JPH0570351B2 - - Google Patents

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 and problems to be solved by the invention] An image sensor includes multiple photoelectric conversion elements for converting optical information into electrical signals, and electrically scans the multiple photoelectric conversion elements to select an electrical signal. It also has an analog switch to obtain the desired results. The analog switch is made of a field effect transistor (FET), for example, as disclosed in Japanese Patent Application Laid-Open No. 63-2377, and is arranged near a plurality of photoelectric conversion elements.

By the way, in an integrated circuit image sensor, one field effect transistor must be arranged to fit within the width (for example, 125 μm) of one photoelectric conversion element, that is, one pixel. 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 kind of problem, a method of scanning photodiodes using a series circuit of diodes was proposed in Japanese Patent Application No. 190848/1984 and Japanese Patent Application No. 198279/1999, which is an application claiming domestic priority. Disclosed. However, a specific method for obtaining accurate output is not disclosed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image sensor that can effectively extract optical information stored in a photodiode.

[Means for Solving the Problems] To achieve the above object, the present invention provides a sawtooth wave that increases or decreases continuously or stepwise with time. It is a circuit in which a voltage source 1 for activating a voltage source 1 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. and the directionality is 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
A first series circuit in which the first electrode of ~Da3 is arranged on the side of the voltage source 1, and a first impedance element Ra1~Ra3 or Ca1~, respectively;
It consists of a circuit in which Ca3 and second diodes Db1 to Db3 are 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 a plurality of second series circuits in which each of the second diodes Db1 to Db3 has a directionality such that a forward current of each of the second diodes Db1 to Db3 flows based on the sawtooth wave; a plurality of second impedance elements Rb1 to Rb3 or C1 to C3 respectively connected between the second electrode of each of the first diodes Da1 to Da3 and the other end of the voltage source 1; impedance element
A plurality of photodiodes S1 to S are respectively connected between respective connection points _P1 to P3 of Ra1 to Ra3 or Ca1 to Ca3 and second diodes Db1 to _Db3 and the common current output line ₃ . ₃ , and a path through which the current of the photodiodes _S1 to S3 flows in a direction opposite to that of the photodiodes _{S1 to S3 in} order to prevent mutual interference among the plurality of photodiodes _S1 to _S3 . multiple blocking diodes connected to
A common current connected between Dc1 to Dc3 and the common current output line 3 and the other end of the voltage source 1 -
The present invention relates to an image sensor comprising a voltage conversion circuit 2 in which the input impedance Zif of the current-voltage conversion circuit 2 is smaller than the floating impedance Zb of the input of the current-voltage conversion circuit 2.

Note that when the blocking diodes Dc1 to Dc3 are connected in series to the photodiodes _S1 to _S3 , it is desirable to set the input impedance Zif to 1/2πCdc(n-1) or less. In the above formula, the driving frequency of photodiodes S ₁ to _{S 3} is
Cdc is the equivalent capacitance of each of the blocking diodes Dc1 to Dc3, and n is the blocking diode
This is the number of Dc1 to Dc3.

In addition, the current-voltage conversion circuit 2 includes a feedback resistor
It is preferable to configure the operational amplifier 4 with R and a feedback capacitor C. In this case, it is desirable to set RC≦1/.

[Function] When configured according to the present invention, the photocharges accumulated in the photodiodes S ₁ to S ₃ can be effectively converted into current-voltage.

Setting as shown in claim 2 enables current-voltage conversion with less influence of leakage current passing through a photodiode that is not scanned.

According to claim 3, current-voltage conversion with a good S/N ratio can be performed without oscillation.

[Embodiment] A one-dimensional image sensor according to an embodiment of the present invention shown in FIG. 1 includes a voltage source and four unit circuits K ₀ , K ₁ , corresponding to four pixels or bits.
K ₂ , K ₃ and a current-voltage conversion circuit 2.
This one-dimensional image sensor is configured to be able to detect more than four 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 K ₁ , K ₂ , K ₃ are
First diodes Da1, Da2, Da3, second diodes Db1, Db2, Db3, and first resistor
Ra1, Ra2, Ra3 and second resistors Rb1, Rb
2, Rb3 and photodiode S ₁ for photodetection,
S ₂ , S ₃ and blocking diode Dc1, Dc
2, 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.
It consists of Dc0. Unit circuit K ₀ is another unit circuit
The first diode Da1 in K ₁ , K ₂ , K ₃ ,
Da2, Da3, and second resistors Rb1, Rb2, Rb
It does not have anything corresponding to 3. However, the unit circuit K ₀ can also be connected with those corresponding to the first diode and second resistor of other unit circuits K ₁ , K ₂ , K ₃ . Furthermore, the first stage unit circuit K ₀ can be omitted from the image sensor shown in FIG. 1 if necessary.

three first diodes Da1 having an anode (first electrode) and a cathode (second electrode);
One end (left end) of a circuit in which Da2 and Da3 are connected in series with each other (first series circuit) is connected to one end of the voltage source 1. First diode Da1, Da
2, Da3 has a directionality that is biased in the forward direction 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. 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.

The cathodes (second electrodes) of the first diodes Da1, Da2, Da3 and the other end (ground) of the voltage source 1
between the first resistors Ra1, Ra2, Ra3 as the first impedance elements and the second diode.
A circuit (second series circuit) in which Db1, Db2, and Db3 are connected in series is connected to each other. 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. The second diodes Db1, Db2, and Db3 have directionality that is forward biased by the voltage of the voltage source 1. The second resistors Rb1 to Rb3 as second impedance elements are connected to the first diodes Da1 to Da.
It is connected between the cathode of No. 3 and ground.

The interconnection point P ₀ of the first resistor Ra0, _{Ra1, Ra2, Ra3 and the second diode Db0, Db1, Db2, Db3 in each unit circuit K 0 , K 1} , K 2 , K 3 ,
Photodiode S ₀ , S ₁ , S ₂ , S ₃ at P ₁ , P ₂ , P ₃
and blocking diodes Dc0, Dc1, Dc2,
A series circuit with DC3 (third series circuit), that is, the cathodes of the photodiodes _S0 to _S3 are connected to the points _P0 to _P3 , and the anodes are connected to the points _P0 to P3 to prevent mutual interference of the photodiodes S0 to _S3 . blocking diode
It is connected to a common current output line 3 via Dc0, Dc1, Dc2, and Dc3.

The current-voltage conversion circuit 2 includes an operational amplifier 4, a feedback resistor R, and a feedback capacitor C. 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 R and capacitor C are connected to the inverting input terminal and the output terminal. connected between. The output terminal of the operational amplifier 4 is connected to the output terminal 5 via an inverting amplifier 4a. Note that photodiodes S ₀ to S ₃ are second diodes.
It is substantially connected in parallel to Db0 to Db3. Further, the photodiodes S ₀ to _{S 3} are connected so as to be reverse biased by the voltage of the voltage source 1 . Therefore, the current flowing through the photodiodes _S0 to _S3 is extremely small.

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.
It is set to a value that can turn on 0 to Da3 and Db0 to Db3.

Photodiodes _S0 to _S3 , first diode
Da1 to Da3, second diode Db0 to Db3,
The blocking diodes Dc0 to Dc3 are pin junction diodes, and each includes a hydrogenated aluminous silicon semiconductor layer, one electrode layer provided below this semiconductor layer, and an electrode layer provided above the semiconductor layer. and the other electrode layer, and are provided on a common insulating substrate (not shown).

Since the photodiodes _S0 to _S3 are reverse biased, they are equivalently represented by a parallel circuit of a capacitance Cs and a current source Is proportional to the light intensity shown in FIG. Note that the value of the current flowing through the equivalent capacitance Cs of the photodiodes _S0 to _S3 is extremely small.

When the first diodes Da1 to Da3 and the second diodes Db0 to Db3 are turned on, the voltage across them, that is, the forward voltage V is approximately 1V. The first resistors Ra0 to Ra3 are each 100kΩ, and the second
The resistances Rb1 to Rb3 are each 1 kΩ, and are made of a material such as TiO ₂ , Ta-SiO ₂ or NiCr.

[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 diodes Da1 to Da3 sequentially become conductive. First, when the sawtooth wave ramp voltage gradually increases, the first diode Da1 of the unit circuit _K1 also turns on. During the period when the first diode Da1 of the unit circuit _K1 is non-conducting (off state), the cathode of the first diode Da1 is at almost zero volts, but when the first diode Da1 is on state, the voltage is further increased. When the voltage Vd of the source 1 increases, the cathode potential of the first diode Da1 increases following the sawtooth voltage Vd. That is, when the first diode Da1 is turned on, the voltage across it is almost fixed to the forward voltage V, so the voltage obtained by subtracting the forward voltage V of the diode Da1 from the power supply voltage Vd is the voltage across the second resistor Rb1. Add to both ends. Also, the second diode Db1 of the unit circuit _K1
During the period when P is non-conducting, the potential at point _P1 becomes the second resistor.
It becomes almost equal to the voltage across Rb1. Therefore, after the first diode Da1 is turned on,
The potential Vp1 at point _P1 gradually rises as shown in FIG. 4A. The potential Vp1 at point _P1 is the second diode
When the forward voltage of Db1 reaches V, it turns on, and the potential Vp1 at point _P1 is approximately constant (V)
become. Almost at the same time as the second diode Db1 of the unit circuit _K1 turns on, the first diode Da2 of the unit circuit _K2 turns on, and the point _P2
As shown in FIG. 4A, a potential Vp2 is obtained.
When the sawtooth ramp voltage supplied from the voltage source 1 increases further, the first diode Da3 of the unit circuit _K3 turns on, and the potential Vp3 of FIG. 4A is obtained at the point _P3 . Potential VP0 of points P ₀ to P ₃
When ~ _VP3 changes _sequentially as shown in FIG.
S ₀ to S ₃ are sequentially driven. That is, photodiodes _S0 to _S3 are electrically scanned.

In the circuit of Fig. 1, photodiodes _S0 to _S3
are arranged one-dimensionally. When reading optical information with these photodiodes _S0 to _S3 , first, a voltage that can turn on all of the first diodes Da1 to Da3 and the second diodes Db0 to Db3 is generated from the voltage source 1. . In addition, the first
diodes Da1 to Da3 and a second diode
The voltage for turning on all Db0 to Db3 can be given by 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 Db0 to Db3 can be turned on.

During the period when all of the first diodes Da1 to Da3 and the second diodes Db0 to Db3 are in the on state, the second diode Db obtained at the points _P0 to _P3
Each photodiode S0 to _S3 is reverse biased by a forward voltage V of ₀ to Db3, and a capacitance Cs equivalently shown in FIG. 3 is charged. In addition,
Since the equivalent capacitance Cs is extremely small, charging of the equivalent capacitance Cs can be achieved by a minute current in the region before the point at which the forward current of the blocking diodes Dc0 to Dc3 rises sharply.

An optical signal obtained from an object (not shown), such as a facsimile document, which is placed opposite to the image sensor in FIG _.
When input to ~ _S3 , the amount of charge in the equivalent capacitance Cs of the photodiodes _S0 to _S3 changes depending on the presence or absence and magnitude of the optical signal. That is, among the photodiodes S ₀ to _{S 3} , discharge of equivalent capacitance Cs occurs in those to which an optical signal is input, and discharge of equivalent capacitance Cs does not occur in those to which no optical signal is input. equivalent capacitance Cs
The amount of discharge varies depending on the amount of light. There are two methods for providing optical input to the photodiodes _S0 to _S3 . One is to always provide optical input to the photodiodes S ₀ to _{S 3} , and the other is to provide optical input only during predetermined periods (for example, periods when the voltage Vd of voltage source 1 is 0 volts). It's a method.

When the voltage Vd of the voltage source 1 increases linearly with time as shown in FIG. 2, potentials Vp0, Vp1, Vp2, Vp3 appear at points _P0 to _P3 as shown in FIG. 4A.
is obtained, which makes the photodiode S ₀ ~
S ₃ is sequentially reverse biased. In other words, the third
A voltage is applied to the photodiodes S ₀ -S ₃ to charge the equivalent capacitance Cs shown in the figure.
At this time, a charging current flows to those of the equivalent capacitance Cs of the photodiodes S ₀ to _{S 3} that are discharged due to optical input, but a charging current flows to those that are not discharged due to no optical input. Not flowing. The charging current of the equivalent capacitance Cs of the photodiodes _S0 to _S3 is the same as the blocking diode Dc0 to Dc3.
flows through the current-voltage conversion circuit 2,
The voltage Vout of output terminal 5 depends on the presence or absence of charging current.
changes. In a state where each equivalent capacitance Cs is discharged because optical input is given to all four photodiodes _S0 to _S3 , Fig. 4A
The potentials Vp0 to Vp3 shown in are the photodiodes S ₀ to
When applied sequentially to S ₃ , the voltage at output terminal 5
Vout is a photodiode as shown in Figure 4B.
It changes every time the charging current flows through S ₀ to _{S 3} . That is,
As the potentials Vp0 to Vp3 at each point _P0 to _P3 increase, the charging current of the equivalent capacitance Cs increases, and each point
When the potentials Vp0 to Vp3 of _P0 to _P3 are saturated, the charging current decreases, and an output voltage Vout corresponding to this change in charging current is obtained.

Figure 4C shows four photodiodes S ₀ , S ₁ ,
No optical input is given to S ₂ of S ₂ and S ₃ , and S ₀ , S ₁ ,
The change in the voltage Vout at the output terminal 5 when optical input is applied only to _S3 is shown. In this case,
When the potentials Vp0 to Vp3 shown in FIG. 4A are sequentially applied to the photodiodes _S0 to _S3 , no charging current flows through the photodiode _S2 . That is, a change in the output voltage Vout corresponding to the potential Vp2 shown in FIG. 4A does not occur.

Next, the operation of the current-voltage conversion circuit 2 will be explained. The current Iout of the common current output line 3 flows through the feedback resistor R of the current-voltage conversion circuit 2. Therefore, an output voltage Vout is generated which is Iout multiplied by R.
However, if the floating impedance Zb between the inverting input terminal of the operational amplifier 4 and the common current output line 3 and the ground is smaller than the input impedance Zif of the current-voltage conversion circuit 2, the output current will pass through the floating impedance Zb. As a result, the output voltage Vout becomes small and the S/N ratio deteriorates. In other words, the input impedance of the current-voltage conversion circuit 2
Zif and floating impedance Zb are approximately expressed by the following equations.

Zif≒R/A Here, A is the open loop gain of the operational amplifier 4.

Zb≒1/2π(n-1)Cdc Here, n is the number of blocking diodes connected to the common current output line 3, Cdc is the equivalent capacitance of the blocking diodes Dc0 to Dc3, and is the current Iout. This is the frequency, that is, the driving frequency of the photodiodes _S0 to _S3 .

The formula showing the stray impedance Zb is the equivalent capacitance Cdc of the blocking diodes Dc0 to Dc3 compared to each equivalent capacitance Cs of the photodiodes _S0 to _S3 and each equivalent capacitance Cb of the second diodes Db0 to Db3
is significantly small, the photodiodes _S0 to _S3 and the second diodes Db0 to Db3 are ignored to approximate the floating impedance. The floating impedance Zb is the n-1 unit circuit (bit) remaining after excluding one photodiode during scanning.
occurs in

The current Iout flowing through the common current output line 3 is expressed as K in the following equation.
The current KIout multiplied by KIout flows into the current-voltage conversion circuit 2 and is effectively converted into a voltage.

K=Zb/Zif=A/2π(n-1)CdcR Therefore, the larger the value of K, the better. In particular, the open loop gain A has frequency dependence and becomes smaller as the frequency becomes higher. Therefore, the higher the frequency of the current component, the less it flows into the current-voltage conversion circuit 2 and instead flows into the floating impedance Zb.
Therefore, in order to faithfully convert the high frequency component of the output current Iout from current to voltage, it is necessary that at least Zb/Zif≧1, in other words, Zif≦1/2π(n-1)Cdc. desirable.

On the other hand, in order to prevent oscillation caused by the operational amplifier 4, it is necessary to connect a capacitor C in parallel to the feedback resistor R. When the capacitor C is connected, the current with a frequency component higher than the frequency corresponding to the reciprocal 1/RC of the time constant RC is no longer effectively converted into voltage by the current-voltage conversion circuit 2. Therefore, it is desirable to set 1/RC higher than the drive frequency.

As described above, according to this embodiment, the photodiodes _S0 to Sn can be sequentially driven (scanned) using diodes without using transistors. Diodes are easier to manufacture than field-effect transistors because they do not require a gate electrode. For example, when the bit spacing is 125 μm, the width of the wiring conductor is 20 μm.
It becomes possible to do the above, and the manufacturing yield is greatly improved. In addition, when the switch element is constituted by a field effect transistor, it is necessary to set the width of the wiring conductor to about 10 μm.

In addition, by setting the input impedance Zif, feedback resistor R, and capacitor C to satisfy the above conditions, the stray impedance Zb
Output voltage due to signal current Iout flowing into
It is possible to prevent a decrease in Vout, that is, a decrease in the SN ratio.

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

(1) Blocking diodes Dc0 to Dc3 for preventing mutual interference of photoelectric conversion elements S ₀ to S ₃ are connected in series to the first resistors Ra0 to Ra3, or connected to the second resistors Rb1 to Rb3. First resistance Ra1
~Ra3.
In this case, the floating impedance Zb is determined by the equivalent capacitance Cs of the photodiodes _S0 to _S3 and the equivalent capacitance Cb of the second diodes Db0 to Db3.

(2) When the image sensor shown in FIG. 1 is used in a facsimile machine, it is necessary to provide, for example, 2000 units corresponding to the unit circuits K ₀ to K ₃ .
The maximum value of the sawtooth wave for simultaneously turning on a large number of diodes corresponding to the first diodes Da1 to Da3 and the second diodes Db0 to Db3 becomes extremely high. 5 and 6 show one method by which the maximum voltage of the voltage source 1 can be kept low. In FIG. 5, n unit circuits corresponding to unit circuits _K0 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 unit circuits corresponding to the unit circuits _K0 to _K3 in FIG.
This corresponds to a circuit in which . Each circuit block B1-Bm is connected via a multiplexer 10 to a voltage source 1a. The output terminals of each circuit block B1-Bm are commonly connected via amplifiers A1-Am. The voltage source 1a repeatedly generates a sawtooth wave (triangular wave) shown in FIG. 6A. The multiplexer 10 is shown in FIG. 6B,
As shown in FIG. 6C, the sawtooth wave of FIG. 6A is distributed to circuit blocks B1 to Bm. Optical input to each photodiode of each circuit block B1-Bm is always provided as shown in FIG. 6D.

(3) As shown in Figure 7, the second resistors Rb1 to Rb3 as the second impedance elements in Figure 1
and can be replaced with capacitors C ₁ to _{C 3} that are sufficiently larger than the equivalent capacitance of the photodiodes S ₀ to _{S 3} . Also, the capacitor C ₁ ~ in Figure 7
A diode may be connected in place of C ₃ so as to be reverse biased, and this diode may be used as the equivalent capacitance.

(4) As shown in Figure 8, the first resistors Ra0 to Ra3 as the first impedance elements in Figure 1
can be replaced with capacitors Ca0 to Ca3 that are larger than the equivalent capacitance of the photodiodes _S0 to _S3 . Also, the capacitor in Figure 8
Ca0-Ca3 can be replaced with reverse biased diodes that function equivalently.

(5) Replace the first resistors Ra0 to Ra3 in Figure 1 with a first capacitive element consisting of a capacitor or reverse bias diode, and replace the second resistor Rb1
~Rb3 can be replaced by a second capacitive element consisting of a capacitor or a reverse bias diode. 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. 9, or a sawtooth wave that increases in a quadratic curve as shown in FIG.

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

(8) In the example, diodes Da1~Dan, Db0~
Although hydrogenated amorphous silicon (amorphous silicon) was used as Dbn, amorphous silicon carbide or the like may also be used.

(9) Diode Da1~Dan, Db0~Dbn, Dc0
~Dcn may be any of PIN, PI, IN, Schottky junction diode, etc.

(10) A voltage may be applied to the cathode terminals of the second diodes Db0 to Dbn. That is, a bias power supply may be connected between the ground and the cathodes of the second diodes Db0 to Db3. This makes it possible to expand the dynamic range.

(11) The first and second impedance elements may be configured with any one of a resistor, a capacitor, or a diode, or may be configured by connecting these in series or in parallel.

(12) In FIG. 1, the value of the second resistor may be set to gradually increase from Rb1 to Rbn. That is, Rb1<Rb2...<Rbn may be set.

[Effects of the Invention] As described above, according to the present invention, an image sensor with a simple configuration can be provided. Further, signals can be effectively extracted from the photodiode.

[Brief explanation of the drawing]

Fig. 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. 4A is the circuit of Fig. 1. _FIG . _4B is a diagram showing voltage changes at the output terminal of the circuit in FIG. 1 with optical input applied to all four photoelectric conversion elements. Figure 4C shows the voltage change at the output terminal of the circuit in Figure 1 when only three of the four photoelectric conversion elements receive optical input, and Figure 5 shows the voltage change at the output terminal of the circuit in Figure 1 when there are many unit circuits. 6 is a diagram showing the state of each part of FIG. 5, FIGS. 7 and 8 are circuit diagrams showing a modified example of the image sensor, and FIG. and FIG. 10 are waveform diagrams showing modified examples of sawtooth waves. 1...Voltage source, Da1~Da3...Diode, Ra1
~Ra3...first resistor, Rb1~Rb3...second resistor, _S1 ~ _S3 ...photodiode, 2...current-voltage conversion circuit.

Claims (1)

[Claims] 1. A voltage source 1 for supplying a sawtooth wave that increases or decreases continuously or stepwise with time, and a plurality of first voltage sources each having a first electrode and a second electrode. A circuit connected in series with diodes Da1 to Da3, one end of which is connected to the voltage source 1, and each first diode Da
Each of the first diodes Da1 to Da3 has a directionality such that a forward current of 1 to Da3 flows based on the sawtooth wave, and
a first series circuit in which the first electrodes of the diodes Da1 to Da3 are arranged on the side of the voltage source 1, and each of the first impedance elements Ra1 to
Ra3 or Ca1~ca3 and second diode Db1~
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 diodes Db1 ~
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 Db3 flows based on the sawtooth wave; a plurality of second impedance elements each connected between the second electrode and the other end of the voltage source 1;
Rb1 to Rb3 or C1 to C3 , and the first impedance element (Ra1 to Ra3
or Ca1 to Ca3) and the second diode Db1
A plurality of photodiodes S1 to S3 each connected between respective connection points _P1 to _P3 with ~Db3 and _the common current output line ₃ ; and the plurality of photodiodes S1 _{to S3} . A plurality of blocking diodes Dc1 to Dc1 have opposite directionality to the photodiodes _{S1 to S3 and} are connected to the paths through which the currents of the photodiodes _S1 to _S3 flow in order to prevent mutual interference of the photodiodes S1 to S3. Dc3, 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.
An image sensor comprising: An input impedance Zif of the current-voltage conversion circuit 2 is made smaller than an input floating impedance Zb of the current-voltage conversion circuit 2. 2. The blocking diodes Db1 to Db3 are connected in series to the photodiodes _S1 to _S3 , and the input impedance Zif is 1/2πCdc(n-1) (where, is the drive of the photodiodes) 2. The image sensor according to claim 1, wherein the frequency and Cdc are set as follows (wherein the equivalent capacitance of the blocking diode and n is the number of the blocking diodes). 3. The current-voltage conversion circuit 2 includes: an operational amplifier 4 whose inverting input terminal is connected to the common current output line 3 and whose non-inverting input terminal is connected to the other end of the voltage source 1; and the operational amplifier 4. A feedback resistor R connected between one input terminal and an output terminal of the feedback resistor R, and a feedback capacitor C connected in parallel to the feedback resistor R, and The product RC of the values of the feedback capacitor C is 1/(however,
(2) is set to a value equal to or lower than the driving frequency of the photodiode.
The image sensor described.