JPH0566061B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a scanning circuit device for sequentially supplying voltage to a plurality of circuit elements, and more particularly, to a scanning circuit suitable for a one-dimensional image sensor. Regarding equipment.

[Prior art and problems to be solved by the invention] An image sensor includes a plurality of photoelectric conversion elements for exchanging optical information into electrical signals, and selects an electrical signal by electrically scanning the plurality of photoelectric conversion elements. 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 image sensor having an integrated circuit configuration, the width of one photoelectric conversion element, that is, one pixel (for example, 125 micrometers)
one field effect transistor must be placed. 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.
The yield of image sensor manufacturing has become low. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a scanning circuit device using a diode having fewer electrodes than a transistor.

[Means for Solving the Problems] To achieve the above object, the present invention will be described with reference to the reference numerals in the drawings showing the embodiments. and a second electrode.
A circuit in which Da1 to Da3 are connected in series, one end of which is connected to the voltage source 1, and each diode has a directionality such that the forward current of each diode Da1 to Da3 flows based on the sawtooth wave. A first series circuit that diodes Da1 to Da3 have and in which the first electrode of each of the diodes Da1 to Da3 is arranged on the side of the voltage source 1, and a diode C1 each functioning as a capacitor or a capacitor. ~C3 or Dc1~Dc
3 and first resistors Ra1 to Ra3 are connected in series, and the respective diodes Da1 to Da
a plurality of second series circuits connected between the second electrodes of the respective diodes Da1 to Da3 and the other end of the voltage source 1; a plurality of second resistors Rb1 to Rb3 each connected between the other ends thereof, and a plurality of scanned circuit elements S1 each connected substantially in parallel to each of the first resistors Ra1 to Ra3; This relates to a scanning circuit device consisting of .about.S3.

[Function] The diodes Da1 to Da3 in the present invention function as switches for sequentially driving the circuit elements S1 to S3 to be scanned, and are made sequentially conductive by a sawtooth voltage, that is, a ramp voltage. As a result, the first
A voltage is also sequentially obtained across the resistors Ra1 to Ra3, and this voltage is applied to the circuit elements S1 to S3 to be scanned. This circuit does not include transistors and is therefore easy to manufacture.

[Embodiment] Next, a one-dimensional image sensor according to an embodiment of the present invention will be described with reference to FIGS. 1 to 5.

The one-dimensional image sensor shown in FIG.
2. K3, load circuit RL, and coupling capacitor C
and an output terminal 2. This one-dimensional image sensor is configured to be able to detect more than three pixels. However, since it is difficult to show the entire configuration of this one-dimensional image sensor in the drawing, only a part of it is shown in FIG.

Three mutually identical unit circuits K1, K2, K3
are diodes Da1, Da2, Da3, capacitors C1, C2, C3, and first resistors Ra1, Ra
2, Ra3, second resistors Rb1, Rb2, Rb3,
Three diodes Da1, Da2, Da3 each having an anode (first electrode) and a cathode (second electrode) consisting of photoelectric conversion elements S1, S2, S3 and blocking diodes Db1, Db2, Db3 are connected to each other. One end (left end) of the series-connected circuit (first series circuit) is connected to one end of the voltage source 1. The diodes Da1, Da2, and Da3 have directionality that is biased in the forward direction by the voltage of the voltage source 1. That is, the anodes (first electrodes) of the 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 diodes Da1 to Da3 are arranged on the voltage source 1 side.

Capacitors C1 to C3 and first resistors Ra1 to
A circuit (second series circuit) in which each of Ra3 is connected in series is connected to each other.

Photoelectric conversion elements S are connected to interconnection points P1, P2, and P3 between capacitors C1 to C3 and first resistors Ra1, Ra2, and Ra3 in each unit circuit K1, K2, and K3.
The cathodes of 1, S2, and S3 are connected to each other. The anodes of the photoelectric conversion elements S1, S2, and S3 are connected to the other end (ground) of the voltage source 1 via blocking diodes Db1 to Db3 and a common load resistance RL for preventing mutual interference of the photoelectric conversion elements S1 to S3. It is connected to the. Therefore, each of the photoelectric conversion elements S1 to S3 is substantially connected in parallel to each of the first resistors Ra1 to Ra3. Photoelectric conversion element S1, S
2 and S3 consist of photodiodes, which are connected so as to be reverse biased by the voltage of the voltage source 1.
Therefore, the current flowing through the photoelectric conversion elements S1 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. 2 is set to a value that can turn on all the diodes Da1 to Da3 in FIG. 1. Further, the slope of the ramp voltage is determined to be a gentle slope that does not overlap the operations of the unit circuits K1 to K3.

Photoelectric conversion elements S1 to S3, diodes Da1 to
Da3, blocking diodes Db1 to Db3 are
Each is a pin junction diode, and consists 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. is provided on an insulating substrate (not shown).

Since the photoelectric conversion elements S1 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 photoelectric conversion elements S1 to S3 is extremely small.

When the diodes Da1 to Da3 and Db1 to Db3 are turned on, the voltage across them, that is, the forward voltage Vf, is approximately 1V. The first resistors Ra1 to Ra3 are each 3 kΩ, and the second resistors Rb1 to Rb3 are each 10 kΩ, and these are made of TiO ₂ , Ta-SiO ₂ or
It is made of a material such as NiCr. Further, the capacitance of the capacitors C0 to C3 is 100 pF.

[Operation] Now, the voltage of voltage source 1 is Vd, and the diode Da1~
The potential of the cathode of Da3 is V1~V3, the voltage across the capacitors C1~C3 is Vc1~Vc3, P1~
If the potential at point P3, that is, the voltage across the first resistors Ra1 to Ra3, is Vp1 to Vp3, the state of each part is the fourth
Changes as shown in the figure. That is, sawtooth voltage
When the first stage diode Da1 is turned on due to an increase in Vd, its cathode potential changes as shown by V1. Furthermore, since the charging current of the capacitor C1 flows non-linearly during the period when the cathode potential V1 of the diode Da1 is low, the voltage Vp1 of the first resistor Ra1
increases following the increase in cathode potential V1.
However, when the voltage Vc1 of the capacitor C1 increases in proportion to the cathode potential V1 at the same speed, the voltage Vp1 of the first resistor Ra1 becomes saturated. That is, when the capacitor C1 is charged with a constant current, the voltage Vp1 of the resistor Ra1 becomes constant.

Next, capacitor C1 and resistor of unit circuit K1
Using a series circuit with Ra1 as an example, changes in the voltage Vc1 of the capacitor C1 and the voltage VR1 of the resistor Ra1 will be explained in detail. The ramp (slope) coefficient of the sawtooth voltage Vd is a, the voltage across resistor Rb1 is V1=at,
The values of capacitor C1 and resistor Ra1 are C1, R1,
If time is t, Vc1 and VR1 can be expressed by the following equations.

Vc1=at-aC1R1 (1-e ^-t/C1R1 ) VR1=aC1R1 (1-e ^-t/C1R1 ) Since Vc1 and VR1 have a relationship of at-Vc1=VR1, first we will explain the change in Vc1. ,
Initially, no charge is accumulated in C1, and the voltage V
1 is also 0 [V], so Vc1 and Vr1 are 0 [V]
It is. As V1 increases linearly, C1 and
Current begins to flow in the Ra1 circuit. This current causes a voltage drop VR1 in Ra1. Charge Q1 begins to accumulate in C1, and Vc1 is generated. VR1 and
Vc1 gradually increases.

However, immediately after V1 starts to rise, the absolute value of V1 is small, so the current is very small, and charge Q1 accumulates in C1 very slowly. Therefore, since Vc1 rises at a much slower rate than the rising speed of V1, Vc1 is a value that can be considered almost zero, and VR1=V1, and VR1 is
It rises at about the same speed as the input voltage V1.

As time passes, V1 increases and the current also increases. At the same time, charge Q1 is stored in C1. As the current increases, the rate at which the charge Q1 increases also increases. In other words, Vc1 increases exponentially.

When Vc1 increases, the voltage Vr1 applied to Ra1
It can no longer be said that Vr1=V1, and more precisely,
VR1=V1-Vc1. VR1 and Vc1 increase with time. Vc1 increases forever as V1 increases, but VR1 saturates without exceeding a certain value. At that time, the current also becomes a constant value, and charge Q1 accumulates in C1 at a constant speed.
Vc1 increases at a constant rate. This rising speed is equal to the rising speed of the input voltage V1.

The cathode potential of the first stage diode Da1 is the second
When the level that turns on the diode Da2 in the second stage is reached, the same operation as in the previous stage is repeated in the second stage unit circuit K2.

When the potentials Vp1 to Vp3 at points P1 to P3 change sequentially as shown in FIG. Driven sequentially.
That is, the photoelectric conversion elements S1 to S3 are electrically scanned.

In the circuit of FIG. 1, photoelectric conversion elements S1 to S3
are arranged one-dimensionally. When reading optical information with these photoelectric conversion elements S1 to S3, first, the voltage source 1 is set to a voltage that can turn on all of the diodes Da1 to Da3 and saturate all the potentials of P1 to P3. Generate from. Note that the voltage for turning on all of the diodes Da1 to Da3 and bringing all the potentials at points P1 to P3 into a saturated state can be applied in the form of a sawtooth wave as shown in FIG. In other words, the maximum value of the sawtooth wave and the voltage value in the vicinity are the diode Da1
It is possible to turn on all of ~Da3 and saturate all potentials of points P1 to P3.

All diodes Da1 to Da3 are on,
In addition, during a period when all the potentials at points P1 to P3 are saturated, each photoelectric conversion element S1 to S3 is reverse biased by the potentials Vp1 to Vp3 at points P1 to P3,
A capacitance Cs, equivalently shown in FIG. 3, is charged. In addition, since the equivalent capacitance Cs is extremely small, the blocking diodes Db1 to Db
Charging of this equivalent capacitance Cs can be achieved by the current in the region before the point where the forward current of 3 suddenly rises.

An optical signal obtained from an object (not shown), such as a facsimile document, placed opposite to the image sensor in FIG.
When input to S3, the amount of charge charged in the equivalent capacitance Cs of the photoelectric conversion elements S1 to S3 changes depending on the presence or absence and magnitude of the optical signal. That is, among the photoelectric conversion elements S1 to S3, a 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 signals to the photoelectric conversion elements S1 to S3. One is a method of constantly providing optical signals to the photoelectric conversion elements S1 to S3, and the other is a method of providing optical input only during a predetermined period (for example, a period when the voltage Vd of voltage source 1 is 0 volts). It is.

When the voltage Vd of the voltage source 1 increases linearly with time as shown in FIG. 4A, potentials Vp1, Vp2, Vp3 are obtained at points P0 to P3 as shown in FIG. 4A, and thereby Photoelectric conversion elements S1 to S3 are sequentially reverse biased. In other words, a voltage for charging the equivalent capacitance Cs shown in FIG. 3 is applied to the photoelectric conversion elements S1 to S3. At this time, a charging current flows to those of the equivalent capacitance Cs of the photoelectric conversion elements S1 to S3 that are discharged due to optical input, but a charging current flows to those that are not discharged due to no optical input. do not have. Since the charging current of the equivalent capacitance Cs of the photoelectric conversion elements S1 to S3 flows through the blocking diodes Db1 to Db3 and the load resistor RL, the voltage of the load resistor RL changes depending on the presence or absence of the charging current, and at the same time the voltage is output. The voltage Vout at terminal 2 also changes. Further, the level differs between when scanning starts and after that. For this reason,
The voltage across the load resistor RL also increases as the ramp voltage increases. However, the load resistance due to the coupling capacitor C
If the AC component of the voltage of RL is extracted, the output voltage Vout corresponding to the optical input of the photoelectric conversion elements S1 to S3 can be obtained.
can be obtained. FIG. 4B shows the output when optical input is applied to two photoelectric conversion elements S1 and S2, but no optical input is applied to one photoelectric conversion element S3. In this case, photoelectric exchange elements S1, S2, S
3 are sequentially scanned, a charging current flows during the scanning of S1 and S2, but no charging current flows during the scanning of S3. As a result, photoelectric conversion elements S1 to
Spatial optical information in S3 is converted into voltage changes on the time axis.

As described above, in this embodiment, the photoelectric conversion elements S1 to
Sequential driving (scanning) of S3 can be performed by a diode without using a transistor. Diodes are easier to manufacture than field-effect transistors because they do not require a gate electrode. For example, bit interval
In the case of 125 μm, it becomes possible to increase the width of the wiring conductor to 20 μm or more, significantly improving manufacturing yield. Note that when the switch element is composed of a field effect transistor, the width of the wiring conductor should be approximately
It was necessary to make it 10 μm.

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

(1) Blocking diode Db shown in Figure 1
1 to Db3 can be omitted. in this case,
The photoelectric conversion elements S1 to S3 are photoconductive elements.

(2) The charging currents of the photoelectric conversion elements S1 to S3 can also be read using the circuit shown in FIG. In the circuit shown in FIG. 5, a capacitor CL is connected to the position of the load resistor RL shown in FIG. Therefore,
The charging current of the photoelectric conversion elements S1 to S3 in FIG. 1 flows through this capacitor CL. As a result, the capacitor CL is connected to the photoelectric conversion elements S1 to S1.
The charging state corresponds to the charging current of No. 3. A switch 3 connected in parallel to the capacitor CL is periodically turned on in synchronization with the scanning of the photoelectric conversion elements S1 to S3. This allows the capacitor to
CL is periodically brought into a discharge state, and voltages corresponding to the charging currents of the plurality of photoelectric conversion elements S1 to S3 are sequentially obtained from the capacitor CL. The voltage on the capacitor CL is sent to the output terminal 2 via the operational amplifier 4.

(3) A sample hold circuit or a peak hold circuit can be connected to the output terminal 2 in FIGS. 1 and 5.

(4) A signal for periodically controlling the sample-hold circuit or the peak-hold circuit connected to the switch 3 and/or the output terminal 2 in FIG. 5 can be generated based on the clock. It is also possible to generate this periodic control signal based on the current change time of the voltage source 1, or to generate the periodic control signal based on the current change time of the voltage source 1, or to
The lower ends of 3 are connected in common, and the lower ends of the voltage source 1 are connected between this common connection point and the lower end (ground) of the voltage source 1. The lower ends of Rb3 are connected in common, and it can be made based on the change point in the output current of a current detector connected between this common connection point and ground.

(5) The sawtooth wave generated from the voltage source 1 may change like a quadratic curve with time, as shown in FIG.

(6) If the number of read pixels of the image sensor according to the embodiment is increased, the driving voltage Vd must be increased accordingly. Therefore, it is desirable to set the maximum number of read pixels to about several dozen. When increasing the number of pixels, the image sensor may be divided into a plurality of blocks and driven.

In FIG. 7, n unit circuits corresponding to unit circuits K1 to K3 in FIG. 1 are connected to m circuit blocks B.
It is divided into 1 to B2...Bm. Each circuit block B1 to Bm includes a unit circuit K1 shown in FIG.
.about.K3, and corresponds to the image sensor circuit shown in FIG. 1 except that the voltage source 1 is omitted. Each circuit block B1 to Bm has a voltage source 1a connected to a multiplexer 10.
connected via. Each circuit block B1
The output terminals of ~Bm are commonly connected via amplifiers A1~Am. The voltage source 1a is shown in FIG. 8A.
The sawtooth wave (triangular liquid) shown in is generated repeatedly. Multiplexer 10 distributes the sawtooth wave of FIG. 8A to circuit blocks B1-Bm, as shown in FIGS. 8B and 8C. Each circuit block B1~
The optical input to each photoelectric conversion element of Bm is always given as shown in FIG. 8D.

9 and 10 show another method of driving the image sensor. In FIG. 9, just as in FIG. 7, n unit circuits corresponding to the unit circuits K1 to K3 in FIG. 1 are connected to m circuit blocks B.
It is divided into 1 to Bm. Each circuit block B
1 to Bm are connected to the voltage source 1, respectively. The voltage source 1 of FIG. 9 generates the sawtooth wave shown in FIG. 10A, similar to that of FIG. 1. The sawtooth waves are simultaneously supplied to circuit blocks B1-Bm as shown in FIGS. 10B and 10C. As a result, scanning starts at the same time in each of the circuit blocks B1 to Bm, and outputs are generated at the same time. The output of each circuit block B1-Bm is sent to a signal processing circuit 11 including a memory. The signal processing circuit 11 converts the outputs of circuit blocks B1 to Bm into circuit blocks B1 to Bm.
Place them on a common time axis to correspond to the arrangement order of Bm. In the image sensor of FIG. 9, optical input to the photoelectric conversion element is applied during a period when the drive voltage Vd is zero, as shown in FIG. 10D.

(7) A voltage may be applied to the cathode terminals of the diodes Db1 to Db3. That is, the ground can be set to any voltage without setting it to zero volts.

(8) As shown in FIG. 11, in place of the capacitors C1 to C3 in FIG. 1, diodes Dc1 to Dc3 functioning as equivalent capacitors may be connected in the opposite direction. The capacitances of the diodes Dc1 to Dc3 are made larger than the capacitances of the photoelectric conversion elements S1 to S3.

[Effects of the Invention] As described above, according to the present invention, a scanning device using a diode and having a simple configuration can be provided.

[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 of the voltage supplied from the voltage source in FIG. 1, FIG. 3 is an equivalent circuit diagram of a photoelectric conversion element, and FIG. The figure is a waveform diagram showing voltages at various parts in Figure 1, Figure 5 is a circuit diagram showing a modification of the output circuit of the photoelectric conversion element, Figure 6 is a waveform diagram showing a modification of the sawtooth wave, and Figure 7 is a waveform diagram showing a modification of the output circuit of the photoelectric conversion element. A block diagram showing the principle of the driving method of a photoelectric conversion element when there are many unit circuits,
FIG. 8 is a diagram showing the state of each part in FIG. 7, FIG. 9 is a block diagram showing the principle of the driving method of the photoelectric conversion element when there are many unit circuits, similar to FIG. 7, and FIG.
0 is a diagram showing the state of each part in FIG. 9, and FIG. 11 is a circuit diagram showing a modified example of the image sensor. 1... Voltage source, 2... Output terminal, Da1 to Da3
...Diode, C1-C3...Capacitor,
Ra1 to Ra3...first resistance, Rb1 to Rb3...
Second resistor, S1...S3...photoelectric conversion element.

Claims (1)

[Claims] 1. A circuit in which a voltage source 1 for supplying a sawtooth wave and a plurality of diodes Da1 to Da3 each having a first electrode and a second electrode are connected in series. One end is connected to the voltage source 1, and each of the diodes Da1 to Da3 has a directionality such that the forward current of each of the diodes Da1 to Da3 flows based on the sawtooth wave, and each of the diodes Da1 to a first series circuit in which the first electrode of Da3 is placed on the side of the voltage source 1; diodes C1 to C3 or Dc1 to Dc3 each functioning as a capacitor or a capacitor; and first resistors Ra1 to Ra3; a plurality of second series circuits each connected between the second electrode of each of the diodes Da1 to Da3 and the other end of the voltage source 1; The second of the diodes Da1 to Da3
a plurality of second resistors Rb1 to Rb3 each connected between the electrode of the voltage source 1 and the other end of the voltage source 1; and a plurality of second resistors Rb1 to Rb3 each connected substantially in parallel to each of the first resistors Ra1 to Ra3. A scanning circuit device comprising circuit elements S1 to S3 to be scanned.