JPH03285450A - Image sensor - Google Patents

Abstract

PURPOSE:To prevent a photodiode from being destroyed by parallelly connecting an impedance for photodiode protection to the photodiode when any problem is generated. CONSTITUTION:When the defect of connection is generated to the ground terminal of a voltage source 1 in a cathode common line L for second diodes Db1-Db3 and non-connection is erroneously generated to the ground of the noninverted terminal of an operational amplifier 4, an imedance element Z is parallelly connected through the extremely small resistance of the second diode Db1 to a serial circuit composed of a photodiode S1 and a blocking diode Dc1. Thus, the photodiode S1 can be protected against an excess voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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 includes a plurality of photodiodes for converting optical information into electrical signals, and an analog switch for electrically scanning the plurality of photodiodes to selectively obtain electrical signals. are doing.

The analog switch is, for example, a field effect transistor (FE) as disclosed in Japanese Patent Laid-Open No. 63-2377.
T) and is arranged near a plurality of photoelectric conversion elements.

By the way, in an integrated circuit image sensor, the width of one photodiode, that is, one pixel (for example, 125
One field effect transistor must be placed to fit within .mu.m).

However, it is not easy to form a field effect transistor within such an extremely narrow width. Furthermore, when three wiring conductor layers for the drain, source, and gate of a field effect transistor are provided within a predetermined width on the substrate, the width of the three wiring conductor layers inevitably becomes narrower, and the image sensor The manufacturing yield has become low.

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

[Problems to be Solved by the Invention] FIG. 12 shows an equivalent circuit of one bit (unit circuit) of the image sensor disclosed in the above application.

This image sensor includes a first diode Dal connected to a sawtooth voltage source 1, a first resistor Rat and a second diode Dbl connected in parallel to the voltage source 1.
and a second circuit connected in parallel to this series circuit.
, and a series circuit consisting of a photodiode SI and a blocking diode Dc1 connected substantially in parallel to the second diode Dbl.

In the circuit shown in Fig. 12, if the common line L connecting the second diode Db1 to the ground terminal of the voltage source 1 accidentally enters the oven state due to a poor connection or disconnection of F or IJ at the position indicated by the X mark, the second diode The photodiode S] is no longer connected in parallel to the diode Dbl, and it becomes impossible to limit the voltage of the photodiode s1 to the forward voltage of the second diode DblO. As a result, the maximum voltage of the sawtooth voltage source 1 is applied to the photodiode SL, which may be destroyed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image sensor that can prevent the above-mentioned destruction of the photodiode.

[Means for Solving Problem R] To achieve the above object, the present invention will be described with reference to the reference numerals in the drawings showing the embodiments. It is a circuit in which a voltage source 1 for supplying a voltage and a plurality of first diodes Da1 to Da3 each having a first electrode and a second electrode are connected in series, one end of which is connected to the voltage source 1. each of the first diodes Da1 to Da3 has a directionality such that the forward current of each of the first diodes Da1 to Da3 flows based on the sawtooth wave; The first electrodes Da1 to Da3 are arranged on the voltage source 1 side.
series circuits, each with a first impedance element R
a1 to Ra8 or Ca1 to Ca3 and the second diode D
b1 to Db3 connected in series, each connected between the second electrode of each of the first diodes Da1 to Da3 and the other end of the voltage source 1, and each of the second a plurality of second series circuits in which each of the second diodes Db1 to Db3 has a directionality such that the forward current of the diodes Db1 to Db3 flows based on the sawtooth wave; and each of the first diodes a plurality of second impedance elements Rb1-Rbl or C1-C5 respectively connected between the second electrode of D al -Da3 and the other end of the voltage source 1;
Impedance element Ral ~ RC3 or Cal −
A plurality of photodiodes 5L-5 each connected between the connection points P1 to P3 between CC8 and the second diodes Db1 to Db3 and the common current output line 3.
3, and a plurality of photodiodes 5l-33 connected to the path through which the current flows through the photodiodes 81-S3 and having a directionality opposite to that of the photodiodes 5l-33 in order to prevent mutual interference between the plurality of photodiodes 81-S3. blocking diode Del-Dc3 and the common current output line 3
and the other end of the voltage source 1 -
In an image sensor comprising a voltage conversion circuit 2, the common current output line 3 or the other end of the voltage source 1 and the first impedance element Ral-RC3 or Ca1-Ca3 of the second diodes Db1-Db3 are connected to each other. This relates to an image sensor in which a photodiode protection impedance element 6 is connected between the terminal on the unconnected side.

In addition, an impedance element (6
) has an impedance value larger than the input impedance of the current-voltage conversion circuit 2, and the plurality of first
and second impedance elements Ra1 to Ra3 or Ca
It is desirable to have an impedance value smaller than the parallel composite impedance value of l to CC3, Rb1 to Rb3, or C1 to C3. Moreover, the second diode Db1~
It is desirable to connect the bias voltage source 7 to Db3.

[Function] The photodiode protection impedance element 6 according to the present invention is connected in parallel to the photodiodes 51 to S3 when a problem as explained in FIG. 12 occurs. Thereby, the first and second impedance elements Ral ~R
C3 or Ca1 to Ca3, Rb1 to Rb3 or Cbl-
The voltage is applied to the photodiodes 81 to S3 divided by a voltage dividing circuit consisting of the composite impedance value of Cb3 and the impedance Z of the photodiode protection impedance element 6. Therefore, the photodiodes 51~
The voltage applied to S3 can be suppressed.

Further, by setting as shown in claim 2, it becomes possible to sufficiently reduce the voltage of the photodiode 5L-S3 during an 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. It has a conversion circuit 2. This -dimensional image sensor is configured to be able to detect more than three pixels.

However, since it is difficult to show the entire configuration of this one-dimensional image sensor in the drawing, only a part of it is shown in FIG.

Three mutually identical unit circuits Kl, K2, K3 have first diodes Dal, Da2, Da3, second diodes Dbl, Db2, Db3, and a first resistor Ra.
1, Ra2, Ra3 and second resistor RbL Rb2, R
b3 and photodiodes S1, S2, S3 for light detection
and blocking diodes Del, Dc2, and Dc3.

Three first diodes DaL, Da2, Da8 having an anode (first electrode) and a cathode (second electrode)
One end (left end) of a circuit in which these are connected in series with each other (first series circuit) is connected to one end of a voltage source 1. The first diodes Dal, Da2, and Da3 have directionality that is biased in the forward direction by the voltage of the voltage source 1. That is, the anodes (first
electrodes) are arranged on the voltage source 1 side. Note that 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.

′! A first resistor Ra serving as a first impedance element is connected between the cathodes (second electrodes) of the diodes Dal, Da2, and Da3 of s1 and the other end (ground) of the voltage source 1.
t, Ra2, Ra3 and the second diode Dbl, Db2
, Db3 are connected in series (second series circuit). second diode D
bl, Db2, and Db3 have the directionality of being biased in the forward direction 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. Note that the second diodes Db1 to D
The cathode of b3 and the lower ends of the second resistors Rh1 to Rb3 are connected to the ground terminal of the voltage source 1 by a common line L.

The first resistor R in each unit circuit Kl, K2, K3
at, Ra2, Ra3 and second diodes Dbl, D
b2, Db8 interconnection points PL, P2, P3 with photodiodes S1% S2, S3 and blocking diode D
Series circuit with el, Dc2, and Dc8 (third series circuit)
, that is, the cathodes of the photodiodes S1 to S3 are connected. The anodes of the photodiodes 81 to S3 are connected to the common current output line 3 via blocking diodes DclSDe2 and Dc3 for preventing mutual interference of the photodiodes 81 to S3.

The current-voltage conversion circuit 2 includes an operational amplifier 4 and a feedback resistor Rf.
It consists of The inverting input terminal of the operational amplifier 4 is connected to the common current output line 3, and the non-inverting input terminal is connected to the other end of the voltage source 1 (
(ground), and the feedback resistor Rf is connected between the inverting input terminal and the output terminal. The output terminal of the operational amplifier 4 is connected to the output terminal 5 via an inverting amplifier 4a.

Note that the photodiode 5L-33 is substantially connected in parallel to the second diodes Db1 to Db3.

Further, the photodiode 5i-sa is connected so as to be reverse biased by the voltage of the voltage source 1.

A 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 Db8.

Impedance Z of impedance element 6 consisting of a resistor
is 10Ω, which is larger than the input impedance Z1 of the current-voltage conversion circuit 2. Moreover, this impedance Z is the first resistor Ra1 to Ra3 and the second resistor Rb1.
It is smaller than the parallel composite impedance Z2 with ~Rb3.

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

Voltage source 1 consists of a sawtooth wave generating circuit, which periodically generates the sawtooth wave or sweep signal shown in FIG. The maximum amplitude value of the sawtooth wave in FIG. 2 is set to a value that can turn on all the first and second diodes Da1 to Da3 and Db1 to Db3 in FIG. 1.

Photodiodes 81 to S3, first diode Da1
~Da3, the second diode Dbl-Db3, and the blocking diodes Dcl~Dc3 are each PTN
A junction diode consisting of a hydrogenated amorphous silicon semiconductor layer, one electrode layer provided below this semiconductor layer, and the other electrode layer provided above the semiconductor layer, with a common insulation layer. It is provided on a substrate (not shown).

Since the photodiode 5L-53 is reverse biased, it is equivalently represented by a parallel circuit of a capacitance Cs and a current source Is proportional to the light intensity shown in FIG. In addition,
Equivalent capacitance Cs of photodiodes 81 to S8
The value of the current flowing through is extremely small.

When the first diodes Da1 to Da3 and the second diodes Db1 to Db3 are turned on, the voltage across them, ie, the forward voltage Vf, is approximately 0°8V. First resistance Ra1
~Ra3 are each 90Ω, and the second resistor Rb1
-Rb3 are each 90Ω, these are TiO
2. It is made of a material such as Ta-5iO□ or NiC.

According to the image sensor of this embodiment using a diode as a switching element, it is possible to make the width of the wiring conductor 20 μm or more in an image sensor with a bit interval of 125 μm, and the manufacturing yield is significantly improved. Note that in the case of a conventional image sensor in which the switch element is composed of a field effect transistor, the width of the wiring conductor is approximately 10 μm.
It was necessary to make it m.

[Operation] In the image sensor shown in FIG. 1, when the sawtooth wave shown in FIG. 2 is generated from the voltage source 1, the first diode Da
1 to Da3 become conductive in sequence.

First, when the sawtooth wave ramp voltage gradually increases, the first diode Dal of the unit circuit KL turns on. The first diode Da1 of the unit circuit Kl is non-conductive (
OFF state), the cathode of the first diode Dal is at approximately zero volts, while the cathode of the first diode Dal
When the voltage source 1 becomes on and the voltage Vd of the voltage source 1 further increases, the cathode voltage Vd of the first diode Dal follows the voltage Vd and increases. That is, the first diode D
When al turns on, the voltage across it becomes the forward voltage V
Since the voltage is approximately fixed at f, a voltage obtained by subtracting the forward voltage Vf of the diode Dal from the power supply voltage Vd is applied to both ends of the second resistor Rbl. Further, during a period in which the second diode Dbl in the unit circuit is non-conductive, the potential at the point Pl is approximately equal to the voltage across the second resistor Rbl. Therefore, the first
After the diode Dal turns on, the potential Vpl at point P1 gradually rises as shown in FIG. 4(A). When the potential Vpl at the point PI reaches the forward voltage Vf of the second diode DbJ, this turns on, and the potential Vpl at the point PI becomes a substantially constant value (Vf). Unit circuit Kl
Almost at the same time as the second diode Dbl is turned on, the first diode Da2 of the unit circuit 2 is turned on, and the potential Vp is applied to the point P2 as shown in FIG. 4(A).
2 is obtained. When the sawtooth wave ramp voltage supplied from the voltage source 1 further increases, the first diode Da3 of 3 in the unit circuit turns on, and the voltage shown in FIG.
A) potential Vp3 is obtained. Potential Vp of points P1 to P3
When l~vpa changes sequentially as shown in FIG. 4(A), photodiodes 51~S3 connected between each point P1~P3 and the ground via the current-voltage conversion circuit 2
are driven sequentially. That is, photodiodes 81 to S
3 is electrically scanned.

In the circuit of FIG. 1, photodiodes 51 to S3 are arranged one-dimensionally. This photodiode 81~
When reading optical information in S3, first, the first diodes Da1 to Da3 and the second diodes Db1 to Db3
The voltage source 1 generates a voltage that can turn on all of the devices. Note that the first diodes Da1 to Da3
The voltage for turning on all of the second diodes Db1 to Db3 can be given in the form of a sawtooth wave as shown in FIG. That is, the maximum value of the sawtooth wave and the voltage value in the vicinity thereof are the voltage values of the first and second diodes Da1 to Da3.
and all of Db1 to Db3 can be turned on.

During the period when all of the first diodes Da1 to Da3 and the second diodes Db1 to Db3 are in the on state, the point P
Each photodiode 5L-53 is
is reverse biased, and a capacitance Cs, equivalently shown in FIG. 3, is charged. Note that since the equivalent capacitance Cs is extremely small, the blocking diode Del-D
Charging of the equivalent capacitance Cs can be achieved by a minute current in the region below the point where the forward current of c3 rises steeply.

When an optical signal obtained from an object (not shown) such as a facsimile document placed opposite to the image sensor in FIG. Correspondingly, the amount of charge in the equivalent capacitance Cs of the photodiodes 81 to S3 changes. That is, among the photodiodes 51 to S3, the equivalent capacitance Cs is discharged in the one to which the optical signal is input, and the equivalent capacitance Cs is not discharged in the one to which the optical signal is not input. equivalent capacitance C
The amount of discharge of s changes depending on the amount of light.

There are two methods for providing optical input to the photodiodes 51 to S3. One of them is photodiode 81~S3
One method is to always provide optical input to the input device, and the other method is to provide optical input only during a predetermined period (for example, a period when the voltage Vd of the voltage source 1 is 0 volts).

When the voltage Vd of the voltage source 1 increases linearly with time as shown in FIG. 2, the voltage Vd in FIG.
: As shown, the potentials vpl, Vp2, and Vp3 are obtained,
As a result, the photodiodes 81 to S3 are sequentially reverse biased. In other words, a voltage that charges the equivalent capacitance Cs shown in FIG. 3 is applied to the photodiodes 81 to S3. At this time, photodiode 5
Among the equivalent capacitances Cs 1 to S3, a charging current flows to those that are discharged due to optical input, but no charging current flows to those that are not discharged due to no optical input.

Equivalent capacitance Cs of photodiodes 81 to S3
Since the charging current flows through the blocking diodes Dcl to Dc3 and the current-voltage conversion circuit 2, the voltage Vout at the output terminal 5 changes depending on the presence or absence of the charging current. In a state where each equivalent capacitance Cs is discharged because optical input is given to all three photodiodes 5l-83, the potential vpi-v shown in FIG. 4(A)
When p3 is sequentially applied to the photodiodes 5L-S3, the voltage Vout at the output terminal 5 changes each time a charging current flows through the photodiodes 5L-58, as shown in FIG. 4(B). That is, the potential Vpl to V at each point Pi-P3
As p3 increases, the charging current of the equivalent capacitance C5 increases, and when the potentials Vp1 to Vp3 at each point P1 to P3 are saturated, the charging current decreases, and an output voltage Vout corresponding to this change in charging current is obtained.

FIG. 4(C) shows three photodiodes Sl.

No optical input is given to 82 of S2 and S3, and St and S
Voltage Vo of output terminal 5 when optical input is given only to terminal 3
The change in ut is shown. In this case, Fig. 4 (A
) The potentials Vpl to Vp3 shown in the photodiodes 81 to
When sequentially applied to S3, no charging current flows through photodiode S2. That is, a change in the output voltage V out corresponding to the potential Vp2 shown in FIG. 4(A) does not occur. The current I out of the common current output line 3 flows through the feedback resistor Rf of the current-voltage conversion circuit 2 . Therefore,
An output voltage v out is generated by multiplying I out by Rf.

By the way, in the image sensor shown in FIG. 1, a connection failure (open state!) of the cathode common line L of the second diodes DbL to Db3 to the ground terminal of the voltage source 1 occurs, and the non-inverting input terminal of the operational amplifier 4 If a disconnection (open state) to the ground occurs by mistake, both of the circuits shown in Fig. 5 will be established.Although only one unit circuit is shown in Fig. 5, other unit circuits may be similarly connected. Even if the line L is open, a closed circuit consisting of the voltage source 1, the first diode Dal, the first resistor Ral, the second diode Dbl, and the impedance element 6 is formed. It is possible to switch the diode Dbl to the on state.When the second diode Dbl is in the on state, the impedance element Z is connected to the photodiode S through the extremely small resistance of the second diode Dbl.
1 and a blocking diode Del in parallel.

Now, in FIG. 5, the first and second diodes D
Ignoring the resistance of ah D bl, the first and second resistances R
If the parallel composite impedance of all a1 to Ra3 and Rb1 to Rb3 is 22, a voltage of VdZ/(Z+22) is applied to the high impedance series circuit consisting of the photodiode Sl and the blocking diode Del. That is, the voltage obtained by dividing the power supply voltage Vd is applied to the photodiode S1 and the blocking diode De.
applied to the series circuit with l.

Thereby, the photodiode SL 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 abnormally high voltage of the photodiodes 5l-3S. However, the signal current 1 o of the common current output line 3
Since a part of ut flows into the impedance element 6, the sensitivity of the current-voltage conversion circuit 2 decreases. 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.

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

(1) Blocking diodes Dcl to Dc8 for preventing mutual interference of the photodiodes 81 to S3 are connected in series to the first resistor Ral-Ra3, or the second resistors Rb1 to Db3 and the first resistor Ra1 are connected in series. ~Ra3.

(2) When the image sensor shown in FIG. 1 is used in a facsimile machine, it is necessary to provide, for example, 2000 unit circuits corresponding to 3 in the unit circuit Kl~. First diodes Da1 to Da3 and second diodes Db1 to Db
The maximum value of the sawtooth wave for turning on a large number of diodes corresponding to 3 at the same time is extremely high. 6 and 7 show one method by which the maximum voltage of the voltage source 1 can be kept low. In Figure 6, 1 is added to the unit circuit in Figure 1.
n unit circuits corresponding to 3 are divided into m circuit blocks Bl, B2 and B-. Each circuit block 81 to Bm includes several to several dozen unit circuits corresponding to 1 to 3 of the unit circuits in FIG. 1, and corresponds to the circuit in which the voltage source 1 is omitted from the image sensor in FIG. It is something.

Each circuit block Bl to Bm is connected to a voltage source 1a via a multiplexer 10. Each circuit block 81~
The output terminals of Bo+ are commonly connected via amplifiers Al to Am. The voltage source 1a repeatedly generates a sawtooth wave (triangular wave) shown in FIG. 7(A). As shown in FIGS. 7(B) and 7(C), the multiplexer 10 is configured as shown in FIG.
The sawtooth wave is distributed to circuit blocks 81 to BIC.

Optical input to each photodiode of each circuit block 81 to Bm is always provided as shown in FIG. 7(D).

(3) As shown in FIG. 8, the second resistors Rb1-Rb3 as the second impedance elements in FIG. 1 are replaced with capacitors C1-C3 that are sufficiently larger than the equivalent capacitance of the photodiodes 81-S3. I can do it. Also,
In place of the capacitors Ct to C3 in FIG. 8, diodes may be connected so as to be reverse biased, and these diodes may be used as equivalent capacitors.

(4) As shown in FIG. 9, the first resistors Ra1 to Ra3 as the first impedance elements in FIG. 1 are replaced with capacitors Cal to Ca3 that are larger than the equivalent capacitance of the photodiodes 5l-53. I can do it. Also, the capacitors Cal to Ca3 in FIG. 9 can be replaced with reverse-biased diodes that function equivalently.

(5) The first resistor Ral-Ra3 in FIG. 1 is replaced with a first capacitive element made of a capacitor or a reverse bias diode, and the second resistors Rb1 to Rb3 are replaced with a second capacitor made of a capacitor or a reverse bias diode. element.

In this case, it is desirable that the capacitance value of the second capacitive element be greater than or equal to the capacitance value of the first capacitive element.

(6) The sawtooth wave can be a stepped sawtooth wave as shown in FIG. 10, or a sawtooth wave that increases in a quadratic curve as shown in FIG.

(7) The polarity of each diode and the polarity of the voltage source 1 can also be reversed.

(8) In the example, diodes Da1 to Da3, Db1
Although hydrogenated amorphous silicon (amorphous silicon) was used as Db3, amorphous silicon carbide or the like may also be used.

(9) Diodes Da1 to Da3, Db1 to Db3
, Dc1 to DC3 may be any of PINS PI, IN, Schottky junction diodes, etc.

(10) A voltage may be applied to the cathode terminals of the 217th diodes Db1 to Db3. That is, as shown in FIG. 13, the ground and the second diodes Db1 to Db3
A bias voltage source 7 may be connected between the cathode common line L and the cathode common line L. This makes it possible to expand the dynamic range. In this case, the photodiode protection impedance element 6 is connected between the common line L and the ground.

Thereby, even if the bias voltage source 7 is disconnected from the common line L, no overvoltage is applied to the photodiodes 81 to S3. It is preferable that the bias voltage source 7 is a circuit that generates a voltage having a slope opposite to that of the sawtooth voltage Vd shown in FIG.

(11) The first and second impedance elements may be configured with any one of a resistor, a capacitor, and a diode, or may be configured by connecting these in series or in parallel. Note that when the first and/or second impedance elements are capacitors, in order to have frequency dependence, 22 > Z must be satisfied in the range up to the drive frequency.

(12) In FIG. 1, the value of the second resistor may be set to gradually increase from Rbl to Rb3 [Effects of the Invention] As described above, according to the present invention, the wiring can be Destruction of the photodiode due to overvoltage caused by disconnection can be prevented.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an image sensor according to an embodiment of the present invention, Figure 2 is a waveform diagram showing a sawtooth wave, Figure 3 is an equivalent circuit diagram of a photodiode, and Figure 4 (A).
is a diagram showing potential changes at each point Pi to P8 of the circuit in Figure 1, and Figure 4 (B) shows voltage changes at the output terminal of the circuit in Figure 1 by 3.
Figure 4 (C) shows a state in which there is optical input to all of the two photoelectric conversion elements.
Figure 5 shows a state in which only two of the photoelectric conversion elements receive optical input, Figure 5 is a circuit diagram to explain photodiode protection in abnormal situations, Figure 6 shows a large number of unit circuits. 7 is a diagram showing the state of each part in FIG. 6, FIGS. 8 and 9 are circuit diagrams showing modified image sensors, and FIG. 11 and 11 are waveform diagrams showing a modified example of the sawtooth wave, FIG. 12 is a circuit diagram showing a conventional image sensor when an abnormality occurs, and FIG. 13 is a circuit diagram showing another modified example of the image sensor. 1... Voltage source, Da1-Da3... Diode, R
a1 to Ra3...first resistance, Rb1 to Rb3...
Second resistor, 81-S3... Photodiode, 2.
...Current-voltage conversion circuit, 6... Impedance element. Agent: Nori Takano 2nd figure, 4th figure, Ichigo - 1st figure, 10th figure, 11th figure, 11th figure, 1+ Il now M, 5th figure, 6th figure, 12th figure, 7th figure (A) vc+ u, lya V (B) 7'low v7F31 l for 1-, → Kude 1
-(C) 7° mouth/nof Bm 5L

Claims (1)

[Claims] [1] A plurality of voltage sources each having a voltage source (1) for supplying a sawtooth wave that increases or decreases continuously or stepwise with time, and a first electrode and a second electrode. A circuit in which first diodes (Da1 to Da3) are connected in series, one end of which is connected to the voltage source (1),
In addition, each of the first diodes (Da1 to Da3) has a directionality such that the forward current of each of the first diodes (Da1 to Da3) flows based on the sawtooth wave.
has, and each first diode (Da1 to D
a3) a first series circuit in which the first electrode is placed on the side of the voltage source (1);
or Ca1 to Ca3) and the second diode (Db1 to D
b3) connected in series, each connected between the second electrode of each first diode (Da1 to Da3) and the other end of the voltage source (1), and a plurality of second series circuits in which each second diode (Db1 to Db3) has a directionality such that the forward current of the second diode (Db1 to Db3) flows based on the sawtooth wave; , a plurality of second impedance elements (Rb1 to Rb1 to
Rb3 or C1 to C3), the first impedance element (Ra1 to Ra3 or Ca1 to Ca3), and the second
A plurality of photodiodes (S1 to S3) are connected between respective connection points (P1 to P3) with the diodes (Db1 to Db3) and a common current output line (3).
) and the photodiodes (S1 to S3) to prevent mutual interference between the plurality of photodiodes (S1 to S3).
3), the photodiode (S1
A plurality of blocking diodes (Dc1 to Dc3) connected to the path through which the current of ~S3) flows, and a plurality of blocking diodes (Dc1 to Dc3) connected between the common current output line (3) and the other end of the voltage source (1) In an image sensor comprising a common current-voltage conversion circuit (2), the other end of the common current output line (3) or the voltage source (1) and the second end of the second diode (Db1 to Db3) 1 impedance element (Ra1~Ra3 or Ca1~
An image sensor characterized in that a photodiode protection impedance element (6) is connected between the terminal on the side to which Ca3) is not connected. [2] The photodiode protection impedance element (6) has an impedance value larger than the input impedance of the current-voltage conversion circuit (2), and the plurality of first and second impedance elements are arranged in parallel. The image sensor according to claim 1, having an impedance value smaller than a composite impedance value. [3] Furthermore, the second diode (Db1 to Db3)
The image sensor according to claim 1 or 2, characterized in that a bias voltage source (7) is connected to a terminal on a side to which the first impedance element (Ra1 to Ra3 or Ca1 to Ca3) is not connected. .