is extremely small, the charging of the equivalent capacitance Cs can be achieved by the minute current in the region before the point where the forward currents of the blocking diodes Dc1 to Dc3 rise sharply.

When an optical signal obtained from an object (not shown) such as a facsimile document arranged opposite to the image sensor of FIG. 1 is input to the photodiodes S1 to S3,
Photodiode S1 ~
The charge amount of the equivalent capacitance Cs of S3 changes. That is, among the photodiodes S1 to S3, the equivalent capacitance Cs is discharged in the one where the optical signal is input, and the equivalent capacitance Cs is not discharged in the one where the optical signal is not input. The amount of discharge of the equivalent capacitance Cs changes depending on the amount of light. There are two methods of giving an optical input to the photodiodes S1 to S3. One of them is a method of always giving a light input to the photodiodes S1 to S3, and the other is a method of giving a light input only for a predetermined period (for example, a period when the voltage Vd of the voltage source 1 is zero volt). is there.

When the voltage Vd of the voltage source 1 linearly increases with time as shown in FIG. 2, potentials Vp1, Vp2, Vp3 are obtained at points P1 to P3 as shown in FIG. The photodiodes S1 to S3 are sequentially reverse biased. In other words, the voltage for charging the equivalent capacitance Cs shown in FIG. 3 is applied to the photodiodes S1 to S3. At this time, the charging current flows to the ones which are discharged by the light input within the equivalent capacitance Cs of the photodiodes S1 to S3, but the charging current does not flow to the ones which are not discharged because there is no light input. . The charging current of the equivalent capacitance Cs of the photodiodes S1 to S3 is the blocking diodes Dc1 to Dc.
Since it flows through c3 and the current-voltage conversion circuit 2, the voltage Vout of the output terminal 5 changes depending on the presence or absence of the charging current.
The potentials Vp1 to Vp3 shown in FIG. 4 (A) are sequentially applied to the photodiodes S1 to S3 while the respective equivalent capacitances Cs are discharged due to the light input to all the three photodiodes S1 to S3. When applied, the voltage Vout at the output terminal 5 is changed to the photodiode S1 as shown in FIG. 4 (B).
~ It changes every time charging current flows to S3. That is, each point P1 ~
The equivalent capacitance Cs increases as the potential Vp1 to Vp3 of P3 increases.
When the charging current increases, and the potentials Vp1 to Vp3 at the points P1 to P3 saturate, the charging current decreases and an output voltage Vout corresponding to this change in charging current is obtained.

FIG. 4C shows three photodiodes S1, S2, S3.
The change of the voltage Vout of the output terminal 5 is shown when the light input is not given to S2 and the light input is given only to S1 and S3. In this case, the potentials Vp1 to Vp3 shown in FIG.
Is sequentially applied to the photodiodes S1 to S3, no charging current flows in the photodiode S2. That is, the fourth
The output voltage Vout corresponding to the potential Vp2 shown in FIG. The current Iout of the common current output line 3 is the current −
It flows through the feedback resistor Rf of the voltage conversion circuit 2. Therefore, the output voltage Vout obtained by multiplying Iout by Rf is generated.

By the way, in the image sensor of FIG. 1, a connection failure (open state) to the ground terminal of the voltage source 1 of the cathode common line L of the second diodes Db1 to Db3 has occurred, and the ground of the non-inverting input terminal of the operational amplifier 4 has occurred. If the disconnection (open state) to erroneously occurs, the equivalent circuit shown in FIG. 5 is established. Although only one unit circuit is shown in FIG. 5, another unit circuit is in the same state. Even if the run L is open, the voltage source 1, the first diode Da1, the first resistor Ra1, the second diode Db
1. Since the closed circuit composed of the impedance element 6 is formed, the second diode Db1 can be turned on. When the second diode Db1 is in the ON state, the impedance element Z is connected in parallel to the series circuit of the photodiode S1 and the blocking diode Dc1 via the extremely small resistance of the second diode Db1. Now, in FIG. 5, the resistances of the first and second diodes Da1 and Db1 are ignored, and the first and second resistances Ra1 to Ra3 and Rb1 to Rb3.
If the total parallel combined impedance of the above is Z2, a voltage of VdZ / (Z + Z2) is applied to the high impedance series circuit composed of the photodiode S1 and the blocking diode Dc1. That is, a voltage obtained by dividing the power supply voltage Vd is applied to the series circuit of the photodiode S1 and the blocking diode Dc1. Thereby, the photodiode S1 can be protected from overvoltage.

The smaller the value Z of the impedance element 6 made of a resistor, the higher the effect of suppressing the abnormal high voltage of the photodiodes S1 to S3. However, since a part of the signal current Iout of the common current output line 3 flows into the impedance element 6, the sensitivity of the current-voltage conversion circuit 2 is reduced. Therefore, it is desirable to make the value Z of the impedance element 6 larger than the input impedance Z1 of the current-voltage conversion circuit 2.

[Modification] The present invention is not limited to the above-described embodiments, and the following modifications are possible, for example.

(1) The blocking diodes Dc1 to Dc3 for preventing the mutual interference of the photodiodes S1 to S3 are connected to the first resistors Ra1 to R.
It can be connected in series with a3, or between the second resistors Rb1 to Rb3 and the first resistors Ra1 to Ra3.

(2) When the image sensor shown in FIG. 1 is used for a facsimile, a unit corresponding to the unit circuits K1 to K3 is used, for example.
It is necessary to provide 2000 pieces. First diode Da1
.About.Da3 and the maximum value of the sawtooth wave for simultaneously turning on a large number of diodes corresponding to the second diodes Db1 to Db3 becomes extremely high. 6 and 7 show the voltage source 1
One method by which the maximum voltage of the can be kept low is shown. In FIG. 6, n unit circuits corresponding to the unit circuits K1 to K3 in FIG. 1 are divided into m circuit blocks B1, B2 ... Bm. Each of the circuit blocks B1 to Bm includes several to several tens of units corresponding to the unit circuits K1 to K3 in FIG. 1, and corresponds to a circuit in which the voltage source 1 is omitted from the image sensor in FIG. is there. Each circuit block B1 to Bm is connected to the voltage source 1a via the multiplexer 10. Each circuit block B1
Output terminals of ~ Bm are commonly connected via amplifiers A1 ~ Am. The voltage source 1a repeatedly generates a sawtooth wave (triangular wave) shown in FIG. 7 (A). The multiplexer 10 is the 7th
As shown in FIGS. 7B and 7C, the sawtooth wave shown in FIG. 7A is distributed to the circuit blocks B1 to Bm. Each circuit block B1
The light input to each photodiode of .about.Bm is always given as shown in FIG. 7 (D).

(3) As shown in FIG. 8, the second resistors Rb1 to Rb3 as the second impedance element in FIG. 1 are replaced with a capacitor C1 which is sufficiently larger than the equivalent capacitance of the photodiodes S1 to S3.
Can be replaced with ~ C3. Further, instead of the capacitors C1 to C3 shown in FIG. 8, a diode may be connected so as to be reverse biased, and this diode may be used as an equivalent capacitance.

(4) As shown in FIG. 9, instead of the first resistors Ra1 to Ra3 as the first impedance element in FIG. 1, a capacitor Ca larger than the equivalent capacitance of the photodiodes S1 to S3 is used.
It can be replaced with 1 to Ca3. Also, the capacitors Ca1 to Ca3 in FIG. 9 can be replaced with reverse biased diodes which function equivalently thereto.

(5) The first resistors Ra1 to Ra3 in FIG. 1 are replaced with a first capacitance element composed of a capacitor or a reverse bias diode, and the second resistors Rb1 to Rb3 are replaced with a second capacitance composed of a capacitor or a reverse bias diode. It can be replaced with an element. In this case, it is desirable that the capacitance value of the second capacitance element be equal to or larger than the capacitance value of the first capacitance element.

(6) The sawtooth wave can be a stepwise sawtooth wave as shown in FIG. 10 and a sawtooth wave increasing quadratically as shown in FIG.

(7) The polarities of the diodes and the voltage source 1 can be reversed.

(8) Although hydrogenated alumophus silicon (amorphous silicon) is used as the diodes Da1 to Da3 and Db1 to Db3 in the embodiments, amorphous silicon carbide or the like may be used.

(9) Diodes Da1 to Da3, Db1 to Db3, Dc1 to Dc3 are PI
It may be any of N, PI, IN, Schottky junction diode and the like.

(10) A voltage may be applied to the cathode terminals of the second diodes Db1 to Db3. That is, as shown in FIG. 13, the ground and the cathode common line L of the second diodes Db1 to Db3.
A bias voltage source 7 may be connected between and. Thereby, the dynamic range can be expanded. In this case, the photodiode protection impedance element 6 is connected between the common line L and the ground. As a result, even if the bias voltage source 7 is disconnected from the common line L, no overvoltage is applied to the photodiodes S1 to S3. The bias voltage source 7 is preferably a circuit that generates a voltage having a slope opposite to that of the sawtooth wave voltage Vd shown in FIG.

(11) The first and second impedance elements are connected to a resistor,
Either one of a capacitor and a diode may be used, or these may be connected in series or in parallel. When the first and / or the second impedance element is a capacitor, since it has frequency dependence, Z2> Z must be satisfied within the range up to the driving frequency.

(12) In Fig. 1, change the value of the second resistor from Rb1 to Rb3.
May be set so as to gradually increase toward [Effect of the invention] As described above, according to the present invention, it is possible to prevent the breakdown of the photodiode due to the overvoltage due to the disconnection or disconnection of the wiring.

[Brief description of drawings]

1 is a circuit diagram showing an image sensor according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing a sawtooth wave, FIG. 3 is an equivalent circuit diagram of a photodiode, and FIG. 4 (A) is FIG. Showing potential changes at points P1 to P3 of the circuit of FIG. 4, and FIG. 4 (B) shows voltage changes of the output terminal of the circuit of FIG.
FIG. 4 (C) is a diagram showing a state where light is input to all of the two photoelectric conversion elements, and FIG.
FIG. 5 is a diagram showing a state where light is input to only two of the photoelectric conversion elements, FIG. 5 is a circuit diagram for explaining protection of the photodiode in the event of an abnormality, and FIG. 6 has a large number of unit circuits. FIG. 7 is a block diagram showing in principle the driving method of the photodiode at this time, FIG. 7 is a diagram showing the state of each part of FIG. 6, and FIGS. 8 and 9 are circuit diagrams showing a modified image sensor. 11 and 12 are waveform diagrams showing a modified example of a sawtooth wave, FIG. 12 is a circuit diagram showing an abnormal state of a conventional image sensor, and FIG. 13 is a circuit diagram showing an image sensor of another modified example. 1 ... Voltage source, Da1-Da3 ... Diode, Ra1-Ra3 ...
1st resistance, Rb1-Rb3 ... 2nd resistance, S1-S3 ... Photodiode, 2 ... Current-voltage conversion circuit, 6 ... Impedance element.

Claims (2)

[Claims] 1. A plurality of first electrodes each having a voltage source (1) for supplying a sawtooth wave which continuously or stepwise increases or decreases with time, and a first electrode and a second electrode. It is a circuit in which diodes (Da1 to Da3) are connected in series, one end of which is connected to the voltage source (1), and the forward current of each first diode (Da1 to Da3) changes to the sawtooth wave. The respective first diodes (Da1 to Da3) have a directivity such that the first electrodes of the respective first diodes (Da1 to Da3) are on the side of the voltage source (1). And the first series circuit arranged in each of the first impedance circuits (Ra1 to Ra3 or Ca
1 to Ca3) and a second diode (Db1 to Db3) connected in series, each first diode (Da
1 to Da3) respectively connected between the second electrode and the other end of the voltage source (1), and the forward current of each second diode (Db1 to Db3) is based on the sawtooth wave. A plurality of second series circuits in which the respective second diodes (Db1 to Db3) have such a directivity that they flow, and the second electrodes of the respective first diodes (Da1 to Da3). A plurality of second impedance elements (Rb1 to Rb3 or C1) respectively connected to the other end of the voltage source (1).
To C3) and the first impedance element (Ra1 to Ra3 or Ca1 to Ca).
3) and the second diodes (Db1 to Db3), respectively, and a plurality of photodiodes (S1 to S) connected between the respective connection points (P1 to P3) and the common current output line (3).
3) and the current of the photodiodes (S1 to S3) flows in a direction opposite to that of the photodiodes (S1 to S3) to prevent mutual interference of the plurality of photodiodes (S1 to S3). A plurality of blocking diodes (Dc1 to Dc3) connected to the passage, and a common current-voltage conversion circuit connected between the common current output line (3) and the other end of the voltage source (1). (2) An image sensor comprising: a common current output line (3) or the other end of the voltage source (1), and the first impedance element (Ra1 ...) Of the second diode (Db1-Db3). An image sensor characterized in that an impedance element (6) for protecting a photodiode is connected to a terminal on the side not connected to Ra3 or Ca1 to Ca3). 2. The photodiode protection impedance element (6) has an impedance value larger than the input impedance of the current-voltage conversion circuit (2),
The image sensor according to claim 1, wherein the image sensor has an impedance value smaller than a parallel combined impedance value of the plurality of first and second impedance elements.