JPH0530278A - Picture reader, line image sensor and shift register - Google Patents

Abstract

PURPOSE:To provide the circuit with high reliability whose fluctuation of a threshold voltage is suppressed, the line image sensor, the picture reader and their operating method. CONSTITUTION:The line image sensor and the picture reader are formed, which consist of the circuit that an inverter comprises a load resistor R1 and a drive transistor(TR) D1 and a path TR P1 and a control resistor RC1 having a larger resistance are connected to the input of the inverter. The threshold voltage of the TRs is recovered at the pause of the circuit by setting a prescribed voltage to the control resistor, power, input, clock and ground lines and applying a negative voltage to the gates of the drive TR D1 and the path TR P1.

Description

Detailed Description of the Invention

[0001]

The present invention relates to amorphous silicon (hereinafter a)
-Si) and a thin film transistor made of polycrystalline silicon (hereinafter abbreviated as p-Si) formed by a laser annealing method, a dynamic shift register including a circuit added with a function of correcting fluctuations in threshold voltage of a thin film transistor and recovering characteristics.
The present invention relates to a static shift register, a line image sensor and an image reading device using these shift registers.

[0002]

2. Description of the Related Art Thin film transistors having threshold voltage fluctuations are used in dynamic circuits and static circuits including logic circuits used in line image sensors for image reading devices.

As a logic circuit using an a-Si thin film transistor, for example, there is a shift register circuit described in JP-A-61-15363. As in this prior art, an inverter is a basic element in a logic circuit, and the inverter is combined in multiple stages to form a shift register.
The output of each inverter becomes the input of the next-stage inverter.
Since the output voltage of the inverter is in the range of the power supply voltage, the input voltage of the inverter is always 0V or higher.

An image sensor using an a-Si thin film transistor is manufactured by Nikkei Electronics
o. 434 (November 16, 1987), pages 207-221. In this prior art, the a-Si thin film transistor is used as a switch and does not include a logic circuit.

In a liquid crystal display using an a-Si thin film transistor, the a-Si thin film transistor is used as a switch in addition to being used as a switch. The 6th display about this conventional technology
Research Conference, Japan Display ''
86 Proceedings (1986), pages 212-215.

[0006]

Although an a-Si thin film transistor and a p-Si thin film transistor can form an enhancement-type field effect transistor, a threshold voltage drift called a threshold voltage drift caused by a physical property of a material which depends on a material and a manufacturing process. Has a change phenomenon.

That is, when the gate-source voltage is applied, the threshold voltage fluctuates to be positive at a positive gate-source voltage and to be negative at a negative voltage. Therefore, in a logic circuit to which a gate-source voltage of 0 V or more is constantly applied, the threshold voltage of the a-Si thin film transistor may drift positively, and if the circuit operation is performed for a long time, the drift may become large and may eventually stop operating.

By improving the material, the drift of the threshold voltage can be reduced to some extent, but the instability of the physical properties of the amorphous silicon forming the circuit and the instability of the interface between the gate insulating film capable of forming a channel and a-Si. However, it is difficult to eliminate it fundamentally. Therefore, it is necessary to devise to reduce the threshold voltage drift on the circuit.

The prior art described above does not consider the point of preventing the threshold voltage drift in the circuit when it is used in a logic circuit except when the a-Si thin film transistor is used as a switch. There is a problem in that the threshold voltage fluctuates and the circuit does not work. As a result, the line image sensor using the transistor and the image reading device equipped with the line image sensor may be defective.

The present invention relates to an a-Si thin film transistor and a p-type thin film transistor.
A shift register for reducing the threshold voltage drift of a circuit using a Si thin film transistor to improve the reliability of long-term circuit operation, and a highly reliable and miniaturizable line image sensor using the shift register, and An object of the present invention is to provide an image reading device using this line image sensor and a method of operating these shift register, line image sensor, and image reading device.

[0011]

In order to solve the above-mentioned problems, the inventor performs drift correction of the threshold voltage of the thin film transistor in an operation idle period of a circuit including the thin film transistor, thereby stabilizing the threshold voltage and making the circuit stable. Of the present invention, it is possible to improve the reliability of long-term operation, and a shift register to which a threshold voltage drift correction means of the thin film transistor of the present invention is added, a line image sensor using this shift register, and an image using this line image sensor. The reader and the method of operating them have been invented.

The image reading apparatus has the following means.

The image reading device includes a photoelectric conversion element, a shift register, a buffer, a transfer switch, etc., and a line image sensor for transferring the photoelectric conversion output of the photoelectric conversion element to an external circuit is housed in a casing together with a control system. For those configured with a transistor having a threshold voltage fluctuation, a power supply drive circuit that changes the power supply voltage when the line image sensor is operating and when the line image sensor is inactive, and the operating time of the line image sensor is detected and detected. Means for storing and means for generating a threshold voltage recovery signal of the transistor corresponding to the operating time of the line image sensor when the reading of the original is suspended.

The image reading device includes a plurality of circuits each including an inverter including a load resistance, a drive transistor formed of a transistor having a threshold voltage fluctuation connected to the load resistance, and a pass transistor connected to an input of the inverter. For a line image sensor that is equipped in series with a control system and is housed in a housing, the control line is connected to the input of the inverter via a control resistor with a resistance value larger than the load resistance. Connect different power supply lines to the inverters of the odd-numbered circuit and the inverters of the even-numbered circuit of the continuous circuit, connect the ground line to the inverter, and connect the pass transistor of the odd-numbered circuit and the even-positioned circuit. Means are provided for connecting different clock lines to the gates of the pass transistors of the circuit.

A line image in which the image reading apparatus is provided with a plurality of circuits, each of which has an inverter formed of a load transistor and a drive transistor, which are transistors having threshold voltage fluctuations, and a pass transistor connected to the input of the inverter. For the sensor that is configured by housing the sensor together with the control system in the case, connect the control line to the input and output of the inverter through the control resistor that has a resistance value larger than the on resistance of the load transistor. , Connect different power lines to the gate and drain of the load transistor of the inverter, connect the ground line to the source of the drive transistor, and connect the pass transistor of the odd-numbered circuit and the pass transistor of the even-numbered circuit in the continuous circuit. Means are provided for connecting different clock lines to the gates.

As an operation method of the image reading apparatus, when the shift register constituting the line image sensor used in the image reading apparatus is in operation, a power supply voltage is applied to the power supply line and a ground voltage is applied to the ground line to operate the shift register. The voltage is applied to the power supply line, the ground line, and the control line so that a negative voltage is applied to the gate and the source of the transistor having a threshold voltage fluctuation that constitutes the shift register during the rest period.

Further, a plurality of circuits each including a load resistance, an inverter composed of a drive transistor composed of a transistor having a threshold voltage fluctuation connected to the load resistance, and a pass transistor connected to an input of the inverter are connected in series. As an operation method of an image reading apparatus equipped with a line image sensor, the power resistance lines are connected to the load resistances of the odd-numbered circuits and the even-numbered circuits of a plurality of continuous circuits, and the ground line is connected to the source of the drive transistor. The power supply voltage is applied to multiple power supply lines and the ground voltage is applied to the ground line when the circuit of the line image sensor that connects the circuit is connected, and the gates of the transistors that form the circuit are connected to the multiple power supply lines and ground lines when the circuit operation is suspended. Apply a voltage in a sequence that applies a negative voltage to the source and gate / drain Than it is.

A control system for a line image sensor in which a plurality of circuits each including an inverter composed of a load transistor and a driving transistor composed of transistors having threshold voltage fluctuations and a pass transistor connected to the input of the inverter are continuously formed As an operation method of the image reading device housed in the housing, different power supply lines are connected to the gates and drains of load transistors of a plurality of continuous circuits, and a ground line is connected to the source of the drive transistor.
When the circuit is operating, the power supply voltage is applied to different power supply lines, the ground voltage is applied to the ground line, and when the circuit is at rest, multiple power supply lines and ground lines are negatively connected to the gate / source and gate / drain of the transistors that make up the circuit. The voltage is applied in a sequence in which the voltage is applied.

For the line image sensor, the line image sensor is composed of a load resistance, an inverter composed of a driving transistor composed of a transistor having a threshold voltage fluctuation connected to the load resistance, and a path connected to the input of the inverter. In the case of a shift register including a plurality of circuits each including a transistor, the control line is connected to the input of the inverter via a control resistor having a resistance value larger than that of the load resistor, Different power supply lines are connected to the inverters of the odd-numbered circuit and the inverters of the even-numbered circuit of a plurality of continuous circuits, the ground line is connected to each of the inverters, and the pass transistor of the odd-numbered circuit and the even-numbered circuit are connected. Means for connecting different clock lines to the gates of the pass transistors.

In addition, the line image sensor is provided with a plurality of circuits, each of which includes an inverter including a load transistor and a driving transistor, which are transistors having threshold voltage fluctuations, and a pass transistor connected to the input of the inverter. In the case of a shift register consisting of a shift register, a control line is connected to the input and output of the inverter through a control resistor having a resistance value larger than the on resistance of the load transistor, and the gate and drain of the load transistor of the inverter are connected. Connect different power lines to
A means for connecting the ground line to the source of the drive transistor and connecting different clock lines to the gates of the pass transistors of the odd-numbered circuits and the pass transistors of the even-numbered circuits of the plurality of continuous circuits are provided.

Further, for the line image sensor which is composed of a shift register composed of a transistor having a threshold voltage fluctuation, a power supply drive circuit for changing the power supply voltage when the line image sensor is in operation and at rest is provided.

As a method of operating the line image sensor, for a line image sensor having a shift register in which a plurality of circuits each having an inverter using a transistor having a threshold voltage fluctuation are connected, The changed threshold voltage of the transistor is applied to the gate-source and gate-drain with a voltage of the opposite polarity to the changed polarity of the threshold voltage during the idle period of the shift register, or the changed threshold voltage of the transistor is changed. A voltage having a polarity opposite to the polarity in which the threshold voltage of the transistor fluctuates according to the time when the positive voltage is applied to the gate-source voltage is applied to the gate-source and the gate-drain during the idle period of the shift register.

With respect to the shift register, the shift register includes an inverter composed of a load resistance, a drive transistor composed of a transistor having a threshold voltage fluctuation connected to the load resistance, and a pass transistor connected to the input of the inverter. For those that are configured by including a plurality of circuits provided in series, connect the control line to the input of the inverter through a control resistor having a resistance value larger than the load resistance, and Connect different power supply lines to the odd-position circuit inverter and even-position circuit inverter, connect the ground line to the inverter, and use different clock lines for the gates of the odd-position circuit pass transistor and the even-position circuit pass transistor. And means for connecting.

Further, the circuit is continuously provided with a plurality of circuits each having an inverter composed of a load transistor and a driving transistor which are composed of a transistor having a threshold voltage fluctuation, and a pass transistor connected to the input of the inverter. For those that are connected, connect a control line to the input and output of the inverter through a control resistor having a resistance value larger than the on resistance of the load transistor, and connect different power supply lines to the gate and drain of the load transistor of the inverter. And a means for connecting a ground line to the source of the drive transistor and connecting different clock lines to the gates of the pass transistors of the odd-numbered circuits and the pass transistors of the even-numbered circuits of the plurality of continuous circuits.

As a method of operating the shift register, a power supply voltage is applied to the power supply line during operation, a ground voltage is applied to the ground line, and a negative voltage is applied to the gate / source of the transistor having threshold voltage fluctuations which constitutes the shift register during operation suspension. The voltage is applied to the power supply line, the ground line, and the control line in the same manner as the above voltage.

Further, a plurality of circuits, each of which is composed of a load resistance, an inverter composed of a drive transistor composed of a transistor having a threshold voltage fluctuation connected to the load resistance, and a pass transistor connected to the input of the inverter, are connected in series. For a shift register equipped with a control line, connect the control line to the input of the inverter through a control resistor that has a resistance value greater than the load resistance, and load the odd-numbered circuit and the even-numbered circuit in the continuous circuit. Connect different power supply lines to the resistance, connect the ground line to the inverter, apply power supply voltage to multiple power supply lines when the shift register is operating, add ground voltage to the ground line, and use multiple power supply lines when the shift register is idle. Apply a negative voltage to the ground line on the gate / source and gate / drain of the transistors that make up the shift register. It is intended to apply a voltage in sequence as obtain.

Further, for a shift register having a plurality of circuits, each of which is composed of a load transistor and a drive transistor, which are transistors having threshold voltage fluctuations, and a pass transistor, which is connected to the input of the inverter, in series, , Connect different power supply lines to the gates and drains of the load transistors of a series of circuits, connect the ground line to the source of the drive transistor, apply the power supply voltage to the different power lines when the shift register operates, and connect the ground line to the ground. A voltage is applied to the plurality of power supply lines and ground lines when the shift register is at rest, and a negative voltage is applied to the gate / source and gate / drain of the transistors forming the circuit.

In addition, the threshold voltage of the transistor which fluctuates during the operation period of the shift register is applied to the gate / source and the gate / drain with a voltage having the opposite polarity to the fluctuating polarity of the threshold voltage during the idle period of the shift register, or Alternatively, a voltage having a polarity opposite to the polarity in which the threshold voltage of the transistor fluctuates according to the time when a positive voltage is applied to the gate-source voltage of the transistor fluctuated during the operation period of the shift register is applied to the gate source and the gate drain. It is added to the operation pause period.

The transistors having threshold voltage fluctuations used in each of the above means are amorphous silicon transistors or polycrystalline silicon transistors.

Further, the control resistor used in the shift register, the line image sensor and the image reading device is a load resistor,
Alternatively, it is provided with a means for making the resistance value 10 times or more larger than the ON resistance of the load transistor.

[0031]

[Function] In a dynamic circuit or a static circuit including a conventional logic circuit, the potentials of the power supply and the ground are constant,
It is customary to assume a state of constant operation. But,
A line image sensor used in an image reading device such as a facsimile machine, a copying machine, or an image scanner does not always operate. Even when the line image sensor normally operates, the operation time is short, and the idle time is Is longer.

The basic operation of the present invention is to suspend the threshold voltage of a transistor having a threshold voltage fluctuation such as an a-Si thin film transistor or a p-Si thin film transistor which fluctuates during a predetermined circuit operation. Shift register and line equipped with such a circuit by changing the power supply voltage and other input voltage from the state in which the circuit is operating in an appropriate sequence during the period when the circuit is operating. The long-term reliability of an image sensor and an image reading apparatus using this line image sensor is ensured.

The operation will be described below centering on the important circuit configuration and circuit operating method as means for solving the above problems.

Load resistance and a- connected to this load resistance
The inverter composed of a Si thin film transistor (abbreviated as “E / R inverter”) has a logic 0, 1 which is the reverse of the input voltage of VH, VL corresponding to the input of the inverter 1, 0.
The voltages of VL and VH corresponding to are output. The pass transistor composed of an a-Si thin film transistor connected to the input of this inverter has a function as a switch for controlling conduction and non-conduction of an input signal. A dynamic logic circuit or a static logic circuit can be configured by combining the basic elements of the inverter and the pass transistor.

A clock for determining the timing of the dynamic operation is normally connected to the gate of the pass transistor. Since this clock is supplied from an external circuit, the gate of the pass transistor can directly control the voltage from the external circuit. Therefore, a negative voltage can be externally applied to the gate of the pass transistor.

On the other hand, since the input voltage of the inverter is basically the output voltage of the preceding inverter, a positive gate-source voltage is usually added. By connecting the control input to the input of this inverter through a resistor and setting the power supply voltage to an appropriate value, it is possible to apply a negative voltage to the gate of the a-Si thin film transistor rather than the source and drain.

Since the control resistance connected to the input of the inverter is sufficiently larger than the resistance value of the load resistance of the inverter, the output of the inverter in the previous stage fills the input of the inverter in the next stage through the pass transistor during normal circuit operation. When discharged, the control inputs will not participate in circuit operation. On the other hand, in the voltage holding state where the input of the inverter is cut off from the output of the preceding inverter or the like with the pass transistor being cut off, the input of the inverter is gradually charged and discharged by the control input via the control resistor.

The charging / discharging time constant is sufficiently longer than the operating time of the dynamic logic circuit. Therefore, the input of the inverter becomes a voltage determined by the output of the preceding-stage inverter when the dynamic logic operation is performed, and becomes the voltage determined by the control input when the dynamic logic operation is not performed for a long time. This control input can be a voltage more negative than the source and drain voltages so that a negative voltage can be applied to the gate of the drive transistor of the inverter when the circuit is idle.

The fluctuation of the threshold voltage of the a-Si thin film transistor or the p-Si thin film transistor normally changes to positive when the gate-source voltage is positive, and changes to negative when the gate-source voltage is negative.
Therefore, the threshold voltage that fluctuates positively when the dynamic logic circuit is operating is negatively fluctuated by applying a negative voltage to the gate and source using the control input when the dynamic logic circuit is inactive, and as a result, fluctuations in the threshold voltage are reduced. To do.

Next, an inverter (E / E) composed of a load transistor composed of a transistor having a threshold voltage fluctuation and a drive transistor connected to the load transistor.
In the shift register in which a plurality of circuits each including an inverter and a pass transistor connected to an inverter input are connected, a shift register in which a control input is connected to an input and an output of the inverter via a resistor is described above. It has the same function as the E / R inverter.

The difference is that the resistance of the load is changed to an a-Si thin film transistor and the control input is also connected to the output of the inverter through the resistance. When the circuit is at rest, like the dynamic logic circuit using the E / R inverter described above, a negative voltage is applied to the gate of the a-Si thin film transistor to change the threshold voltage negatively, and as a result, the threshold voltage changes. It will be reduced.

The gate of the pass transistor among the transistors forming the circuit is connected to the clock. When the circuit operates, the gate of the pass transistor is kept at a constant voltage V.
When it is set to H, it can be operated as it is as a static circuit.

Such a static circuit similarly constitutes a circuit by setting the power supply voltage, the ground voltage and other input voltages to appropriate values when the circuit is at rest.
Since a negative voltage can be applied to the gate of the Si thin film transistor, the threshold voltage fluctuation can be recovered.

A plurality of circuits, each of which is composed of a load resistance, an inverter composed of a drive transistor composed of a transistor having threshold voltage fluctuation connected to the load resistance, and a pass transistor connected to the input of the inverter, are continuously provided. In the shift register, different power supply lines are connected to the inverters of the odd-numbered circuit and the inverters of the even-numbered circuit in this continuous circuit, the ground line is connected to the inverter, and the clock line is connected to the gate of the pass transistor. It was done.

A power supply voltage is applied to a plurality of power supply lines when the circuit is operating, and a ground voltage is applied to a ground line. When the circuit is at rest, the plurality of power supply lines and the ground line are connected to the gates, sources and gates of the transistors constituting the circuit. The voltage is applied in such a sequence that a negative voltage is applied to the drain.

When a power supply voltage is applied to the power supply line and a ground voltage is applied to the ground line, the circuit forms a normal dynamic logic circuit in synchronization with the clock signal applied to the clock line. For example, a shift register performs an operation of shifting input data.

On the other hand, when the circuit is at rest, a sequence of applying a predetermined voltage to the ground line, the power supply line, and the clock line to apply a voltage to each of the lines, thereby applying a negative voltage to the gate of the drive transistor forming the circuit. ,
It is possible to take a sequence of applying a negative voltage to the gate of the pass transistor.

At this time, since the data shift operation which is the original operation of the circuit is not performed, the circuit operation is defined as being in a suspended state. In addition to this, there is a power-off state in which no voltage is applied to the power supply line, the ground line, and the clock line. Thus, by applying a predetermined voltage to the power supply line, the ground line, and the clock line when the circuit is at rest, the threshold voltage that fluctuates when the circuit is operating, so that the gate-source voltage and the gate-drain voltage of the transistors that configure the circuit are negative. Therefore, it is possible to recover the fluctuation of the threshold voltage.

In addition, in a circuit which is provided with a plurality of circuits, each of which is composed of a load transistor and a driving transistor, which are composed of transistors having threshold voltage fluctuations, and a pass transistor which is connected to the input of the inverter, in a continuous manner, Connect different power supply lines to the gate and drain of the load transistor, connect the ground line to the source of the drive transistor, add power supply voltage to multiple power supply lines and add ground voltage to the ground line during circuit operation, and By performing the operation method of the circuit that applies a voltage in a sequence in which a negative voltage is applied to the gate-source voltage and the gate-drain voltage of the transistor that configures the circuit on the power supply line and the ground line during rest,
It is possible to recover the fluctuation of the threshold voltage that has fluctuated during circuit operation when the circuit is at rest.

Further, in a circuit using a transistor whose threshold voltage fluctuates, the threshold voltage of the transistor which fluctuates during the operation period of the circuit is changed to the gate-source voltage and the gate whose polarity is opposite to that of the threshold voltage which fluctuates during the period when the circuit operation is stopped.・
Apply drain voltage. When the circuit is operating, the gate-source voltage is positive and the threshold voltage fluctuates positively.However, by making the gate-source voltage and the gate-drain voltage negative at rest, the threshold voltage fluctuates negatively, resulting in It recovers the fluctuation of the threshold voltage.

In addition, in a circuit using a transistor having a threshold voltage fluctuation, the threshold voltage which is changed during the period in which the circuit operation is stopped is opposite to the threshold voltage which is changed depending on the time when the positive voltage is applied to the gate-source voltage during the circuit operation period. The threshold voltage fluctuation is recovered by changing the time of applying the polar gate-source voltage and the gate-drain voltage.

Since the fluctuation of the threshold voltage depends on the time, the gate voltage depends on the time when the positive gate-source voltage is applied.
It determines the time to apply a negative voltage to the source and gate / drain.When the time dependence of positive and negative fluctuations is determined, the period for applying a negative voltage according to the fluctuation time is selected. It makes the fluctuation small enough.

When the shift register provided with the above-mentioned circuit is used for the line image sensor, the threshold voltage fluctuated during the operation of the line image sensor is restored when the operation of the sensor is stopped. Further, in order to select a large number of photoelectric conversion elements of the line image sensor and transfer the photoelectric conversion output to the outside, a circuit using a shift register, a buffer, and a transfer switch composed of transistors having threshold voltage fluctuations is used to supply a predetermined power supply voltage to a circuit. By providing a power supply drive circuit that is changed in step 1, the threshold voltage of the transistor, which fluctuates during the operation period, is restored at rest.

Further, the means for detecting and storing the operating time of the line image sensor detects and stores the operating time of the image sensor, and sends a pause signal when the image cent is inactive, so that the image sensor is in the idle state. Therefore, the fluctuation of the threshold voltage of the transistor that constitutes the circuit, which has fluctuated during the operation period, is restored at the time of suspension.

By storing the operation period of the image sensor and selecting a proper value for the rest time from the period, the fluctuation of the threshold voltage is made sufficiently small.

[0056]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an example of the circuit configuration used in the line image sensor of the present invention and an example of its operation will be described with reference to FIGS.

FIG. 1 shows a circuit composed of an inverter composed of a load resistance and an a-Si thin film transistor, and a pass transistor connected to the inverter. In the circuit, a plurality of circuits are provided in which a control input is provided to the input of the inverter through a resistance. As the shift register continuously provided, the E / R dynamic shift register used in the line image sensor is given as an example.

This shift register is constructed by connecting an E / R inverter composed of a load resistor R1 and a driving transistor D1, and four elements of a dynamic logic circuit connected to a pass transistor P1 and a control resistor RC1 at the input of this inverter. is doing. The source of the drive transistor of the inverter of each element is connected to the ground line VS, and the power source side of the load resistor R1 is alternately connected to the power source lines VD1 and VD2.

The gates of the pass transistors of the respective elements are alternately connected to the clock lines Φ1 and Φ2, and the respective control resistors are connected to the control line VC. The resistance value of the control resistor RC is 10 times or more, preferably 100 times or more larger than the load resistance R.

The circuit operation and input of the E / R dynamic shift register will be described with reference to FIG. During normal circuit operation, since the resistance value of the control resistor RC is large, the control resistor operates as if there were no control resistor. That is, as shown in a of FIG. 2, when clocks Φ1 and Φ2, which become logic 1, are alternately input to the gates of the pass transistors and data shown in FIG. 2 is input to VA1, the data is sequentially shifted to VA2. VA3, VA4, VA
5 operates as shown in the figure. At this time, the positive voltage VH is applied to the power supply lines VD1 and VD2, and the ground voltage VL is applied to the ground line VS.

The voltage of the control line VC may be either VH or VL. The ratio of the load resistance of the inverter to the on-resistance of the drive transistor is preferably 6: 1 or more.
Although not shown in the circuit diagram of FIG. 1, it goes without saying that the MIS transistor has an inherent capacity and a parasitic capacity, and is dynamically operated by charging and discharging this capacity.

During the operation of the shift register, the gate-source voltage of the pass transistor and the drive transistor is always 0 V or higher, so that the threshold voltage fluctuates positively.

Next, the input when the original circuit operation of the shift register is stopped will be described. FIG. 2b shows the conditions for negatively applying the gate / source voltage of the drive transistor and the pass transistor. In order to negatively apply the gate-source voltage of the drive transistor, the power supply lines VD1 and VD2 and the ground line VS are set to a positive voltage VH as shown by b-1 in the figure, and the clock lines Φ1 and Φ2 and the control line are controlled. Let VC be VL.

Under this condition, the pass transistors P1 and P
The gate-source voltage of 2, P3 and P4 is 0V, and the threshold voltage does not change. On the other hand, the gate of the drive transistor is VL, while the source / drain is VH, and as a result, the gate / source voltage and the source / drain voltage are negative. However, the negative voltage means VL-VH.

As a result, the threshold voltage fluctuates negatively, and there is an effect that the threshold voltage that fluctuates positively at the time of circuit operation can be restored. According to this embodiment, when the circuit operates, it operates as a normal dynamic shift register transistor,
During a pause, a simple procedure is performed by applying a predetermined voltage to the power supply line, clock line, ground line, and input data.
There is an effect that a negative voltage can be applied to the gate / source and the gate / drain of the i thin film transistor.

Here, the power supply lines VD1 and VD2 have the same operation and can be combined into one. However,
In this embodiment, since VD1 and VD2 are separated, VD
For example, the voltages of 1 and VD2 are set to VL and VH, respectively, and the clock lines Φ1 and Φ2 are set to VH, so that the inputs of the inverters of the respective stages can be simultaneously reset.

The structure of the inverter composed of a-Si thin film transistors will be described with reference to the sectional view of FIG. A gate electrode 2 made of Cr, Al, or the like is formed on an insulating substrate 1 such as glass, and a pattern is formed by using a photolithography technique. A gate insulating film 3 is formed thereon with silicon nitride, silicon oxide, or aluminum oxide, and intrinsic amorphous silicon i-a-Si4 is formed thereon.
To form.

On top of that, a large amount of phosphorus is doped to obtain a strong n
A modeled n (+)-a-Si5 is formed, and the source / drain electrodes 6 are formed of a material such as Cr or Al. The drive transistor D and the load resistor R can be formed by performing predetermined patterning on these layer configurations, and the drive transistor D has a structure called an inverted stagger type.

In addition to this, a forward stagger type transistor or a planar type transistor can be manufactured by changing the layer structure. The load resistance R shown in FIG. 3 is n (+)-a-Si.
The layer 5 is used as a resistor transistor.
The (+)-a-Si5 layer also serves as a layer forming an ohmic contact between the source / drain electrode 6 and ia-Si4 in the thin film transistor D portion. In such a structure, when a positive gate-source voltage is applied to the gate electrode 2, a channel is formed in ia-Si4 and the field effect transistor operates.

Normally, the gate electrode 2 and the source / drain electrodes 6 are formed by the sputtering method, and the gate insulating film 3, i
-A-Si4, n (+)-a-Si5 is formed by using a gas such as monosilane or ammonia as a raw material and a process such as a CVD method. A-Si formed by such a method
The thin film transistor has a carrier drift mobility of 0.
01 to 2.0 cm ² / Vsec, n having a threshold voltage of about 1 to 4 V
It becomes a channel type enhancement type MIS transistor.

The p-Si thin film transistor can be constructed by a similar process and structure. In the case of a p-Si thin film transistor, in the structure of FIG. 3, after forming ia-Si, a laser is applied to the ia-Si layer to instantaneously melt and crystallize. An argon laser, an excimer laser, or the like can be used as the laser, and since the wavelengths are different, the penetration depth is different. Crystallization is possible by setting the irradiation energy, irradiation time, irradiation sequence of these lasers and the thickness of ia-Si to appropriate values. The other structure and process may be the same as the structure described in FIG.

The p-Si thin film transistor thus formed has the advantage that it can use almost the same process as the thin film transistor using ia-Si. Like the ia-Si thin film transistor, this transistor also has the phenomenon of threshold voltage fluctuation. Further, an enhancement type MIS transistor having a carrier drift mobility of about 10 cm ² / Vsec and a threshold voltage of about 0.5 to 3 V is obtained.

When a positive voltage is applied to the gate and source of the a-Si thin film transistor formed as described above, FIG.
As described above, the threshold voltage fluctuates positively with time. The magnitude of the fluctuation depends not only on time but also on voltage and process.
In this way, the threshold voltage fluctuates over a long period of time, and the current drive capability of the transistor decreases. Eventually, the circuit operation may stop.

FIG. 5 shows an example in which the operating life of the circuit is determined from the decrease in the operating speed of the circuit, and the ratio of the positive gate voltage to the positive gate voltage and the negative voltage applied up to that time and the operating life are measured. . The life is extended significantly by applying a negative voltage as well as a positive voltage.

Further, when the negative voltage is applied with a voltage having the same absolute value, the fluctuation of the negative threshold voltage is smaller than the fluctuation of the positive threshold voltage, and therefore, with respect to the time for applying the positive voltage. As a result of the study, it is clear that it is better to apply the negative voltage for about three times.

In this way, the gate-source voltage of the a-Si thin film transistor is applied with a positive voltage when the circuit is operating and a negative voltage when the circuit is at rest, thereby a-Si
There is an effect that the reliability of a circuit using a thin film transistor can be significantly increased.

As described above, according to this embodiment, the threshold voltage of the thin film transistor used in the shift register constituting the line image sensor can be restored when the operation of the circuit is stopped, and the line image sensor with high reliability can be obtained. Also, an image reading apparatus using this line image sensor can be formed.

Another embodiment of the present invention will be described with reference to FIG. An E / E inverter is constituted by the load transistor L1 and the drive transistor D1, and the pass transistor P1 and the control resistor RC are connected to the input of this inverter.
A control resistor RC is also attached to the output of the inverter.
A shift register is configured by connecting these in multiple stages as a unit element of the circuit.

In this embodiment, this element is connected in four stages. The gate of the load transistor of each stage is the power supply line VD1
And the drain is connected to VD2. The gates of the pass transistors in each stage are alternately connected to the clocks Φ1 and Φ2. The source of the drive transistor of each stage inverter is connected to the ground line, the control resistance connected to the input of the inverter is connected to the control line VC1, and the control resistance connected to the output of the inverter is connected to the control line VC2.

In this embodiment, the power supply lines VD1 and VD2 are set to the positive voltage VH, and the ground line VS is set to the ground voltage VL.
When a voltage corresponding to the input data is applied to VA1 and a clock signal is applied to the clock lines Φ1 and Φ2 as shown in the figure, the data is shifted as in the operation of the embodiment of the E / R inverter shown in FIG. 1 described above. To operate. Since the operation is the same, it is omitted.

Also in this embodiment, the load transistor L
The ratio of the ON resistance of 1 to the drive transistor D1 is 6: 1 or more, and the control resistance RC is 10 times or more, preferably 100 times or more larger than the ON resistance of the load transistor. Since the value of the control resistance is large, the shift register performs the data shift operation during the normal dynamic operation regardless of the voltages of the control lines VC1 and VC2. On the contrary,
The value of the control resistor will be determined within a range that has almost no effect on the dynamic operation.

Therefore, it is necessary to increase the resistance value of the control resistor in a circuit having a low operation speed, and in the circuit having a high operation speed, the control resistor may have a smaller resistance value. In either case, it is a necessary condition that the data charged in the capacitor at the gate of the inverter is not discharged within the retention time of the dynamic operation. This point is the same as in the previous E / R inverter embodiment.

Next, the operation when the negative gate voltage is applied to the a-Si thin film transistor when the E / E inverter of this embodiment suspends the data transfer operation will be described. Since all the a-Si thin film transistors forming the E / E inverter of this embodiment are applied with a positive gate-source voltage during operation, the threshold voltage thereof fluctuates with the operation time.

If the negative application operation is not performed as it is, the circuit does not operate for a long time. Therefore, in this embodiment, a negative voltage is applied to the gate of the transistor by applying an appropriate voltage to the power supply lines VD1, VD2, clock lines Φ1, Φ2, ground line VS, control lines VC1, VC2, and input VA1, By this, the fluctuation of the threshold voltage is canceled positively and negatively, and long-term operation reliability is secured.

As a condition for negatively applying the gate-source voltage of the drive transistor and the load transistor, VD
1, φ1, φ2, VC1 is VL, VD2, VC2
Let VS be VH. Also, the gate of the pass transistor
Conditions for applying a negative source voltage are VC1, VC
2, VS is VH, and φ1 and φ2 are VL. Thus, the reason why the two negative application conditions are used is that a negative voltage cannot be applied to the gates and sources of all transistors at the same time. If the conditions shown in the figure are used, the gate-source voltage becomes negative, and there is an effect that the fluctuation of the threshold voltage that has changed to positive during circuit operation can be canceled.

The resistance value of the control resistor RC is preferably large in order to reduce the influence on the dynamic operation. However, since the transistor has a leak resistance, the resistance value is smaller than the resistance value by one digit or more. You need to use a value. According to the present embodiment, there is an effect that the threshold voltage that has changed positively during the operation of the E / E dynamic shift register is negatively changed during cancellation and is cancelled, so that the operation can be performed for a long time.

The shift register using the E / R inverter can charge at a high speed because the load is a resistance, and therefore can perform a high-speed circuit operation. On the other hand, there is a variation in the resistance value due to a variation in the process. Tend to be susceptible to On the other hand, in the E / E inverter, the inverter ratio can be determined only by the pattern shape of the channel width and the channel length, so that there is an effect that process variations can be absorbed.

Since the application time of the positive gate-source voltage applied to each a-Si thin film transistor differs depending on the data, it is necessary to control the negative application time accordingly.

In this embodiment, the power supply line of the inverter is only VD2 except VD1. By providing two power supply lines as in the example of the E / R inverter (FIG. 1), the shift register is also provided at once. Can be reset.

As described above, according to the present embodiment, the threshold voltage of the thin film transistor used in the shift register which constitutes the line image sensor can be restored when the operation of the circuit is stopped, and the line image sensor with high reliability can be obtained. Also, an image reading apparatus using this line image sensor can be formed.

Another embodiment will be described with reference to FIG. This is an E / R shift register. The load resistor R1 and the drive transistor D1 constitute an E / R inverter, and the input of this inverter is connected to the pass transistor P1 for controlling the input of data. In this shift register, the elements are connected in four stages, and the gates of the pass transistors in each stage are alternately connected to the clocks Φ1 and Φ2.

The power source of the inverter of each element is the power source line VD1.
, And VD2 alternately, and the source of the drive transistor is connected to the ground line. This constitutes a dynamic E / R shift register.

FIG. 8 shows the circuit operation of the E / R shift register and the sequence of gate / source negative application when the circuit is at rest. During operation of the shift register, power supply lines VD1 and VD2
Is applied to the ground line VS, and the ground line VS applies the ground voltage VL. Then, clocks Φ1, Φ
2. Shift data as shown for 2 and data input.

When the shift register is at rest, the power supply lines VD1,
When a voltage is applied to VD2, clock lines Φ1 and Φ2, and the ground line at appropriate timing, a negative voltage can be applied to the gate and source of the drive transistor and the pass transistor that form the shift register.

FIG. 8B-1 shows a sequence for applying a negative voltage to the gate and source of the thin film transistor.
First, an element constituted by the pass transistor P1, the load resistor R1 and the drive transistor D1 will be described. Clock Φ1
Is set to VH for a short time, and at the same time VA1 is set to VL, the gate voltage VB1 of the drive transistor D1 is set to VL.
Voltage. Next, the clock Φ1 is set to VH to cut off the pass transistor, and the voltage of VL is held in the capacitance of the circuit node of VB1.

At this time, the power supply line VD2 and the ground line VS
Are both VH voltage, drive transistor D
A voltage of VL-VH, that is, a negative voltage can be applied to the gate-source voltage of 1. Since the drive transistor D3 forming the third element has the same connection configuration, the gate-source voltage is similarly applied to the negative.

Similarly, the second and fourth elements are the clock Φ.
2 and the power supply VD2 are synchronized to set the gate voltage of the drive transistor to VL, and then the source / drain voltage to VH.
In this state, a negative gate-source voltage can be applied.

At time t1 for setting the gate of the drive transistor to the voltage VL, when the capacitance at the gate of the drive transistor is C and the combined resistance of the load resistance R and the pass transistor P is RT, the product of them is taken as the time constant. It becomes the value to do.

The time t2 when the gate-source voltage becomes negative is the time when the product of the capacitance C and the value RL of the leak resistance is a time constant. The actual value is 10 μs for the former
The latter is 100 μs, whereas the latter is 10 ms to 100 m
s, and a sufficiently negative voltage can be applied.

The timing of setting the gates of the drive transistors of the odd-numbered elements and the even-numbered elements of the shift register to VL is different because the gate voltage of the drive transistor changes due to the voltage change through the parasitic capacitance. This is because consideration is given to making it as small as possible. That is, using the first element, the drain of the drive transistor D1 is connected to the power supply line V2, and VB1
This is to prevent a phenomenon in which when the voltage of VD2 changes from VL to VH after the voltage of VL is set to VL, the voltage division of the voltage occurs due to the capacitance of the gate and the drain and the voltage of VB1 rises.

On the other hand, in order to negatively apply the gate-source voltage of the pass transistors P1 to P4, the line b- of FIG.
As shown in FIG. 2, the short-time clocks Φ1 and Φ2 are set to VH, the pass transistors are made conductive, and the voltages from VB1 to VB4 are set to VH (strictly, a voltage lower by the threshold voltage), and then the clocks Φ1 and Φ2 are set to the voltage VL. To do.

At this time, the voltage of the power supply lines VD1 and VD2 and the ground line VS is VH, so that the source / drain and the drain of the pass transistor are at the voltage of VH. In this way, the gate-source voltage of the pass transistor can be made negative, which has the effect of ensuring long-term circuit reliability.

Since the positive gate voltage is applied to the gate of each transistor for different periods during the operation of the circuit, it is necessary to change the negative application time correspondingly. In the present embodiment, the sequence is more complicated than that of the embodiments of FIGS. 1 and 6, but there is an effect that a negative gate voltage can be applied when the circuit is inactive without increasing the number of circuit elements.

By using the circuit configuration of the shift register and the method of operating the circuit as described above, the drift of the threshold voltage of the thin film transistor can be recovered and the line image sensor having high reliability and this line can be recovered as in the above-described embodiments. An image reading device using an image sensor can be formed.

FIG. 9 shows an embodiment of a shift register circuit using an E / E inverter. This circuit is different from the embodiment shown in FIG. 6 in the control resistor RC and the control lines VC1 and VC.
It is a standard E / E shift register with 2 removed.

During the dynamic operation, the circuit operation as shown in FIG. 10A is performed, but since it is the same operation as the circuit of the embodiment shown in FIG. 6, its explanation is omitted. When the circuit is operating, a positive voltage is applied to the gate of the transistor that constitutes the circuit, so that the threshold voltage of the transistor fluctuates positively. In order to recover the fluctuation of the threshold voltage, it is necessary to apply a negative voltage to the gate / source and the gate / drain of the transistor.

To make the gate-source voltages of the drive transistors D1 to D4 and the load transistors L1 to L4 negative, the sequence of b in FIG. 10 is used. The clocks Φ1 and Φ2 are used as the voltage of VH for a short time to make the pass transistor conductive, and at the same time, the voltage of the power supply line VD1 is set to VH to make the load transistor conductive, and the power supply line VD2 is set to V
By setting the voltage to L, the voltage at the nodes of the gates VB1 to VB4 of the drive transistor is set to VL.

Next, the clock lines Φ1 and Φ2 are set to VL to make the pass transistors non-conductive to hold the potentials of VB1 to VB4, and the next power supply line VD2 is set to VH to VA.
The voltage at the node between 2 and VA5 is VH. Next, by setting VD1 to VL, the gate-source voltage of the drive transistor and the load transistor can be made negative.

The sequence for making the gate and source voltages of the pass transistor and the load transistor negative is shown in FIG.
It is shown in c of 0. The clock lines Φ1 and Φ2 are set to VH for a short time to make the pass transistor conductive, and at the same time, the power supply line VD1 is set to VH for a short time to make the drive transistor conductive. At this time, power supply line VD2, input VA
1. Since the ground line VS has a constant voltage VH, the gates VB1 to VB4 of the drive transistor are charged to VH.

Next, the clock lines Φ1 and Φ2 are set to VL to make the pass transistor non-conductive, and then VD1 is set to VL to make the load transistor non-conductive. As a result, the source and drain of the pass transistor are approximately VH.
The gate-source voltage becomes negative because the gate becomes VL. At this time, the driving transistor and the load transistor have VH in the gate, the source, and the drain, and the threshold voltage does not change.

As described above, the sequence of negative gate voltage application in the embodiments described with reference to FIGS. 7 and 9 utilizes the point that the voltage is held in the capacitor by being disconnected from the power supply line when the transistor becomes non-conductive. In order to make the gate-source voltage of the transistor negative, the capacitance of the circuit node constituted by a predetermined wiring capacitance and the capacitance of the transistor is charged in advance.

According to the present embodiment, the circuit operates as a dynamic shift register during the operation of the circuit, and the gate-source voltage can be made negative when the circuit is inactive. This has the effect of enabling the operation of the time circuit.

Another embodiment of the present invention will be described with reference to FIGS. 1, 6, 7 and 9. When creating a drive circuit for a line image sensor, not only a dynamic circuit but also a static circuit is necessary. The dynamic circuit can easily achieve the data transfer by switching the pass transistor, but has a drawback that the capacitance is charged and discharged as the pass transistor is turned on and off, resulting in noise.

On the other hand, the static circuit is indispensable for the buffer circuit that shapes the waveform and expands the current driving capability. However, since the static circuit is a circuit in which the inverter and the next-stage inverter are directly connected and the output is determined when the input is determined, a
It was difficult to apply a negative voltage to the gate of the -Si thin film transistor.

In this embodiment, the circuits shown in FIGS. 1, 6, 7 and 9 are used as they are as static circuits. When the circuit is operating, V is applied to the clock lines Φ1 and Φ2 in the figure.
A voltage of H is applied so that the output of the inverter is always in a conductive state so that the output of the inverter is directly connected to the next-stage inverter in a circuit manner.

Also, when the circuit is at rest, it is already shown in FIGS.
A negative voltage can be applied to the gate of the transistor by using the sequence described in FIGS. According to this embodiment, the gate voltage is made negative at the time of rest and the driving of the threshold voltage is canceled, so that there is an effect that it is possible to provide a static circuit that enables long-term circuit operation.

Further, since the dynamic circuit and the static circuit have the same structure, there is an effect that the negative gate voltage application sequence at the time of rest does not become complicated even in a circuit in which these circuits coexist.

Another embodiment of the present invention will be described with reference to FIG. FIG. 11 is a block diagram of a line image sensor incorporating the circuits of the above-described embodiments. A shift register 11, a buffer 12, and a transfer switch 1 formed of an amorphous silicon thin film transistor on the image sensor substrate 10.
4, a photoelectric conversion element 13 made of amorphous silicon and a signal matrix 15 are formed.

The image sensor board 10 has a power supply driving circuit 20, a timing control circuit 21, and a signal detection circuit 22 outside the image sensor substrate 10. The external terminal 30 supplies a start signal SP serving as a power supply and an operation reference, a clock CLK, an operation and Input the MODE signal to specify the pause and read the signal VID
It is configured to output EO.

In the reading mode, the shift register 11
After resetting, the S /
The block selection signal is sequentially shifted from R1 to S / Rn. This signal shapes the waveform through the buffer 12 and increases the current driving capability to sequentially select the transfer switches 14 block by block.

When the block B1 is selected, the transfer switch of the connected block becomes conductive, and the charges photoelectrically converted by the photoelectric conversion element 14 are transferred to the signal matrix 15. The photoelectric conversion signal transferred to the signal matrix 15 is amplified and parallel-serial converted by the detection circuit 22, and is output to the outside as a read signal VIDEO.

In such an operation, the timing control 21 generates a control signal based on the start signal SP inputted from the external terminal 30, the clock signal CLK which is the reference timing, and the MODE signal for designating the operation or non-operation,
This is performed by operating the detection circuit and the power supply drive circuit at a predetermined timing.

On the other hand, when the pause is designated from the outside by the MODE, the image sensor enters the pause mode, and a sequence in which a negative voltage is applied to the gate of the a-Si thin film transistor which constitutes the shift register 11, the buffer 12 and the transfer switch is set. take. The shift register 11 and the buffer 12 use any one of the circuits of FIGS. 1, 6, 7, and 9 described above. Although the dynamic shift register or the buffer can be configured as it is in FIGS. 1, 6, 7, and 9, there is a degree of freedom in the circuit because a NOR logic circuit can be easily manufactured.

The circuit of this embodiment shown in FIG. 11 is usually formed by laminating thin films such as a-Si and p-Si on a glass substrate, assembled with a light source on a base, and used for reading an original. An example of a cross-sectional view of this embodiment is shown in FIG.

A gate electrode 2 is formed on a transparent glass substrate 1 to form a gate insulating film 3, i-a-Si 4, n (+)-a-.
The Si 5, the electrode 6, the passivation film 7, and the electrode 8 also serving as the light shielding film are sequentially formed by stacking and patterning.
As a result, functional elements such as the reference element 102a, the reading element 102b, the signal capacitor 105, and the thin film transistor 103 are formed.

The glass substrate is mounted on the base 106 together with the LED light source 101, and the satin conductive film 104 is further mounted for reading the original. The original 500 is pressed against the sensor by the platen roller 401 and is read. Here, the satin conductive film is a transparent film that is elastically deformable, has a conductive area resistance of 100 KΩ / □ or less, and has a concavo-convex surface on the side that contacts the sensor surface, which scatters light. A film that has become a surface.

Further, the film is mounted so that the satin finish of the satin conductive film is on the side of the reading sensor substrate. This is because the light from the light source illuminating the original from the back of the substrate is scattered on the satin finish on the film surface. Therefore, it is possible to prevent the reading output from being abnormal due to the condensing due to reflection when the document is deformed into a concave mirror shape due to the deformation of the film in a state of being pressed and brought into close contact.

That is, by mounting the conductive transparent film on the substrate, it is possible to obtain an image sensor with stable reading performance and easy to manufacture. The conductive transparent film is easily elastically deformed when a load is applied, so that it is not easily damaged. Further, since the conductive transparent film serves as a shield against electric waves and induction of static electricity, it has an effect of preventing noise in the output signal of the image sensor.

Since it serves as a spacer between the document surface and photoelectric conversion, it also serves as a spacer for securing the illumination light and as a wear-resistant protective film. Because of these effects,
An image sensor to which this film is applied has a good assembling property and has an effect of enabling stable reading.

For reading an original, two reading elements 102b and a reference element 102a are used as one set. Although these photoelectric conversion elements are expressed in a circuit as a resistance circuit as shown in FIG. 11, the photoelectric conversion element is actually a photoconductor made of a-Si, and the resistance changes according to the amount of incident light.
The operation of these two elements is as follows.

The reading element 102b is formed by the light-shielding film 2a so as not to directly receive the light of the light source 101, and the light source 101 receives the reflected light illuminating the original 500 and photoelectrically converts it. At this time, the light-shielding film 8 is formed on the reference element 102a, and the reflected light from the document 500 does not enter. The photoelectric conversion output of the reading element 102b is proportional to the illuminance and reflectance of the document 500.

Since the photoelectric conversion output of the reference element 102a is proportional to the radiation intensity of the light source 101, the reading element 1
If correction is performed using the photoelectric conversion output of 02b, it is possible to obtain an output that does not depend on the unevenness of the illuminance of the original, that is, the unevenness of the radiation intensity of the light source, but only on the reflectance of the original. In this embodiment, the reading element 102b is connected to the reference element 102a in series, and the read output signal is output as a voltage at the connection point A between the reading element 102b and the reference element 102a.

Further, the signal capacitor 105 is formed in parallel with the reading element 102b, and has a voltage Vsig at the connection point A.
And the signal charge Qsi determined by the electrostatic capacitance Csig of the reading capacitance
Store g = Csig × Vsig. For each reading cycle, the transfer switch 14 is turned on to transfer charges to the signal line and read.

According to the present embodiment, the threshold voltage of the a-Si thin film transistor that has changed positively during the operation period of the circuit is changed to the negative threshold voltage by performing the sequence in which the gate / source voltage is negative during the rest period of the circuit. Can be canceled, so that there is an effect that reliability of circuit operation for a long period can be secured.

Further, since the driving circuits such as the shift register and the buffer can be formed on the image sensor substrate, there is an effect that the number of wirings can be reduced and a small sensor can be constructed.

Further, since the line image sensor of this embodiment performs reading in close contact with the original, a very small reading system can be constructed.

Further, according to this embodiment, since an output voltage determined by the ratio of the reading element and the reference element is obtained, there is an effect that a stable reading can be performed regardless of the variation of the light source.

In addition, according to this embodiment, the satin conductive film can prevent static electricity noise and abnormal optical reflection, so that stable reading can be achieved.

Another embodiment of the present invention will be described with reference to FIG. FIG. 13 is a block diagram of a facsimile apparatus which is one of the image reading apparatuses incorporating the line image sensor of the present invention. The line image sensor 100, the recording head 300, and the mechanical system 400 are controlled by the control / power supply circuit 200 and the power supply is controlled. The structure which supplies is shown. The control / power supply circuit 200 includes a CPU 202, a ROM 208, and an RA.
M209, MODEM210, NCU211, sensor control / detection circuit 203, recording control circuit 204, mechanism control circuit 205, input / output interface 206, power supply 20
7 and a clock 201.

The clock 201 determines the operation timing of the control / power supply circuit 200 including the CPU 202. CPU
Reference numeral 202 indicates RO in synchronization with the clock signal of the clock 201.
The operation of the facsimile apparatus is controlled according to the software prepared in M208.

The RAM 209 is a memory for temporarily storing image data and control data, and is a work area when viewed from software.

The MODEM 210 converts a voice band signal from an external circuit into a digital signal and converts the digital signal into a voice band signal and sends the digital signal to the line. Also, NC
U211 controls connection with an external line.

The sensor control / detection circuit 203 includes a clock for driving the line image sensor 100, a start signal,
A mode signal for designating an operation or a pause is output, an analog signal read from the sensor is detected, and multivalued digital data is obtained according to the purpose.

The recording control circuit 204 transfers recording data to the recording head 300 such as a thermal recording head and controls recording. The mechanism control circuit 205 controls the mechanism system 400 by conveying recording paper or a read document by a motor, detecting abnormal feeding of the paper, detecting the document, and the like.

The input / output interface 206 is an interface with an operator who displays the state of the input and facsimile such as the input of the telephone number and the designation of the document density.

The power supply circuit 207 includes the circuit blocks of the control / power supply circuit 200 and the line image sensor 10.
0, the recording head 300, and the mechanical system 400 are supplied with power source power. Further, the control power supply circuit 200 includes an image sensor 100, a recording head 300,
When the mechanical system 400 is not used, it has a function of cutting off the power supply of that portion by a relay or the like.

At the time of copying an original or sending a fax, the line image sensor is supplied with a power source and a control signal to perform an original reading operation. As described above, when the line image sensor uses a transistor having a threshold voltage fluctuation, the threshold voltage of the transistor changes positively during this operation period. At the time of operation, for example, the MODE signal shown in FIG. 11 specifies the operation mode, and the line image sensor enters the operation mode.

This operating time is detected by the CPU 202 on the basis of the clock signal, and is a RAM as a storage means.
209 is stored. When the reading is completed and the operation of the line image sensor becomes unnecessary, the CPU 202 specifies the sleep mode, and the line image sensor enters the sleep mode.

In the sleep mode, the gate-source voltage and the gate-drain voltage of the transistors forming the drive circuit of the line image sensor are set to be negative, and the changed threshold voltage is restored. It is necessary to change the rest time according to the operating time to suppress the threshold voltage fluctuation.

In this embodiment, an appropriate pause time is determined based on the operation time stored in the RAM, a pause signal for operation is sent to the sensor, and when the pause time ends, the power supply circuit 2
The power of the line image sensor is turned off by designating power off in 07. In this way, in the facsimile machine, by setting the idle time with respect to the sensor operating time to an appropriate value, the threshold voltage fluctuation of the transistor is recovered,
There is an effect that it can be operated for a long time.

FIG. 14 is a schematic sectional view of the line image sensor when it is mounted on a facsimile machine. Case 40
4, the line image sensor 100 is pressed against the platen roller 401 with spring support to form a reading system, and the thermal recording head 400 is supported with spring to support the platen roller 4.
Press on 02. In addition, a recording paper 403 and a control / power supply circuit 200 are incorporated.

The original 500 is read by the line image sensor at the time of reading the original, and is recorded on the recording paper 403 by the recording head 400 at the time of recording. The paper is conveyed by rotating the platen rollers 401 and 402 using, for example, a pulse motor. As described above, by mounting the small sensor, the facsimile apparatus can be downsized, and the degree of freedom in design can be further increased.

In this embodiment, the facsimile apparatus is taken up as an image reading apparatus using the line image sensor, but the line image sensor is a copying machine,
The same can be applied to image scanners and the like.

[0154]

According to the present invention, the dynamic circuit or the static circuit which constitutes the shift register by operating the power supply line, the ground line, the clock line and the control line at a predetermined voltage performs a predetermined function during operation. When the circuit is at rest, the a-Si thin film transistor or p- that forms the circuit
It is possible to negatively apply the gate-source voltage and the gate-drain voltage of a transistor having a threshold voltage fluctuation such as a Si thin film transistor.

Therefore, the shift register which restores the threshold voltage of the transistor which has been positively changed during the circuit operation to the original value and enables the circuit operation for a long time, the line image sensor using this shift register, and this line An image reading device using an image sensor can be formed.

According to the present invention, in a line image sensor using a thin film transistor having a threshold voltage fluctuation in a drive circuit, fluctuations in the threshold voltage of the transistor that occur during the circuit operation period can be recovered during the idle period of the circuit. This has the effect of enabling the circuit operation during the period. further,
Since the driving circuit for the a-Si thin film transistor can be formed on the image sensor substrate, the number of wirings can be reduced, and a small line image sensor can be provided.

According to the present invention, in the image reading device such as a facsimile machine, a copying machine, an image scanner, etc., the threshold voltage of the transistor constituting the drive circuit of the image sensor, which detects and stores the operation period of the image sensor and fluctuates at the time of reading the original. By sending a pause signal corresponding to the operating time to the image sensor, there is an effect that the threshold voltage can be restored by performing a recovery operation during the sensor pause.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an E / R dynamic shift register according to an embodiment of the present invention.

FIG. 2 is a sequence diagram illustrating the operation of the circuit of FIG.

FIG. 3 is a cross-sectional view of an inverter including an amorphous thin film transistor.

FIG. 4 is a diagram showing how the threshold voltage of an amorphous silicon thin film transistor varies.

FIG. 5 is a diagram showing the life of a circuit.

FIG. 6 is a circuit diagram of an E / E dynamic shift register according to another embodiment.

FIG. 7 is a circuit diagram of an E / R dynamic shift register according to another embodiment.

FIG. 8 is a diagram showing the circuit operation of the embodiment of FIG.

FIG. 9 is a circuit diagram of an E / E dynamic shift register according to another embodiment.

FIG. 10 is a diagram showing the circuit operation of the embodiment of FIG.

FIG. 11 is a circuit block diagram of a line image sensor of another embodiment.

FIG. 12 is a schematic cross-sectional view of an image sensor and document reading.

FIG. 13 is a block diagram of a facsimile device.

FIG. 14 is a schematic sectional view of a facsimile device.

[Explanation of symbols]

VD1, VD2 ... Power line, Φ1, Φ2 ... Clock line, V
S ... Ground wire, R1-R4 ... Load resistance, D1-D4 ...
Drive transistors, R1 to P4 ... Pass transistors, V
C ... Control lines, RC1 to RC4 ... Control resistors, 10 ... Line image sensor substrate, 11 ... Shift register, 12 ... Buffer, 20 ... Power supply drive circuit, 100 ... Line image sensor, 103 ... Thin film transistor, 201 ... Clock, 202 ... CPU, 203 ... Sensor control / detection circuit,
209 ... RAM, 400 ... Recording head, 401 ... Platen roller, 500 ... Original.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04N 1/04 103 E 7251-5C

Claims (30)

[Claims] 1. A line image sensor for transferring a photoelectric conversion output of a photoelectric conversion element to an external circuit by a shift register, a buffer and a transfer switch is housed in a casing together with a control system, wherein the shift register has a threshold voltage fluctuation. And a means for detecting and storing the operating time of the line image sensor, and a threshold voltage of the transistor which varies in accordance with the operating time of the line image sensor detected by the means in an image reading apparatus including the transistor. And a means for generating a signal for recovering the power of the original when the reading of the original is stopped, and a power supply is input to change the power supply voltage in accordance with a control signal from the control system. An image reading apparatus including a power supply drive circuit. 2. A line image sensor, which is formed by continuously forming a plurality of circuits each including an inverter and a pass transistor connected to an input of the inverter, is housed in a casing together with a control system. In an image reading apparatus including a load resistance and a drive transistor connected to the load resistance and having a threshold voltage fluctuation, a control line is connected to the input of the inverter via a control resistance having a resistance value larger than the load resistance. Controlling, connecting different power lines to the inverters of the odd-numbered circuits and the inverters of the even-numbered circuits in the plurality of continuous circuits, connecting the ground line to each of the inverters, and the pass transistors of the odd-numbered circuits. And an image reading apparatus in which different clock lines are connected to the gates of pass transistors of circuits at even positions 3. A line image sensor, which is formed by continuously forming a plurality of circuits each including an inverter and a pass transistor connected to the input of the inverter, is housed in a casing together with a control system. In an image reading apparatus including a load transistor and a drive transistor each including a transistor having a threshold voltage fluctuation, a control line is provided to an input and an output of the inverter via a control resistor having a resistance value larger than an ON resistance of the load transistor. Connecting different power supply lines to the gate and drain of the load transistor of the inverter, connecting the ground line to the source of the driving transistor, and connecting the pass transistor and the even position of the odd-numbered circuit of the plurality of continuous circuits. Do not connect different clock lines to the gates of the circuit pass transistors. Image reading apparatus characterized by. 4. A transistor having a variation in threshold voltage is an amorphous silicon thin film transistor or a polycrystalline silicon thin film transistor.
The image reading device according to any one of 1. 5. A gate-source of a transistor having a threshold voltage fluctuation which constitutes a circuit when a circuit constituting a line image sensor is in operation, a power source voltage is applied to a power source line and a ground voltage is applied to a ground line when the circuit is inactive. A method of operating an image reading apparatus, characterized in that a voltage is applied to a power supply line, a ground line, and a control line so as to apply a negative voltage. 6. An inverter comprising a load resistor, a drive transistor connected to the load resistor and having a threshold voltage fluctuation, and a source connected to a ground line, and a pass transistor connected to the input of the inverter. In an operating method of an image reading apparatus including a line image sensor in which a plurality of circuits each including a plurality of circuits are continuously formed, different power supply lines are provided to load resistances of circuits at odd positions and circuits at even positions of the plurality of circuits. When connecting the plurality of continuous circuits, a power supply voltage is applied to the plurality of power supply lines and a ground voltage is applied to the ground line,
An image reading apparatus characterized in that a voltage is applied to a plurality of power supply lines and a ground line in a sequence in which a negative voltage is applied to a gate / source and a gate / drain of a transistor constituting the circuit in which the plurality of circuits are continuous when the circuit is stopped. How it works. 7. A line image sensor, in which a plurality of circuits each including an inverter and a pass transistor connected to an input of the inverter are continuously formed, is housed in a casing together with a control system. In an operating method of an image reading apparatus including a load transistor and a drive transistor, each of which has a threshold voltage fluctuation, a different power supply line is connected to a gate and a drain of the load transistor, and a ground line is connected to a source of the drive transistor. However, a power supply voltage is applied to the different power supply lines during the operation of the plurality of continuous circuits, and a negative voltage is applied to the gate / source and the gate / drain of the transistors forming the circuit on the power supply line and the ground line when the circuit is idle. Image reading characterized by applying voltage in the sequence of applying Method of operation of the apparatus. 8. The method of operating an image reading apparatus according to claim 5, wherein the transistor having a threshold voltage fluctuation is an amorphous silicon thin film transistor or a polycrystalline silicon thin film transistor. 9. A plurality of circuits, each comprising an inverter and a pass transistor connected to the input of the inverter, are continuously formed, wherein the inverter comprises a load resistor and a threshold voltage connected to the load resistor. In a line image sensor including a shift register including a driving transistor composed of a variable transistor, a control line is connected to the input of the inverter via a control resistor having a resistance value larger than that of a load resistor. In the plurality of continuous circuits, different power supply lines are connected to the inverters of odd-numbered circuits and the inverters of even-numbered circuits, and ground lines are connected to each of the inverters, and pass transistors and even-numbered circuits of the odd-numbered circuits are connected. A line image characterized in that different clock lines are connected to the gates of the pass transistors of the position circuit. Jisensa. 10. A drive circuit comprising a plurality of circuits each comprising an inverter and a pass transistor connected to the input of the inverter, the inverter comprising a load transistor and a drive transistor each of which has a threshold voltage fluctuation. In a line image sensor including a shift register including a transistor, a control line is connected to an input and an output of the inverter through a control resistor having a resistance value larger than an on resistance of a load transistor, and the inverter Different power lines are connected to the gates and drains of the load transistors, the ground lines are connected to the sources of the drive transistors, and the gates of the pass transistors of the odd-numbered circuits and the pass transistors of the even-numbered circuits of the plurality of continuous circuits are connected. It is characterized by connecting different clock lines to Line image sensor that. 11. A shift register, a buffer, a transfer switch, a substrate having a photoelectric conversion element and a signal matrix formed of transistors having threshold voltage fluctuations, a power supply and a control system, and a photoelectric conversion output of the photoelectric conversion element being an external circuit. In the line image sensor for transferring to the power supply, the power supply voltage is changed according to a control signal from the control system, and a power supply drive circuit for generating different voltages when the sensor is operating and when it is inactive is provided. A line image sensor characterized in that 12. A transistor having a variation in threshold voltage is an amorphous silicon thin film transistor or a polycrystalline silicon thin film transistor.
11. The line image sensor according to any one of 11. 13. A method of operating a line image sensor, comprising: a shift register formed by continuously forming a plurality of circuits each having an inverter, wherein the inverter comprises a transistor having a threshold voltage fluctuation. When recovering the threshold voltage of the transistor that fluctuates during the period, during the operation suspension period of the circuit, a voltage having a polarity opposite to the polarity in which the threshold voltage fluctuates is applied to the gate of the transistor.
A method for operating a line image sensor, characterized by adding to a source and a gate / drain. 14. A method of operating a line image sensor, comprising: a shift register in which a plurality of circuits each including an inverter are continuously formed, wherein the inverter comprises a transistor having a threshold voltage fluctuation. When recovering the threshold voltage of the transistor that fluctuated during the period, the polarity of the threshold voltage fluctuated according to the time when a positive voltage was applied to the gate-source voltage of the transistor, and the opposite polarity voltage was applied to the gate-source and gate-drain. A method of operating a line image sensor, wherein recovery is performed in addition to an operation idle period of the circuit. 15. A transistor having a threshold voltage fluctuation is an amorphous silicon thin film transistor or a polycrystalline silicon thin film transistor.
4. The method for operating the line image sensor according to any one of 4 above. 16. A circuit comprising a plurality of inverters each comprising a load resistor and a drive transistor connected to the load resistor and having a threshold voltage variation and a pass transistor connected to an input of the inverter, being connected in series. In the shift register provided, the control line is connected to the input of the inverter via a control resistor having a resistance value larger than the load resistance,
Different power lines are connected to the inverters of the odd-numbered circuits and the inverters of the even-numbered circuits in the plurality of continuous circuits, the ground lines are connected to the inverters, and the pass transistors and the even-numbered circuits of the odd-numbered circuits are connected. A shift register in which different clock lines are connected to the gates of the pass transistors of the circuit. 17. A shift register formed by continuously forming a plurality of circuits each including an inverter composed of a load transistor and a driving transistor, which are composed of transistors having threshold voltage fluctuations, and a pass transistor connected to the input of the inverter. In, the control line is connected to the input and output of the inverter through a control resistor having a resistance value larger than the on-resistance of the load transistor, and different power supply lines are connected to the gate and drain of the load transistor of the inverter to drive. A shift register characterized in that a ground line is connected to the source of the transistor, and different clock lines are connected to the gates of the pass transistors of the odd-numbered circuits and the pass transistors of the even-numbered circuits of the plurality of continuous circuits. . 18. A transistor having a variation in threshold voltage is an amorphous silicon thin film transistor or a polycrystalline silicon thin film transistor.
The shift register according to any one of 1. 19. A power supply voltage is applied to a power supply line and a ground voltage is applied to a ground line when the shift register operates, and a negative voltage is applied to a gate and a source of a transistor having threshold voltage fluctuation which constitutes the shift register when the shift register is in a rest state. A method of operating a shift register, characterized in that a voltage is applied to the power supply line, the ground line, and the control line as well. 20. A plurality of circuits, each of which comprises an inverter composed of a load resistance and a drive transistor connected to the load resistance and having a threshold voltage fluctuation, and a pass transistor connected to an input of the inverter, are connected in series. In the operating method of the formed shift register, a control line is connected to an input of the inverter through a control resistor having a resistance value larger than a load resistance, and an inverter and an even position of the odd-numbered circuit of the plurality of continuous circuits are connected. Connect different power lines to the inverter of the circuit, connect the ground line to the inverter,
Different clock lines are connected to the gates of the pass transistors of the odd-numbered circuit and the pass transistors of the even-numbered circuit, and when the shift register operates, a power supply voltage is applied to a plurality of power supply lines and a ground voltage is applied to the ground line. The operation of the shift register characterized in that when the shift register is at rest, a voltage is applied to a plurality of power supply lines and ground lines in a sequence in which a negative voltage is applied to the gate / source and gate / drain of the transistors constituting the circuit. Method. 21. A shift register formed by continuously forming a plurality of circuits each including an inverter composed of a load transistor and a drive transistor, which are composed of transistors having threshold voltage fluctuations, and a pass transistor connected to the input of the inverter. In the operating method described above, different power supply lines are connected to the gate and drain of the load transistor of the inverter, a ground line is connected to the source of the drive transistor, and a power supply voltage is applied to the plurality of power supply lines during operation of the shift register to obtain a ground line. Is applied with a ground voltage, and when the shift register is at rest, a voltage is applied in a sequence such that a negative voltage is applied to the gate / source and gate / drain of the transistors constituting the circuit to the plurality of power supply lines and ground lines. And how to operate the shift register. 22. A gate-source and a gate-drain of a transistor, wherein a threshold voltage of a transistor that fluctuates during an operation period of a shift register including a transistor having a threshold voltage fluctuation is set to a voltage having a polarity opposite to a polarity of the fluctuation of the threshold voltage. A method of operating a shift register, further comprising: recovering the shift register in addition to a rest period. 23. A threshold voltage of a transistor which varies during an operation period of a shift register including a transistor having a threshold voltage variation, the threshold voltage depending on a time when a positive voltage is applied to a gate-source voltage of the transistor. A method of operating a shift register, characterized in that a voltage having a polarity opposite to that of the changed voltage is restored to the gate / source and gate / drain of the transistor in addition to the idle period of the shift register. 24. A transistor having a threshold voltage fluctuation is an amorphous silicon thin film transistor or a polycrystalline silicon thin film transistor.
0. A method of operating the shift register according to any one of 0, 21, 22, and 23. 25. The image reading apparatus according to claim 2, wherein the control resistance has a resistance value which is 10 times or more larger than the load resistance. 26. The image reading apparatus according to claim 3, wherein the control resistance has a resistance value which is 10 times or more as large as the on resistance of the load transistor. 27. The line image sensor according to claim 9, wherein the control resistance has a resistance value which is 10 times or more as large as the load resistance. 28. The line image sensor according to claim 10, wherein the control resistance has a resistance value which is 10 times or more as large as the on resistance of the load transistor. 29. The shift register according to claim 16, wherein the control resistance has a resistance value which is ten times or more as large as the load resistance. 30. The shift register according to claim 17, wherein the control resistor has a resistance value which is 10 times or more as large as the on resistance of the load transistor.