JPH0646762B2 - 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.

[Problems to be Solved by the Related Art and Invention] An image sensor selects a plurality of photoelectric conversion elements for exchanging optical information with electric signals and a plurality of photoelectric conversion elements that are electrically scanned to select an electric signal. And an analog switch for obtaining the same. 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 an image sensor having an integrated circuit configuration,
The width of one photoelectric conversion element, that is, one pixel (for example, 125
One field effect transistor must be arranged so that it falls within the range of (μm). 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. Hei 1-1198279.

By the way, in the circuit of this application, a sawtooth wave is periodically added. Since the diode and the photodiode have capacitance, a discharge current flows when the sawtooth voltage becomes zero. This discharge current flows in the opposite direction to the normal current direction as shown by the broken line in FIG. 5 (B). The reverse output voltage due to this reverse current is an extra signal, and if it is output as it is, it must be removed by an external circuit that inputs and processes it. However, this circuit becomes complicated.

Then, the objective of this invention is providing the image sensor which can suppress the fluctuation | variation of the output voltage by a reverse current.

[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 the embodiments. A sawtooth wave that continuously or stepwise increases or decreases 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 the 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. To Da3, a first series circuit in which the first electrodes are arranged on the voltage source 1 side, and a first resistor or a capacitor Ra1 to Ra3 or Ca1 respectively.
.About.Ca3 and second diodes Db1 to Db3 connected in series, each of the first diodes Da1 to D1.
a2 connected to the second electrode of the a3 and the other end of the voltage source 1, and each of the second diodes Db1 ...
A plurality of second series circuits in which the respective second diodes Db1 to Db3 have directivity such that the forward current of Db3 flows based on the sawtooth wave, and the respective first diodes Da1 to Da3. The second electrode and the voltage source 1
A plurality of second resistors or capacitors Rb1 to Rb3 or C1 to C3 respectively connected to the other end of the first resistor Ra1 to Ra3 and the second diode Db1 to Db3. To P3 and the common current output line 3 for separating the plurality of photodiodes S1 to S3, which are respectively connected to each other with a directionality of reverse bias, and the plurality of photodiodes S1 to S3 from each other. In the image sensor, the blocking diodes Dc1 to Dc3 are connected to each other and the current-voltage conversion circuit 2 is connected between the common current output line 3 and the other end of the voltage source 1. A diode is connected between the output line and the ground so as to suppress a reverse voltage generated in the output line of the current-voltage conversion circuit when a reverse current flows through the current output line 3. The present invention relates to the image sensor.

[Operation] In the image sensor according to the present invention, when a current flows in the reverse direction in the common current output line 3, a voltage in the reverse direction to the normal state is generated in the output stage of the current-voltage conversion circuit 2 and the reverse voltage is absorbed. The reverse diode is turned on and the reverse voltage is absorbed.

[Embodiment] The one-dimensional image sensor according to the embodiment of the present invention shown in FIG. 1 includes a voltage source 1 and four unit circuits K0, K1, K2 and K3 corresponding to four pixels or bits. It has a current-voltage conversion circuit 2. This one-dimensional image sensor is configured to be able to detect a number of pixels greater than four. 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, and K3 that are identical to each other are
Diodes Da1, Da2, Da3 of the second diode D
b1, Db2, Db3, first resistors Ra1, Ra2, Ra3, second resistors Rb1, Rb2, Rb3, photodetection photodiodes S1, S2, S3, and blocking diode Dc.
It consists of 1, Dc2 and Dc3. Another unit circuit K0 arranged between the voltage source 1 and the unit circuit K1 includes a second diode Db0, a first resistor Ra0, a photodiode S0, and a blocking diode Dc0. The unit circuit K0 is the first of the other unit circuits K1, K2, K3.
Of the diodes Da1, Da2, Da3, and the second resistor Rb1,
It does not have one corresponding to Rb2 and Rb3. However, the unit circuit K0 can also be connected to the unit diodes K1, K2, and K3 corresponding to the first diode and the second resistor. Further, the unit circuit K0 of the first stage can be omitted from the image sensor of FIG. 1 if necessary. 3 having an anode (first electrode) and a cathode (second electrode)
One end (left end) of the circuit (first series circuit) in which the two first diodes Da1, Da2, Da3 are connected in series is connected to one end of the voltage source 1. First diode Da
1, Da2 and Da3 have the directivity to be 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. The first diode Da1,
Between the cathodes (second electrodes) of Da2, Da3 and the other end (ground) of the voltage source 1, first resistors Ra1, Ra2, Ra3 and second diodes Db1, Db2, Db3 are respectively connected in series. The connected circuits (second series circuits) are respectively connected. In the unit circuit K0, a series circuit of a first resistor Ra0 and a second diode Db0 is connected between one end and the other end of the voltage source 1. Second diodes Db0, Db
1, Db2 and Db3 have a directivity which is biased in the forward direction by the voltage of the voltage source 1.

The first resistors Ra0, Ra1, Ra2, Ra3 and the second diodes Db0, Db in each unit circuit K0, K1, K2, K3.
A series circuit (third series circuit) of photodiodes S0, S1, S2, S3 and blocking diodes Dc0, Dc1, Dc2, Dc3 is connected to interconnection points P0, P1, P2, P3 of 1, Db2, Db3. ing. That is, the cathodes of the photodiodes S0 to S3 are connected to the points P0 to P3, and the anodes thereof are blocking diodes Dc0, Dc1, Dc2, Dc3 for preventing mutual interference of the photodiodes S0 to S3.
Is connected to the common current output line 3 via.

The current-voltage conversion circuit 2 includes an operational amplifier 4 and a feedback resistor R.
f and a feedback capacitor Cf. Operational amplifier 4
The inverting input terminal of 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 and the capacitor Cf are provided between the inverting input terminal and the output terminal. It is connected. Therefore, the photodiodes S0-S3 are substantially in parallel with the second diodes Db0-Db3 and are reverse biased with the voltage of the voltage source 1. The output terminal of the operational amplifier 4 is connected to the voltage output terminal 5 via the inverting amplifier 4a.

The diode 7 connected between the output terminal of the operational amplifier 4 and the ground is a reverse voltage control diode according to the present invention, and is conductive when a reverse voltage is generated from the operational amplifier 4, that is, the current-voltage conversion circuit 2. Then, the output voltage is suppressed.

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 Db0 to Db3 in FIG.

The photodiodes S0 to S3 and the first diode Da1 to
Da3, the second diodes Db0 to Db3, and the blocking diodes Dc0 to Dc3 are PIN junction diodes, respectively, and include a hydrogenated amorphous silicon semiconductor layer, one electrode layer provided below the semiconductor layer, and a semiconductor. It is composed of the other electrode layer provided on the upper side of the layer, and is provided on a common insulating substrate (not shown).

Since the photodiodes S0 to S3 are reverse-biased, they are equivalently shown by the parallel circuit of the capacitance Cs and the current source Is proportional to the light intensity shown in FIG. In addition,
Equivalent capacitance Cs of the photodiodes S0 to S3
The value of the current flowing through is extremely small.

The first diodes Da1 to Da3 and the second diode Db0
The voltage across both ends, that is, the forward voltage Vf when Db3 is turned on is approximately 1V. The first resistors Ra0 to Ra3 each have a resistance of 100 kΩ, and the second resistors Rb1 to Rb3 each have a resistance of 1 kΩ, which are made of a material such as TiO ₂ , Ta—SiO ₂ or NiCr.

[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.
.About.Da3 are sequentially turned on. As the ramp voltage of the sawtooth wave gradually increases, the voltage Vp0 at the point P0 changes as shown in FIG.
It gradually increases as shown in. As a result, when the potential Vp0 at the point P0 becomes the forward voltage Vf of the second diode Db0 of the unit circuit K0, the diode Db0 is turned on,
The voltage Vp0 at the point P0 has a substantially constant value (approximately Vf), that is, a saturated voltage value. The first diode Da1 of the unit circuit K1 is also turned on almost at the same time as the second diode Db0 of the unit circuit K0 is turned on. First of unit circuit K1
In the period in which the diode Da1 is non-conducting (OFF state), the cathode of the first diode Da1 is approximately 0 volt, but the first diode Da1 is in the ON state, and the voltage Vd of the voltage source 1 is higher. Then, the cathode voltage of the first diode Da1 becomes higher following the voltage Vd. That is, when the first diode Da1 is turned on, the voltage across the first diode Da1 is almost fixed to the forward voltage Vf, so that the power supply voltage Vd
A voltage obtained by subtracting the forward voltage Vf of the diode Da1 from is applied to both ends of the second resistor Rb1. Also, the unit circuit K1
During the non-conduction period of the second diode Db1, the unit of the point P1 becomes substantially equal to the voltage across the second resistor Rb1. Therefore, after the first diode Da1 is turned on,
The potential Vp1 at the point P1 gradually rises as shown in FIG. When the potential Vp1 at the point P1 becomes the forward voltage Vf of the second diode Db1, this turns on and the point P1 is reached.
The potential Vp1 of the above becomes substantially constant (Vf). Unit circuit K1
The first diode Da2 of the unit circuit K2 is turned on almost at the same time as the second diode Db1 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 diode Da3 of the unit circuit K3 is turned on, and the potential Vp3 of FIG. 4A is obtained at the point P3. When the potentials Vp0 to Vp3 at the points P0 to P3 sequentially change as shown in FIG.
The photodiodes S0 to S3 connected between the P3 and the ground via the current-voltage conversion circuit 2 are sequentially driven. That is, the photodiodes S0 to S3 are electrically scanned.

In the circuit of FIG. 1, the photodiodes S0 to S3 are arranged one-dimensionally. This photodiode S0
When reading optical information in S3, first, the voltage source 1 generates a voltage capable of turning on all the first diodes Da1 to Da3 and the second diodes Db0 to Db3. The voltage for turning on all of the first diodes Da1 to Da3 and the second diodes Db0 to Db3 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 are
And all of the second diodes Da1 to Da3 and Db0 to Db3 can be turned on.

The first diodes Da1 to Da3 and the second diode Db0
During the period when all of Db3 to Db3 are on, the points P0 to P3 are
Forward voltage V of the second diodes Db0 to Db3 obtained at
Each photodiode S0 to S3 is reverse biased by f, and the capacitance Cs equivalently shown in FIG. 3 is charged. Since the equivalent capacitance Cs is extremely small, charging of the equivalent capacitance Cs can be achieved by a minute current in a region before the point where the forward current of the blocking diodes Dc0 to Dc3 rises sharply.

When an optical signal obtained from a subject (not shown) such as a facsimile document placed opposite the image sensor of FIG. 1 is input to the photodiodes S0 to S3, the presence or absence of the optical signal and the magnitude of the optical signal are detected. The charged charge amount of the equivalent capacitance Cs of the photodiodes S0 to S3 changes. That is, in the photodiodes S0 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. Equivalent capacitance C
The amount of discharge of s changes with the amount of light. There are two methods of giving an optical input to the photodiodes S0 to S3.
One of them is a method of always giving a light input to the photodiodes S0 to S3, and the other is a method of giving a light input only during a predetermined period (for example, a period when the voltage Vd of the voltage source 1 is 0 volt). is there.

When the voltage Vd of the voltage source 1 linearly increases with time as shown in FIG. 2, potentials Vp0, Vp1, Vp2 and Vp3 are obtained at points P0 to P3 as shown in FIG. 4 (A). Thus, the photodiodes S0 to S3 are sequentially reverse biased. In other words, the voltage for charging the equivalent capacitance Cs shown in FIG.
3 is applied. At this time, the photodiodes S0 to S3
In the equivalent capacitance Cs, the charging current flows to the one that is discharged by the light input, but the charging current does not flow to the one that is not discharged because there is no light input. Since the charging current of the equivalent capacitance Cs of the photodiodes S0 to S3 flows through the blocking diodes Dc0 to Dc3 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. In the state where each equivalent capacitance Cs is discharged because the light input is given to all of the four photodiodes S0 to S3, the potentials Vp0 to Vp3 shown in FIG. 4A are sequentially applied to the photodiodes S0 to S3. When applied, the voltage Vout at the output terminal 5 changes each time a charging current flows through the photodiodes S0 to S3, as shown in FIG. 4 (B). That is, as the potentials Vp0 to Vp3 of the points P0 to P3 increase, the charging current of the equivalent capacitance Cs increases, and when the potentials Vp0 to Vp3 of the points P0 to P3 become saturated, the charging current decreases and the change of the charging current. An output voltage Vout corresponding to is obtained.

In FIG. 4 (C), four photodiodes S0, S1,
No optical input is given to S2 of S2 and S3, and S0 and S3
The change in the voltage Vout of the output terminal 5 when the light input is given only to S1 and S3 is shown. In this case, the potentials Vp0 to Vp3 shown in FIG.
No charge current flows through the photodiode S2 when sequentially applied to S3. That is, the output voltage Vout corresponding to the potential Vp2 shown in FIG. 4 (A) does not change.

By the way, a positive direction output current Iout shown by an arrow in FIG. 1 flows from the voltage source 1 during a period in which a positive direction sawtooth wave is generated as shown in FIG. 5 (A). Further, the first diodes Da1 to Da3, the second diodes Db0 to Db3, the blocking diodes Dc0 to Dc3, and the photodiode S.
Each of 0 to S3 is a PIN diode, has an equivalent capacitance, and is charged when a sawtooth voltage is applied. When the sawtooth voltage becomes zero, the charge of each diode is discharged, and a current flows in the common current output line 3 in the opposite direction to the normal state. This reverse current path is composed of, for example, a blocking diode Dc1, a photodiode S1, a first resistor Ra1, a second resistor Rb1, an operational amplifier 4, a feedback resistor Rf, and a common current output line 3. When a reverse current flows through the common current output line 3, a reverse voltage is generated at the output terminal 5 as indicated by a broken line in FIG. Since the operational amplifier 4 is connected so as to function as an inverting amplifier, a negative voltage is generated at the output terminal of the operational amplifier 4 when the output terminal is normal, contrary to FIG. Occur. On the other hand, when the diode 7 according to the present invention is connected, when the output of the operational amplifier 4 becomes positive due to the reverse current, the diode 7 is turned on, and the output voltage of the operational amplifier 4 becomes the diode 7.
, And the output voltage Vout is correspondingly lowered. When the voltage due to the reverse current is suppressed, an external circuit for removing the voltage due to the reverse current becomes unnecessary.

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

(1) Connecting blocking diodes Dc0 to Dc3 for preventing mutual interference of the photodiodes S0 to S3 in series with the first resistors Ra0 to Ra3, or the second resistor Rb1.
~ Rb3 and the first resistors Ra1 to Ra3 can be connected.

(2) If the number of read pixels of the image sensor according to the embodiment is increased, the drive voltage Vd must be increased accordingly. Therefore, it is desirable to set the maximum number of read pixels to several tens. When the number of pixels is larger than this, the image sensor may be divided into a plurality of blocks and driven.

In FIG. 6, n unit circuits corresponding to the unit circuits K1 to K3 in FIG. 1 are m circuit blocks B1, B2 ... Bm.
Is divided into Each circuit block B1 to Bm has a first
The circuit includes several to several tens of units corresponding to the unit circuits K1 to K3 in the figure, and corresponds to a circuit in which the voltage source 1 is omitted from the image sensor circuit in FIG. Each circuit block B1 to B
m is connected to the voltage source 1a via the multiplexer 10. The output terminals of the circuit blocks B1 to Bm are commonly connected via the amplifiers A1 to Am. Voltage source 1a
Is generated by repeating the sawtooth wave (triangular wave) shown in FIG. The multiplexer 10 is shown in FIGS.
As shown in FIG. 7, the sawtooth wave of FIG. 7 (A) is distributed to the circuit blocks B1 to Bm. The light input to each photodiode of each circuit block B1 to Bm is always given as shown in FIG. 7 (D). The common current output line 3 of each block B1 to Bm is connected to the current-voltage conversion circuit 2 similar to that shown in FIG. 1, and the reverse voltage suppressing diode 7 is connected between this output line and the ground. As a result, blocks B1 to
It becomes possible to continuously take out the output of Bm.

8 and 9 show another driving method of the image sensor. Also in FIG. 8, n unit circuits corresponding to the unit circuits K1 to K3 in FIG. 1 are divided into m circuit blocks B1 to Bm just as in FIG. Each of the circuit blocks B1 to Bm is connected to the voltage source 1, respectively.
The voltage source 1 of FIG. 8 is similar to that of FIG.
Generates a sawtooth wave. The sawtooth wave is simultaneously supplied to the circuit blocks B1 to Bm as shown in FIGS. As a result, each circuit block B1 to Bm
The scanning starts at the same time, and outputs are generated at the same time. The output of each circuit block B1 to Bm is sent to the signal processing circuit 11 including a memory. The signal processing circuit 11 is a circuit block B1.
The outputs of .about.Bm are arranged on the common time axis so as to correspond to the arrangement order of the circuit blocks B1 to Bm. In the image sensor of FIG. 8, as shown in FIG. 9D, the light output to the photodiode is given during the period when the drive voltage Vd is zero.

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

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

(5) As shown in FIG. 12, the second resistor Rb1 shown in FIG.
Capacitors C1 to C3 may be connected instead of ~ Rb3. Further, the capacitors C1 to C3 in FIG. 12 can be replaced with diodes connected so as to be reverse biased. This diode functions as a capacitor.

(6) As shown in FIG. 13, the first resistor Ra0 of FIG.
It is also possible to replace -Ra3 with capacitors Ca1-Ca3. In this case, it is necessary to increase the leakage current of the second diodes Db0 to Db3 to form a capacitor discharge circuit.

(7) As shown in FIG. 14, a resistor 2a having a current-voltage conversion circuit connected between the current output line 3 and the ground.
The voltage of the resistor 2a may be input to the inverting amplifier 9 via the Bach amplifier 8 and the output of the inverting amplifier 9 may be output via the differentiating circuit including the capacitor C and the resistor R. In this case, the voltage suppressing diode 7 is connected between the output line of the inverting amplifier 9 and the ground.

(8) Voltage suppression diode 7 as shown in FIG.
In order to cancel this forward voltage Vf, a bias voltage line 7a having a value substantially the same as Vf can be connected in series.

(9) A dynamic range may be widened by connecting a power supply for applying a reverse bias voltage between the second diodes Db0 to Db3 and the ground.

(10) It is possible to use a circuit in which Db0, Ra0, S0 and Dc0 in the first stage are omitted.

[Effects of the Invention] As described above, according to the present invention, it is possible to suppress the voltage due to the reverse current and increase the operation speed of the image sensor.

[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 P0 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 the two photodiodes. FIG. 4 (C) shows a voltage change at the output terminal of the circuit of FIG.
Fig. 5 shows a state in which light is input to only three of the two photodiodes. Fig. 5 is a waveform diagram for explaining the relationship between the sawtooth wave and the output voltage. Fig. 6 shows the case where the number of unit circuits is large. 7 is a block diagram showing in principle the driving method of the photodiode of FIG. 7, FIG. 7 is a diagram showing the state of each part of FIG. 6, and FIG. 8 is a diagram showing the photodiode when the number of unit circuits is large as in FIG. FIG. 9 is a block diagram showing the driving method in principle, FIG. 9 is a diagram showing the state of each part of FIG. 8, and FIGS. 10 and 11 are waveform diagrams showing a modified example of a sawtooth wave, FIGS. 12 and 13. Is a circuit diagram showing a modification of the image sensor, FIG. 14 is a circuit diagram showing a modification of the current-voltage conversion circuit, and FIG. 15 is a circuit diagram showing a modification of the voltage suppression circuit. 1 ... Voltage source, Da1 to Da3 ... First diode, Db0
~ Db3 ... second diode, Ra0-Ra3 ... first resistance, Rb1-Rb3 ... second resistance, S0-S3 ... photodiode, 2 ... current-voltage conversion circuit, 7 ... voltage Suppression diode.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hiromi Kakinuma 6-16-20 Ueno, Taito-ku, Tokyo Within Taiyo Denki Co., Ltd. (72) Sadaaki Kurata 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Denki Co., Ltd. (72) Inventor Masanori Akagi 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka In-house (72) Inventor Hidetoshi Maeda 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Prefecture Sharp Corporation (72) In-house Mitsuhiko Yoshikawa, 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture

Claims (1)

[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. Each of the first diodes (Da1 to Da3) has a directionality such that the first diodes (Da1 to Da3) of the respective first diodes (Da1 to Da3) flow.
A first series circuit in which the electrodes of the first series circuit are arranged on the side of the voltage source (1), and a first resistor or capacitor (Ra1 to Ra3 or Ca1 to Ca3) and a second diode (Db1 to Db3) respectively. And a voltage source (1) composed of a circuit in which the first diode (Da1 to Da3) is connected and the second electrode of each of the first diodes (Da1 to Da3).
Is connected to the other end of the
A plurality of second series circuits, each second diode (Db1 to Db3) of which has a directivity such that a forward current of each diode (Db1 to Db3) flows based on the sawtooth wave. The second diode of the first diode (Da1 to Da3) of
A plurality of second resistors or capacitors (Rb1 to Rb3 or C1 to C3) respectively connected between the electrodes of the above and the other end of the voltage source (1), and the first resistors (Ra1 to Ra3). A plurality of photodiodes, each of which has a direction to be reverse biased and is connected between the connection point (P1 to P3) with the second diode (Db1 to Db3) and the common current output line (3). (S1-
S3), blocking diodes (Dc1 to Dc3) connected to each other to separate the plurality of photodiodes (S1 to S3) from each other, the common current output line (3) and the voltage source (1). And a current-voltage conversion circuit (2) connected between the other end of the current-voltage conversion circuit and the other end of the common-current output line (3) when a reverse current flows through the common current output line (3). An image sensor, wherein a diode is connected between the output line and the ground so as to suppress a reverse voltage generated in the output line.