JPH0444461A - Image sensor - Google Patents

Abstract

PURPOSE:To prevent mutual interference of outputs of plural sensor groups by providing a common current output line of the sensor group to each of even number order sensor group and of an odd number order sensor group, processing a signal for each common current output line, combining signals and extracting an output signal of the sensor groups continuously. CONSTITUTION:To apply a sawtooth wave voltage (search voltage) to a power terminal l, lst and 2nd sawtooth wave generating circuits 4, 5 are provided. A common current output line 3 of odd number order sensor groups B1, B3 to B(n-1) is connected to a lst synthesis current output line 9 and a common current output line 3 of even number order sensor groups B2, B4 to Bn is connected to a 2nd synthesis current output line 10. Output terminals of lst and 2nd current-voltage conversion circuits are connected to a multiplexer 19 as a synthesis circuit via lst and 2nd inverse amplifiers 17, 18. The multiplexer 19 is controlled by a timing control circuit 6 to extract alternately outputs of the lst and 2nd inverse amplifiers 17, 18 and to send a sensor output voltage Vo to a common output terminal 20.

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.

[Problems to be solved by the prior art and the invention 1 Image sensors include a plurality of photodiodes for exchanging optical information into electrical signals, and a method for electrically scanning the plurality of photodiodes to selectively convert the electrical signals. It has an analog switch to obtain.

Analog switches are, for example, field effect transistors (F
ET) and is arranged near a plurality of photodiodes.

By the way, in an image sensor with an integrated circuit configuration,
The width of one photodiode or one pixel (e.g. 1
One field effect transistor must be placed to fit within 25 μm). 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.

To solve this kind of problem, Japanese Patent Application No. 1-198279 discloses a method of scanning a photodiode using a sawtooth voltage and a series circuit of diodes. In this method, as the number of photodiodes to be scanned increases, the maximum amplitude value of the sawtooth voltage inevitably increases, making manufacturing difficult. For this reason, the above-mentioned application discloses a method in which a large number of photodiodes are divided into groups and scanned. However, the technique for relating multiple sensor groups to each other is not explained in detail.

In the scanning method disclosed in the above application, the scanning diode, the photodiode as a sensor, and the blocking diode to prevent mutual interference have capacitance, so the sawtooth voltage applied to them is zero. When this happens, a discharge current flows, and this discharge current flows in the opposite direction to the normal current. When this current value becomes large, the output of the previously scanned sensor group has a negative effect on the output of the later scanned sensor group. Note that this will be explained in more detail in the examples.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image sensor that can prevent mutual interference of outputs from a plurality of sensor groups.

[Means for Solving the Problems] The present invention for achieving the above object will be described with reference to the reference numerals in the drawings showing the embodiments. A plurality of first diodes D a each having a first electrode and a second electrode
l - D a3 are connected in series, one end of which is connected to the power supply terminal l, and a direction in which the forward current of each of the first diodes Dal to Da3 flows based on the scanning voltage. a first series circuit in which each of the first diodes Da1 to Da3 has a characteristic, and the first electrode of each of the first diodes Dal to Da3 is disposed on the side of the power supply terminal 1; Each has a first resistor Rat-Ra8 and a second diode Db1.
~Db3 connected in series, each connected between the second electrode of each of the first diodes Dal~Da3 and the common terminal 2, and each of the second diodes Db1~Db3 A plurality of second diodes Db1 to Db3 each have a directionality such that a forward current flows based on the scanning voltage.
and the respective first diodes Dal~D
a3, a plurality of second resistors Rbl to Rb3 respectively connected between the second electrode and the common terminal 2, the common current output line 3, the first resistors Ra1 to Ra8 and the second Connection points P1 to P3 with diodes Db1 to Db3
and the common current output line 3, a plurality of photodiodes S1 to S3 are connected with each other in a reverse-biased direction, and the plurality of photodiodes 81 to
In an image sensor in which a plurality of sensor groups are formed with blocking diodes Del-Dc3 connected between each other to separate S8 from each other, and the sensor groups are driven in a time-sharing manner, the common current of the sensor groups is Output line (
3) is provided for each even-numbered sensor group and odd-numbered sensor group, and after signal processing is performed for each common current output line, the signals are combined so that the output signals of the sensor groups can be continuously extracted.

[Function] The plurality of sensor groups of the present invention are time-divisionally driven, and outputs are extracted separately into odd-numbered and even-numbered sensor groups. Therefore, interference between the outputs of the sensor group is reduced, and outputs with good continuity can be obtained.

C. First Embodiment Next, a one-dimensional image sensor according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4.

This image sensor has a plurality of sensor groups B1 to Bn, as shown in FIG. Each sensor group Bl-Bn, for example, when configuring a facsimile image sensor, consists of 2,000 photodiodes arranged geometrically in a straight line and divided into groups of several to hundreds of photodiodes. be.

FIG. 2 shows a specific configuration of the first to n-th sensor groups BL to Bn in FIG. 1. Each sensor group Bl-B'n is
It has a sawtooth voltage application power supply terminal 1, a common terminal (ground terminal) 2, four sensor unit circuits KO, Kl, K2, Kg corresponding to four pixels or bits, and a common current output line 3. This sensor group is configured to be able to detect more than four pixels. However, since it is difficult to show all of these structures in the drawings, only a part of them is shown in FIG.

Three mutually identical unit circuits Kl, K2, K3 are:
First diodes D al, D a2, Da8, second diodes Dbl, Db2, Db3, first resistors Ra1SRa2, Ra3, and second resistors Rb1SRb2
, Rb3, and a photodiode 5ISS2 for photodetection,
S8 and booking diodes Del, Dc2, Dc
It consists of 3. Another unit circuit KO includes a second diode DbO, a first resistor RaO, a photodiode SO, and a blocking diode DcO.

The unit circuit KO includes, in another unit circuit, first diodes D aL D a2, Da3 at 1, K2, Kg, and second resistors Rb1 . , Rb2, and Rb8.

Three first diodes Dal, Da2, Da3 having an anode (first electrode) and a cathode (second electrode)
One end (left end) of a circuit (first series circuit) in which these are connected in series with each other is connected to a power supply terminal 1. The first diodes Dal, Da2, and Da3 have directivity that is biased in the forward direction by the sawtooth voltage supplied from the power supply terminal 1.

That is, the anodes (first electrodes) of the first diodes Da1 to Da3 are arranged on the power supply terminal 1 side. Note that when the power supply terminal 1 is negative, the first diode Dal
The cathode of ~Da3 is arranged on the power supply terminal 1 side. First resistors RaL, Ra2, Rag and a second diode D are connected between the cathodes (second electrodes) of the first diodes Dal, Da2, Da3 and the common terminal (ground terminal) 2.
A circuit (second series circuit) in which bL, Db2, and Db3 are connected in series is connected to each other. Second diode D bl.

Db2 and Db3 have directionality that is biased in the forward direction by the sawtooth voltage of the power supply terminal 1.

The unit circuit KO is also configured in substantially the same manner as the other unit circuits 1 to 3.

Each unit circuit KG SKl, K2, K! The interconnection point P of the first resistor Ra01Rat, Ra2, Ra3 and the second diode DbO1Dbl, Db2, Db3 at l
Photodiodes So and SL are connected to O1PL, P2, and P3.

S2, S3 and blocking diode DeO1Del,
A series circuit (third series circuit) with Dc2 and Dc3 is connected. That is, the cathodes of the photodiodes SO to S8 are connected to the point PO-Pa, and the anodes are connected to the common current output line 3 via blocking diodes DcO1Del, Dc2, and Dc8 to prevent mutual interference of the photodiodes SO to S3. has been done.

In order to configure a -dimensional image sensor, the photodiodes SO to S3 are arranged in a straight line, and all the photodiodes in each group Bl-Bn in FIG. 1 are also arranged in series.

In order to supply a sawtooth wave voltage (scanning voltage) to the power supply terminal 1 of FIG. 2, first and second sawtooth wave generation circuits 4.5 are provided as shown in FIG. 1. 1st and 2nd
The sawtooth wave generation circuit 4.5 is controlled by the timing control circuit 6 to generate first and second sawtooth wave voltages (triangular waves) Vl and V2 shown in FIGS. 4(A) and 4(B). The first sawtooth wave generation circuit 4 generates a sawtooth wave (triangular wave) during a period from t1 to t3, then has a rest period from t3 to t5, and then generates a sawtooth wave again from t5 to t9. That is, a sawtooth wave having a period T is repeatedly generated.

The second sawtooth wave generation circuit 5 generates a second sawtooth wave voltage v2 shown in FIG. 4(B) having a phase difference (delay time) Td with respect to the first sawtooth wave voltage Vl of FIG. 4(A). is generated with a period T. That is, in this embodiment, the ramp voltage of the second sawtooth voltage v2 rises in synchronization with the ramp voltage section tl - t2 of the first sawtooth voltage v1 and the end times t2 and t8 from t5 to t8, The ramp voltage section ends at the rising time t5, tlO of the sawtooth voltage Vl.

The first sawtooth wave generation circuit 4 connects the odd-numbered sensor groups Bl, B8, . . . B n via the first multiplexer 7
-1 are selectively connected to each power supply terminal 1.

That is, the first multiplexer 7 is controlled by the timing control circuit 6 to generate the first sawtooth voltage 1 shown in FIG. 4(A).
The section from t1 to t5 of 1 is extracted and given to the first sensor group B1, and the section from t5 to t10 is extracted and given to the third sensor group B.
S, the sawtooth wave of FIG.

B3...Distribute to Bn-1.

The second sawtooth wave generating circuit 5 is selectively connected to the power supply terminals 1 of the even-numbered sensor groups B2, B4, . . . Bn via the second multiplexer 8. That is, the second multiplexer 8 is controlled by the timing control circuit 6 to
The section t2 to t8 of the sawtooth wave voltage v2 in Figure (B) is extracted and applied to the second sensor group B2, and the sawtooth wave generated from t8 is applied to the fourth sensor group B4.
) sawtooth wave from even numbered sensor groups B2, B4...
Give to Bn.

Note that the first multiplexer 7 causes the
tl-t2, t5 to t8, etc., and the second multiplexer 8 extracts t2 in FIG. 4(B).
It is also possible to extract only the slope voltage sections from t5 to t8 to tlO and distribute it to each sensor group Bl-Bn.

Odd-numbered sensor groups Bl, B3...Bn- in FIG.
The common current output line 3 of No. 1 is connected to the first combined current output line 9, and the common current output line 3 of even-numbered sensor groups B2, B4...Bn is connected to the second combined current output line 10. has been done.

The first current-voltage conversion circuit 11 includes an operational amplifier 12 and a feedback resistor 13. The inverting input terminal of the operational amplifier 12 is connected to the first composite current output line 9, the non-inverting input terminal is connected to ground, and the feedback resistor 13 is connected between the inverting input terminal and the output terminal.

The second current-voltage conversion circuit 14 consists of an operational amplifier 15 and a feedback resistor 16, the inverting input terminal of the operational amplifier 15 is connected to the second composite current output line 10, and the non-inverting input terminal is connected to ground. The feedback resistor 16 is connected between the output terminal and the inverting input terminal.

The output terminals of the first and second current-to-voltage conversion circuits are connected to a multiplexer 19 as a combining circuit via first and second inverting amplifiers 17,18. The multiplexer 19 is controlled by the timing control circuit 6 to alternately extract the outputs of the first and second inverting amplifiers 17 , 18 and deliver the sensor output voltage V out to the common output terminal 20 .

Details of each part in FIGS. 1 and 2 are as follows.

The maximum amplitude value of the sawtooth wave generated from the first and second sawtooth wave generation circuits 4.5 is equal to the maximum amplitude value of all the first and second diodes D al -D a3 in each sensor group shown in FIG.
, Db1 to Db3 are set to a value that allows them to be turned on.

Photodiodes SO to S8, first diode D a
l to D a3, second diodes DbO to Db3, and blocking diodes DcO to Dc8 are each PI
An N-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. It is provided on an insulating substrate (not shown).

Since the photodiodes SO to S3 are connected so as to be reverse biased, they are represented by a parallel circuit of a capacitance and a current source proportional to the light intensity.

When the first diodes Dal to Da3 and the second diodes DbO to Db3 are turned on, the voltage across them, that is, the forward voltage Vf is approximately IV. First resistance Ral~
Ra3 is set at 90Ω, and the second resistor Rb1-
Rb3 is also each 90Ω. Photodiode S
The capacitance of O~S8 is about 6.5 pF, the capacitance of the first and second diodes DaL~Da3, DbO~Db3 is about 32.3 pF, and the blocking diode DcO~
The capacitance of Dc3 is approximately 0.52 pF.

[Operation] Prior to explaining the overall operation of the image sensor shown in FIG. 1, the operation of one sensor group shown in FIG. 2 will be explained with reference to FIG. 3.

When the sawtooth wave shown in FIG. 3(A) is applied to the power supply terminal 1, the first diodes D al -D a3 become conductive in sequence. As the slope voltage of the sawtooth wave gradually increases, the potential VpO at point PO gradually increases as shown in FIG. 3(B). As a result, the diode DbO is turned on, and the potential VpO at the point PO is kept at a nearly constant value (about V
f) That is, it becomes the saturation voltage value.

Note that the amplitude (slope) of the sawtooth wave in Figure 3 (A) is
The amplitude (slope) of the waveform is shown to be significantly compressed compared to that shown in Figure (B). Second diode Db of unit circuit KO
Almost simultaneously with the switching of O to the on state, the first circuit of unit circuit Kl
The diode Dal also turns on. Unit circuit K
During the period when the first diode Dal of l is non-conducting (off state), the cathode of the first diode Dal is approximately zero volts, but when the first diode Dal is on state, the slope of the sawtooth wave is further increased. As the voltage increases, the potential on the cathode side of the first diode Dal follows the ramp voltage and increases. That is, when the first diode Dal is turned on, the voltage across it is almost fixed to the forward voltage Vr, so the voltage obtained by subtracting the forward voltage vr of the diode Dal from the power supply voltage Vd is the voltage across the second resistor Rbl. Add to both ends. In addition, one second diode Dbl is added to the unit circuit.
is non-conductive, the potential at point pt is the same as that of the second resistor Rbl.
It becomes approximately equal to the voltage across both ends of . Therefore, after the first diode Dal is turned on, the potential Vpl at the point pt
gradually increases as shown in FIG. 3(B). The potential Vpl at point P1 is the forward voltage Vf of the second diode Dbl.
, it turns on and the potential Vpl at point P1
is approximately constant fi (Vf). Almost at the same time as the second diode Dbl in the unit circuit 1 turns on, the first diode Da2 in the unit circuit 2 turns on, causing a potential at point P2 as shown in FIG. 3(B). vp2 is obtained. When the slope voltage of the sawtooth wave supplied from the power supply terminal 1 further increases, the first diode Da3 of 3 in the unit circuit turns on, and the voltage at the point P3 shown in Fig. 3 (B
) is obtained. Potential VpO of points PO to P3
When ~vp3 changes sequentially as shown in FIG. 3(B), the photodiode SO connected to each point PO~P3~
S3 is sequentially driven. That is, photodiode SO
~S3 is electrically scanned. As a result, the output current ■out corresponding to the optical information is applied to the common current output line 3 as shown in Fig. 3 (
C) is obtained as shown in FIG.

When reading optical information with the photodiodes SO to S3, first the first diodes Da1 to Da3 and the second
A voltage capable of turning on all of the diodes DbO to Db3 is generated from the power supply terminal 1. Note that the first diodes Dal to Da8 and the second diode D
The voltage for turning on all of bO to Db3 can be given by the sawtooth wave shown in FIG. 3(A). In other words, the maximum value of the sawtooth wave and the voltage value in this vicinity are the first
and second diodes Dal~Da3 and DbO~Db
You can turn on all 3.

During the period when all of the first diodes Dal to Da3 and the second diodes DbO to Db3 are in the on state, the point P
Each photodiode SO to S3 is controlled by the forward voltage vr of the second diode Db port to Db3 obtained at O to P3.
is reverse biased and this capacitance is charged.

Note that since the capacitance of the photodiodes SO~S3 is extremely small, the blocking diodes DcO~D
The capacitances of the photodiodes SO to S3 can be charged by a small current in a region before the point where the forward current of c3 rises steeply.

An optical signal obtained from an object (not shown) such as a facsimile document placed opposite to the photodiodes SO to S3 in FIG.
When an optical signal is input, the amount of charge charged in the equivalent capacitance of the photodiodes SO to S8 changes depending on the presence or absence and magnitude of the optical signal.

That is, among the photodiodes SO to S3, the equivalent capacitance discharge occurs in the one to which the optical signal is input, and the equivalent capacitance discharge does not occur in the one to which the optical signal is not input. The amount of equivalent capacitance discharge changes depending on the amount of light. There are two methods for providing optical input to the photodiodes SO to S3. One method is to always provide optical input to the photodiodes SO to S3, and the other is to provide optical input only during a predetermined period (for example, a period when the sawtooth wave voltage at power supply terminal 1 is 0 volts). It is.

When the sawtooth voltage increases linearly with time as shown in FIG. 3(A), the point PO to P3 in FIG. 3(B)+:
As shown, potentials VpO1Vpl, Vp2, and Vp3 are obtained, thereby sequentially reverse biasing the photodiodes SO to S3. In other words, photodiode 5
A voltage for charging the equivalent capacitance of L-S3 is applied to photodiodes SO-S3. At this time, a charging current flows to the equivalent capacitance of the photodiodes SO to S3 that is discharged by the optical input.
Charging current does not flow to those that are not discharged because there is no optical input. The charging current of the equivalent capacitance of the photodiode SO-5S is the blocking diode D cO
−D flows to the common current output line 3 through c3. As shown in FIG. 1, the first current-voltage conversion circuit 11 or the second current-voltage conversion circuit 14 is connected between the common current output line 3 in FIG. 2 and the ground. Current 1 o
A voltage corresponding to the change in ut can be obtained.

3 and 4 show a state in which optical input is applied to all of the photodiodes SO=53 in each group B1 to B3. In this way all photodiodes 5O-53
When the photodiodes SO to S3 are sequentially driven (scanned) with the potential V pO - V p3 obtained at the points PO to P8 based on the sawtooth wave voltage after the optical input is given to ,
Photodiode 5O-531: Potential V of points PO to P3
Every time po to Vp3 rises, a charging current flows through the photodiodes SO to S3 connected thereto as shown in FIG. 3(C). That is, the potentials VpO to vp3 at each point PO to P3
As , the charging current of the equivalent capacitance of the photodiodes SO to S3 increases, and when the potentials VpO to Vp3 at each point PO to P3 are saturated, the charging current decreases.

If there is one among the photodiodes 5O-5S to which no optical input is given, no charging current will flow to it, and no current change as shown in FIG. 3(C) will occur.

Further, the amount of current change in FIG. 3(C) corresponds to the strength of optical input.

By the way, during the period Ta in which the sawtooth wave in FIG. 3(A) is generated, the output current 1 o in the positive direction shown by the arrow in FIG.
ut is flowing. In addition, the first diodes Dal to Da3
, the second diodes DbO to Db3, the blocking diodes DeO to Dc3, and the photodiodes SO to S3 are each PIN type diodes and have equivalent capacitance,
Charged when sawtooth voltage is applied. When the sawtooth voltage becomes zero, the charges of each diode are discharged, and a current flows in the common current output line 3 in the opposite direction to the normal state as shown in FIG. 3(C). The path of this reverse current includes, for example, the blocking diode Del, the photodiode Sl, the first resistor Rat, the second resistor Rbl, the first or second current-voltage conversion circuit 11.14, and the common current output line 3. Consists of. Reverse currents based on the first diodes Dal to Da3 and the second diodes DbO to Db3 similarly flow to the common current a line of force 3. This reverse current is inconvenient in combining the outputs of the sensor groups B1 to Bn.

The image sensor according to the present invention is configured to eliminate or reduce the effect of this reverse current.

Next, this operation will be explained with reference to FIGS. 1 and 4.

The first and second sawtooth wave voltages Vl and V2 shown in FIG.
The signals are distributed to odd numbered sensor groups Bl, B8...Bn-1 and even numbered sensor groups B2, B4...Bn. t in Figure 4
The first sensor group B1 is activated by the sawtooth wave in the lt3 section.
When is driven, the output voltage Va of the output stage of the first inverting amplifier 17 increases in response to the output current I out in FIG. 3(C).
After changing like the tl-t2 section in Figure 4(C),
A reverse voltage corresponding to the reverse current shown in FIG. 3(C) is generated during the period Tb from t2 to t4. However, the first sawtooth voltage V
Since l has a rest period (zero volt period) from t3 to t5 and generates the next sawtooth wave, the reading of the optical information of the third sensor group B3 is affected by the reverse voltage during the period from t2 to t4. do not. Of course, it will be a problem if the reverse voltage generation period Tb is longer than the sawtooth wave period Ta and the rest period t2 to t5, but in this embodiment, each part is adjusted so that Tb is shorter than t2 to t5. Circuit constants are set. Note that at time t4 in FIG. 4, in an image sensor that needs to discriminate the intensity of light input in N gradations (N stages),
At time t4, the difference between the amplitude value of the output voltage VaSVb at maximum optical input and the amplitude value at optical input cutoff (maximum change width 100
This is the point at which the reverse voltage value becomes smaller than the value of l/N (0 nA).

During the period when the scanning by the first sawtooth voltage vl in FIG. 4(A) is paused, the second sawtooth voltage shown in FIG. 4(B)
Scanning is performed using the sawtooth voltage v2, and a second output voltage vb shown in FIG. Obtainable.

The multiplexer 19 for output synthesis is configured to select between tl and t2 and t5 and t8 of the first output voltage Va in FIG. 4(C) and between t2 and t5 of the second output voltage vb in FIG. 4(D), respectively. t
8 to t1o section is extracted.

As a result, the combined output voltage V Out shown in FIG. 4(E) is obtained at the output terminal 20. Note that since one multiplexer discards the reverse voltage shown in FIGS. 4(C) and 4(D), the combined output voltage V out shown in FIG. 4(E) does not include the reverse voltage.

Therefore, the photodiodes 5O of each sensor group Bl-Bn
-53 a force can be obtained accurately and quickly.

[Second Example] Next, an image sensor according to a second example will be described with reference to FIGS. 5 and 6. However, in FIGS. 5 and 6, parts common to those in FIGS. 1 to 4 are designated by the same reference numerals, and their explanations will be omitted.

In this embodiment, first and second current-voltage conversion circuits 11
．． Reverse voltage absorbing diodes 21 and 22 are connected between the output terminals of the fourteen operational amplifiers 12 and 15 and the ground, respectively. Further, the output lines of the first and second current-voltage conversion circuits 11.14 are connected to a resistor 24.25 of a combining circuit 23 in place of the multiplexer 19 in FIG. The output terminals of the resistors 25 and 26 are connected in common and connected to the inverting input terminal of the operational amplifier 27.

The non-inverting input terminal of the operational amplifier 27 is connected to ground, and the feedback resistor 28 is connected between the output terminal and the inverting input terminal.

With the diode 21.22, the operational amplifier 12.1
The voltage Val shown in FIG. 6(C)(D) is applied to the output terminal of 5.
, Vbl are obtained. If the diodes 21 and 22 are not connected, voltages shown by broken lines in FIGS. 6(C) and 6(D) will occur corresponding to the reverse current in FIG. 3, but it is necessary to provide the diodes 21, 22. This is suppressed by Therefore, by adding and inverting the voltages VaL and Vbl in FIGS. 6C, 6D, and 7 in the synthesis circuit 23, the output voltage v out in FIG. 6E can be obtained. diode 21.2
2. Since the voltage component based on the reverse current has been removed, an output voltage with good continuity can be obtained just by adding.

[Third Example] Next, an image sensor according to a third example will be described with reference to FIGS. 7 and 8. However, in FIGS. 7 and 8, parts common to those in FIGS. 1 to 6 are designated by the same reference numerals, and their explanations will be omitted.

In this embodiment, the output terminal of the current-voltage conversion circuit 11.14 is connected to the input resistance 2 of the negative output inverting ideal diode 35.41.
9.36 to the inverting input terminal of operational amplifier 33.40. At this time, the output terminals of the operational amplifiers 33 and 40 have voltages Va2 and Vb shown in FIG. 8(C) and (D).
2 is obtained. If the diodes 31, 32, 38, and 39 were not present, voltages indicated by broken lines in FIGS. 6(C) and 6(D) would occur corresponding to the reverse direction current in FIG. By providing .38 and 39, this problem will no longer occur. Further, the forward current, which is a signal component, is passed through the feedback resistor 30.
37 and input resistors 29 and 36. When this voltage is synthesized by the adder circuit 42, the Vout terminal 2
0, a good output power with continuous flux as shown in FIG. 8(E) can be obtained.

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

(1) A diode can be connected between the output line of the current-voltage conversion circuit 11.14 of the image sensor in Figure 1 and the ground as in Figure 5, and reverse voltage can be absorbed in the same way. .

(2) Connecting blocking diodes DeO to DC3 in series to the first resistors Rat to Ra3 to prevent mutual interference of the photodiodes SO to S3, or connecting the blocking diodes DeO to DC3 in series to the first resistors Rat to Ra3;
can be connected between the resistors RbO to Rb3 and the first resistors Ral to Ra3.

(3) Making the sawtooth wave a step-like sawtooth wave,
and a sawtooth wave that increases in a quadratic manner.

(4) Connect the current-voltage conversion circuit to the composite current output line 9.1
It can be constructed by connecting a resistor between 0 and ground.

(5) A bias voltage source having approximately the same value as vr can be connected in series with the voltage suppression diodes 21, 22 in order to cancel out this forward voltage vr.

(6) A power source that provides a reverse bias voltage corresponding to Vf may be connected between the second diodes DbO to Db3 and the ground to widen the dynamic range.

[Effects of the Invention] As described above, according to the present invention, it is possible to eliminate or reduce the influence of voltage due to reverse current, and to read optical information from a photodiode quickly and accurately.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an image sensor according to the first embodiment of the present invention, Fig. 2 is a circuit diagram showing details of each sensor group in Fig. 1, and Fig. 3 shows the state of each part in Fig. 2. Figure 4 is a waveform diagram showing the states of each part in Figure 1, Figure 5 is a block diagram showing the image sensor of the second embodiment, and Figure 6 is a waveform diagram showing the states of each part in Figure 5. 7 is a block diagram showing a part of the image sensor of the third embodiment, and FIG. 8 is a waveform diagram showing the state of each part in FIG. 7. DESCRIPTION OF SYMBOLS 1... Power supply terminal, 4.5... First and second sawtooth wave generation circuit, 7.8... First and second multiplexer, 11.14... First and second Current-voltage conversion circuit, D al -D a3... first diode,
Db1 to Db3... second diode, Rat-R
a3...First resistor, Rb1-Rb3...Second resistor, 81-S8...Photodiode, Bl-Bn.
...Sensor group.

Claims (1)

[Claims] [1] A plurality of first diodes each having a power terminal (1) and a common terminal (2) for supplying a scanning voltage, and a first electrode and a second electrode ( Da1 to Da3) are connected in series, one end of which is connected to the power supply terminal (1), and each of the first diodes (Da1 to Da3)
Each of the first diodes (Da1 to Da3) has a directionality such that a forward current flows based on the scanning voltage.
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 power supply terminal (1); and a first resistor (Ra1 to Ra3) and a second diode (Db1 to Db3), respectively. It consists of a circuit in which the first diodes (Da1 to Da3) are connected in series.
and the common terminal (2), and the respective second diodes (Db1
~Db3) flows through each second diode (Db1) based on the scanning voltage.
-Db3) have a plurality of second series circuits, and a plurality of second series circuits each connected between the second electrode of each first diode (Da1 to Da3) and the common terminal (2). the second resistors (Rb1 to Rb3), the common current output line (3), and the connection points (P1 to P3) between the first resistors (Ra1 to Ra3) and the second diodes (Db1 to Db3); ) and the common current output line (3), a plurality of photodiodes (S1 to S3) each connected with reverse bias directionality, and the plurality of photodiodes (S1 to S3) In an image sensor that forms a plurality of sensor groups each including blocking diodes (Dc1 to Dc3) connected to each other to separate each other from each other, and drives the sensor groups in a time-division manner, the sensor common current output line (
3) is provided for each even-numbered sensor group and odd-numbered sensor group, and after signal processing is performed for each common current output line, the signals are combined, and the output signals of the sensor groups can be continuously extracted. [2] The image sensor according to claim 1, wherein the image sensor has two scan voltage generation circuits, one for scanning the odd-numbered sensor groups and the other for scanning the even-numbered sensor groups, and each scanning voltage generation circuit has one scanning voltage generation circuit. The constant voltage generating circuit and the sensor group are configured to repeatedly generate a scanning voltage with a time difference required to scan the two sensor groups, and to generate the scanning voltage alternately at even numbered positions. An image characterized in that a switching element is provided between the sensor groups, the switching element is switched at the timing when each of the sensor groups is scanned, and a scanning voltage is sequentially applied to the even-numbered sensor group and the odd-numbered sensor group to scan each sensor group. sensor.