JP6708037B2 - Image reading device and its reading drive circuit - Google Patents

Description

The present invention relates to a two-dimensional contact type image reading device and a reading drive circuit thereof.

The image reading device is a device that reads characters and images on a medium (hereinafter, also referred to as a document) on a read medium such as paper on which characters and images are written. As an apparatus for reading an image, there is also an apparatus for recognizing a character or an image read by an optical character reading apparatus (OCR), performing a predetermined process and displaying the character or the image (see Patent Documents 1, 2, and 3).

In recent years, a character recognition technique for image data has been developed, and language translation is possible by a technique such as the character recognition process and a syntax analysis. Generally, in the translation process, the manuscript image is read by a stationary image scanner, after performing preprocessing such as contour correction and contrast correction, if necessary, character recognition is performed, and then the steps of syntax analysis and translation are performed. ..

Similarly, a translation application or the like has been developed in which an image is acquired by a smartphone camera and the acquired image data and the translation result from the image data are simultaneously compared and displayed on the display of the smartphone. In this way, a portable input/output integrated device having both an image reading device capable of simultaneously confirming a manuscript and translation results and a display for displaying read image data and translation results is very useful. is there.

In recent years, with the development of high-speed communication networks, advanced processing such as image data preprocessing, character recognition, and parsing/translation can also be realized with cloud computing. It is also possible to utilize advanced learning functions by. A portable input/output integrated image reading device such as a smartphone or a tablet terminal that has a network interface and is in a communication environment may provide a high-quality translation service even if it does not have sophisticated processing or a large memory. it can.

However, smartphones, tablet terminals, etc. use cameras as reading devices, and during imaging, image blurring easily occurs due to vibrations such as focus shift and camera shake, and optimal exposure condition setting (aperture, shutter speed) for environmental illuminance. is necessary. In addition, when capturing an image of a document in an indoor environment, there is a problem in that the image captured by the camera is likely to cause a shadow of the image capturing apparatus itself or a reflection of illumination, which is a problem in that the recognition accuracy of characters and images is deteriorated and the ease of use is reduced. Spoil. Therefore, the photographer must photograph so that these conditions are met at a certain level.

Therefore, it has been proposed that these problems can be solved by forming a contact type fixed focus two-dimensional image reading device using a thin transistor in a thin sheet shape and combining it with a smartphone or a tablet terminal. The outline is shown in FIGS.

1A to 1E are schematic diagrams of an image reading device with a built-in smartphone case and a smartphone to which the smartphone case is attached. As shown in FIG. 1E, the image reading apparatus 101 includes an image reading unit 202 that reads a document, a light source unit 203 used when reading an image, and a control unit 201. The image reading unit 202 and the light source unit 203 are laminated, and the light source unit 203 is arranged between the image reading unit 202 and the smartphone case 212. When the image reading apparatus 101 is built in the smartphone case 212 as in the present embodiment, the image reading unit 202 exposes the reading surface to the outside of the smartphone case 212 on the surface opposite to the smartphone mounting surface. Is located in.

As shown in FIGS. 3(a) and 3(b), this apparatus can be placed on a medium to be read and imaged, and the above-mentioned problems of the camera reading can be solved. It is difficult to use a mechanical scanning mechanism or an optical focusing system in order to realize a thin sheet-shaped image reading apparatus. To solve this problem, it is useful to use the electronic scanning type transparent image reading device and the thin backlight shown in FIGS.

[Image reading method]
FIG. 4 shows a more detailed sectional structure of the image reading unit 202. Reference numeral 303 denotes a transparent thin substrate, and the light source unit 203 faces the medium to be read 204 with the image reading unit 202 interposed therebetween. The light receiving element 302 is formed on a transparent thin substrate 303. The side facing the medium to be read 204 is the light detection surface of the light receiving element 302. Reference numeral 301 denotes a transparent protective layer that is a part of the reading unit, and light 304 emitted from the light source unit 203 passes through the transparent substrate 303, passes through the gap of the light shield on the substrate including the light receiving element 302, After reaching the surface of the reading medium 204, reflected light 305 due to a drawing object on the surface of the medium to be read 204 is generated and enters the light receiving element 302 as detection light. This element structure in which the side opposite to the bonding surface between the light receiving element and the substrate is the light detecting surface is called the top reading type.

[Equivalent circuit of double-gate thin film transistor (DGTr)]
The light receiving element 302 shown in FIG. 4 is a DGTr, and its equivalent circuit diagram is shown in FIG. The DGTr is a four-terminal element, and in the top read type element, it is composed of a sense top gate terminal 410, a selection bottom gate terminal 413, and source or drain terminals 411 and 412. The attributes of the source and drain are determined by the relative potential.When the main carrier that constitutes the gate current is an electron, the terminal with a relatively negative potential serves as the source, and when the main carrier that constitutes the gate current is a hole, the relative The positive potential terminal becomes the source. The DGTr shown in FIG. 4 uses an amorphous SiTFT, the main carrier is an electron, and becomes an nch-type transistor.

[Structure of top read DGTr]
FIG. 6 illustrates the structure of the top reading DGTr of the top reading type reading unit. A sense top gate electrode 408 is provided on the substrate side so as to face the selective bottom gate electrode 401 with the a-Si semiconductor layer 403 forming the channel interposed therebetween. The interface region between the a-Si semiconductor layer 403 and the blocking layer insulating film 404 serves as a photosensitive portion where a negative electric field applied by the sense top gate electrode 408 is formed when the light receiving element is in the light detecting state. The interface region of the selective bottom gate insulating film 402 of the a-Si semiconductor layer 403 serves as a channel portion where a positive electric field applied from the selective bottom gate electrode 401 is formed when the light receiving element is in a data read state.

A source or drain electrode 406 is connected to the a-Si semiconductor layer 403 via an ohmic contact layer 405. The channel portion formed in the read state electrically connects the source and drain electrodes.

The sense top gate electrode 408, the transparent thin substrate 303, the selective bottom gate insulating film 402, the overcoat insulating film 407, the protective film 409, and the blocking layer insulating film 404 are transparent, the selective bottom gate electrode 401 is opaque, and the light source is The light incident from the portion 203 is incident on the photosensitive portion as the reflected light of the medium 204 to be read.

[Gate driver operation]
FIG. 7 shows a circuit diagram of a 3-row×3-column image sensor using a DGTr. Reference numeral 510 is a data driver, 520 is a selected bottom gate driver, 530 is a sense top gate driver, 540 is a data line, 541 is a selected bottom gate control line, 542 is a sense top gate control line, 543 is a source line, and 544 is a storage capacitance. Show.

The image sensor operates as described below. The image sensor has a selection bottom gate control line 541 and a sense top gate control line 542, and performs scanning in the same direction at different timings. The occupying time per row is the same for both the selection bottom gate control line 541 and the sense top gate control line 542, and this value is called a gate period.

The selected bottom gate control line 541 scans the matrix of the DGTFT sensor 550 from the first row to the third row for the on state (readout), and after turning on, sequentially shifts to the off state (holding). The sense top gate control line 542 scans the optical carrier sweeping (initialization state) from the first row to the third row with respect to the matrix of the DGTFT sensor 550, and after sweeping, sequentially shifts to the optical carrier accumulation.

FIG. 7 shows a state of the entire array in which the on (selection) scan of the selected bottom gate control line 541 is performed with a delay of two gate cycles from the sweep scan of the sense top gate control line 542. In this case, the scanning of the 3-row array sensor ends in a total of 5 gate cycles. This total gate period is called a scanning time. At this time, the light-receiving element 505 of the first row transits the accumulation state of a total of 2 gate cycles at the end of on-scanning, that is, the end of reading, and this total cycle is called an accumulation time. That is, the accumulation time and the scanning time of the sensor array in the scanning row n are d and the scanning time are n+d when the selective bottom gate scanning is started with a delay of d gate cycles after the start of the top sense gate scanning. The storage time is equal to the exposure time and the photo carriers accumulate during the storage state.

[Scan row state transition and detection principle]
8 to 10 are tables respectively showing details of the scanning row state transitions of the first to third rows of the 3×3 image sensor shown in FIG. 7. Further, FIGS. 11 to 15 are timing charts showing changes in potential of each control line in each gate cycle. Each scan row of the sensor array transits from gate state to gate state from 1 to 5. The state shown in FIG. 7 corresponds to the gate cycle 3. Each row is in the read state (the selected bottom gate control line is +15V: on) after the sweep state and the storage state have passed. There are subdivided read states. The potential of the storage capacitors is unified by passing through the discharge and precharge states, and then the data potential according to the accumulated optical carrier of each pixel is acquired through the natural discharge state. To do.

Next, the state transition and the detection principle will be described using a conceptual diagram of transistor operation.

FIG. 16 shows each part name in the transistor operation conceptual diagram. The select gate control line potential contributes to the generation of the channel 418 which is a current path between the source and the drain, and controls on at 15V and off at 0V. When the sense gate control line potential is −15V, the depletion layer 414 is generated, at the same time, the holes 415 are accumulated in the hole accumulation region 420, and the accumulated holes 415 are swept out at +15V.

The scan starts from the sweep state.

FIG. 17 shows a conceptual diagram of transistor operation in the sweep state. The potential of each control line in the sweep state changes as shown in FIG. 11 or 15. In the sweep state, +15V: sweep is applied to the sense top gate electrode 408, and 0V: off is applied to the selected bottom gate electrode 401. At this time, the positive electric field generated by +15 V applied to the sense top gate electrode 408 sweeps out the holes 415 remaining in the hole accumulation region 412 according to the history in advance. At this time, as shown in FIG. 17, an arbitrary potential is generated in the data line 540. After the sweep, it transits to the accumulation state.

FIG. 18 shows a conceptual diagram of dark transistor operation in the accumulated state, and FIG. 19 shows a conceptual diagram of bright transistor operation in the accumulated state. The potential of each control line in the storage state changes as shown in FIGS. In the storage state, −15 V: storage is applied to the sense top gate electrode 408, and 0 V: off is applied to the selection bottom gate electrode 401. At this time, the negative electric field generated by −15 V applied to the sense top gate electrode 408 excludes the electrons existing in the a-Si semiconductor layer 403 and generates a depletion layer hole 414.

As shown in FIG. 18, the depletion layer 414 reaches the channel region 416 in the dark pixel where light does not enter the light receiving unit 417. On the other hand, as shown in FIG. 19, in the bright portion pixel where the light 421 is incident on the light receiving portion 417, a hole-electron pair is generated in the a-Si semiconductor layer 403 by light irradiation, and a positive hole 415 having a positive charge is generated. Are accumulated in the hole accumulation region 420 by the negative electric field of −15 V of the sense top gate electrode 408. The positive electric charge of the accumulated holes 415 suppresses the negative electric field of −15 V of the sense top gate electrode 408, and the depletion layer 414 shrinks as compared with the dark pixel. That is, the degree of reduction of the depletion layer 414 is determined by the amount of accumulated holes depending on the light irradiation amount. At this time, as shown in FIGS. 18 and 19, an arbitrary potential is generated on the data line 540. After the accumulation state, the state shifts to the reading state.

The read state is subdivided into discharge, precharge, spontaneous discharge, and potential acquisition states.

In the discharged state and the precharged state, −15V: accumulation is applied to the sense top gate electrode 408, and 0V: off is applied to the selected bottom gate electrode 413. In the discharged state, a common voltage source is connected to all data terminals, and the potentials of all data lines are unified to 0V. Then, in the precharge state, a common voltage source is connected to all the data terminals, and the potentials of all the data lines are unified to 5V. After precharging, the data terminal 419 is set to high impedance (Hi-Z). Due to the charge stored in the storage capacitor 544, a potential difference of 5 V remains between the source line 543 and the data line 540. Following precharge, the read state transitions to the spontaneous discharge state and the potential acquisition state.

FIG. 20 is a conceptual diagram of transistor operation of the dark pixel in the natural discharge state and potential acquisition state, and FIG. 21 is a conceptual diagram of transistor operation of the bright pixel in the natural discharge state and potential acquisition state. In the spontaneous discharge state and the potential acquisition state, −15 V: accumulation is applied to the sense top gate electrode 408, and +15 V: on is applied to the selected bottom gate electrode 413. The +15V of the selected bottom gate electrode 413 generates a channel in the channel forming portion 418 which serves as a current path between the source/drain 406.

As shown in FIG. 20, hole accumulation does not occur in the dark pixel where light does not enter the light receiving unit 417, the depletion layer 414 reaches the channel region 416, and blocks the channel formed by the selective bottom gate 413. Therefore, discharge does not occur in the dark pixel in the natural discharge state, and 5 V precharged in the storage capacitor 544 is maintained until the potential acquisition state. On the other hand, as shown in FIG. 21, in the bright pixel where the light 421 is incident on the light receiving section 417, holes 415 are accumulated according to the integrated exposure amount, and the depletion layer 414 is reduced according to the integrated light irradiation amount. is doing. The amount of current flowing through the channel generated by +15V:on applied to the selective bottom gate 413 changes depending on the size of the depletion layer 414. A pixel having a large integrated exposure amount and a smaller depletion layer 414 has a larger current driving capability. Therefore, in the bright pixel in the natural discharge state, discharge corresponding to the integrated exposure amount occurs, and 5V precharged in the storage capacitor 544 decreases toward the potential 0V of the source line 543.

In the potential acquisition state following the natural discharge, the data terminal 419 is connected to the analog-digital converter in the driver 510 to acquire the voltage of the data line 540 during the discharge process. Therefore, in a pixel having a large integrated exposure amount and a larger current driving capability, faster discharge occurs and a lower potential is acquired.

FIG. 22 shows an outline of a pixel circuit and a driving method in the conventional 3 column data×3 row scanning using natural discharge for data reading. Further, FIG. 23 shows an outline of the data line operation at the time of reading the conventional data, and FIG. 24 shows the voltage change of the data line at the time of reading the data and the data acquisition timing in the conventional driving method.

The sweep state and the storage state are controlled by the sense top gate driver 630 via the sense top gate control line 642, and the on/off states in the read state are controlled by the selected bottom gate driver 620 via the selected bottom gate control line 641. To do. The discharge state and the precharge state are controlled by turning on the switch 611 of the data driver 610 and switching the switch 612. When +15V is applied to the selected bottom gate control line 641 to turn on the read state, the switch 611 is turned off at the same time, and the state transits to the spontaneous discharge state and the potential acquisition state in order. The measured potential is detected as the voltage across the storage capacitor 644, that is, the potential difference between the source and drain.

[Types of electronic scanning transparent image reading device]
Examples of the electronic scanning transparent image reading device include a device that electronically scans a CMOS image sensor type pixel circuit using a polycrystalline Si thin film transistor (polySiTFT) technology, and a double gate thin film transistor (a-SiTFT) using an amorphous Si thin film transistor (a-SiTFT) There is a device for electronically scanning a DGTr). The a-Si TFT is mass-produced for a large-sized TV and is advantageous for realizing a contact type two-dimensional image reading device having a larger area. Further, the DGTr type has a simpler pixel circuit and has a higher aperture ratio than the polySiTFT type, and is advantageous for high sensitivity and miniaturization.

JP, 2003-8843, A Japanese Patent No. 3234736 Japanese Patent No. 2735697

In the conventional electronic scanning image reading apparatus described so far, the scanning time increases due to the increase in the number of scanning lines due to the increase in the area and the increase in the time constant due to the increase in the wiring resistance and the parasitic capacitance. However, shorter scanning times are preferred for users of image reading devices. In order to suppress the scanning time, it is necessary to shorten the scanning gate cycle. As shown in FIG. 13, in the conventional DGTr type drive in which the data line potential is obtained by natural discharge, the length of the gate cycle mainly depends on the natural discharge period. The speed of spontaneous discharge depends on the current driving capability of the transistor. As shown in FIG. 21, in the conventional driving method, the driving capability of the transistor depends on the potential difference between the data line 540 and the source line 543. In the natural discharge, this potential difference is gradually reduced until the data is acquired as shown in FIG. 24, that is, the discharge speed is reduced, which is not preferable for shortening the gate cycle.

The present invention has been made in view of such problems, and an object thereof is to obtain data at a higher speed in an image sensor system using a tabletable gate TFT as compared with a conventional method using natural discharge. An object of the present invention is to provide an image reading device that realizes the above and a reading drive circuit thereof.

In order to solve the above-mentioned problems, the present invention is a read drive circuit for reading an imaged data value of an image reading device having a double gate TFT as an image pickup element, wherein a drain terminal of the double gate TFT is connected via a data line. Connected voltage measuring means, which outputs a measured value of a transient voltage or a saturation voltage on the data line that changes depending on the driving ability according to the exposure amount of the double gate TFT, A constant current source connected to the data line in parallel with the voltage measuring means, wherein the constant current source applies a predetermined inrush current to the drain terminal of the double gate TFT via the data line, It is characterized by having.

According to a second aspect of the present invention, there is provided a two-dimensional image reading apparatus having a double gate TFT as an image pickup device, wherein a plurality of the double gate TFTs are two-dimensionally arranged in a TFT array and a drain terminal of the double gate TFT. A voltage measuring means connected via a data line, which outputs a measured value of a transient voltage or a saturation voltage on the data line, which changes depending on a driving ability according to an exposure amount of the double gate TFT. A constant current source connected to the voltage measuring means and the data line in parallel with the voltage measuring means, wherein a predetermined inrush current is applied to the drain terminal of the double gate TFT via the data line, A read drive circuit having a constant current source, a select bottom gate drive circuit connected to a bottom gate terminal of each double gate TFT of the TFT array via a select bottom gate control line, and each double gate TFT of the TFT array And a sense top gate drive circuit connected to the top gate terminal via a sense top gate control line.

The invention according to claim 3 is a two-dimensional image reading apparatus using a double gate TFT as an image pickup device, wherein the double gate TFT has a diode connection structure in which one of a bottom gate terminal and one of a source/drain electrode is short-circuited. And a voltage measuring means connected to a cathode terminal of each diode-connected double-gate TFT of the TFT array via a data line, in which a plurality of two-dimensionally arranged TFT arrays are arranged. And a constant current source connected to the data line in parallel with the voltage measuring unit, which outputs a measured value of a transient voltage or a saturation voltage on the data line that changes depending on the driving capability. And a read drive circuit including the constant current source for drawing a predetermined drawing current to the cathode terminal of the double gate TFT through the data line, and the anode terminal and the bottom gate of each double gate TFT of the TFT array. A select bottom gate drive circuit connected to the terminal via a select bottom gate control line; and a sense top gate drive circuit connected to the top gate terminal of each double gate TFT of the TFT array via a sense top gate control line. , Is provided.

According to a fourth aspect of the present invention, in the two-dimensional contact image reading apparatus according to the second or third aspect, the constant current source is formed by a TFT circuit.

INDUSTRIAL APPLICABILITY The present invention has the effect of suppressing an increase in scanning time due to an increase in size and an increase in the number of scanning lines in a two-dimensional contact type image sensor system using a DGTr.

(A) is a schematic view of a smartphone or a tablet PC case in which the image reading device according to the first embodiment of the present invention is built-in, in a state where the smartphone or the tablet PC case is not mounted, as viewed from the fitting portion side, 2B is a schematic view of the image reading apparatus according to the first embodiment of the present invention viewed from the image reading side, FIG. 7C is a schematic view of a smartphone or a tablet PC, and FIG. Is a schematic view seen from the display side of the smartphone or the tablet PC, in which the smartphone or the tablet PC case having the built-in image reading device according to the embodiment is fitted to the smartphone or the tablet PC. 3 is a sectional view taken along line AA′ of FIG. (A) It is the schematic diagram seen from the light source part side of the image reading device concerning the 1st embodiment of the present invention, (b) is the side view, and (c) is the outline figure seen from the reading part side. It is a figure. (A) is a figure which shows the state which the image reading apparatus which concerns on the 1st Embodiment of this invention is reading the image on a to-be-read medium, (b) is an AA' cross section figure of (a). .. It is a detailed sectional view of a top reading type reading unit. It is an equivalent circuit diagram of a double gate transistor which is an example of a light receiving element. It is a figure which shows the detailed structure of the top reading light receiving element of a top reading type reading part. It is a schematic circuit diagram of an image sensor of 3 rows x 3 columns using DGTr. 8 is a table summarizing details of state transitions in the first row of the 3×3 image sensor in FIG. 7. 8 is a table summarizing details of state transitions of a second row of the image sensor of 3 rows×3 columns in FIG. 7. 8 is a table summarizing details of state transitions of a third row of the image sensor of 3 rows×3 columns in FIG. 7. It is a figure which shows the change of the electric potential of each control line and a data line in the gate period of a sweep state and a non-reading state. FIG. 6 is a diagram showing changes in potentials of control lines and data lines in a gate cycle in a storage state and a non-reading state. It is a figure which shows the change of the electric potential of each control line and a data line in the gate period of the reading state of the row whose selection bottom gate control lines are +15V:on. It is a figure which shows the change of the electric potential of each control line and the data line in the gate period of the reading state of the row whose selection bottom gate control lines are 0V:off. It is a figure which shows the change of the electric potential of each control line and a data line in the gate period of a sweep state and a read state. It is a figure explaining a pixel transistor operation concept. It is a figure which shows the pixel transistor operation concept in a sweep state. It is a figure which shows the transistor operation concept of an accumulation state dark part pixel. It is a figure which shows the transistor operation concept of an accumulation state dark part pixel. It is a figure which shows the transistor operation concept of a read/spontaneous discharge or potential acquisition state dark part pixel. It is a figure which shows the transistor operation concept of reading/spontaneous discharge or electric potential acquisition state bright part pixel. It is a figure which shows the outline of the conventional pixel circuit in 3 column data x 3 row scanning, and a driving method. It is a figure which shows the outline of the data line operation|movement at the time of the conventional data read. It is a figure which shows the voltage change of the data line at the time of data read in the conventional drive method, and data read timing. FIG. 3 is a diagram showing an outline of a pixel circuit in 3 column data×3 row scanning and a high-speed read driving method according to the first embodiment of the present invention. It is a figure which shows the outline|summary of the data line operation|movement at the time of the data read concerning 1st Embodiment of this invention. It is a figure which shows the Vds-Id characteristic of a DGTFT sensor. FIG. 5 is a diagram showing a voltage change of a data line and a data read timing at the time of reading data in the driving method according to the first embodiment of the present invention. It is a figure which shows the outline|summary of the pixel circuit in 3 column data x 3 row scanning and the high-speed read-out drive method which concern on 2nd Embodiment of this invention. It is a figure which shows the outline of the data line operation|movement at the time of the data read concerning 2nd Embodiment of this invention. It is a figure which shows the VI characteristic of the DGTFT sensor which carried out the diode connection. It is a figure which shows the voltage change of the data line at the time of the data read and the data read timing in the driving method which concerns on 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail.

<First Embodiment>
FIG. 25 shows an outline of a pixel circuit in 3 column data×3 row scanning and a high-speed read driving method according to the first embodiment of the present invention, and FIG. 26 shows a data read operation according to the first embodiment of the present invention. An outline of the data line operation of is shown. Further, FIG. 27 shows the Vds-Id characteristics of the DGTFT sensor, and FIG. 28 shows the voltage change of the data line at the time of data reading and the data reading timing in the driving method according to the first embodiment of the present invention.

Each DGTFT sensor 750, selective bottom gate driver 720, and sense top gate driver 730 in the pixel circuit shown in FIG. 25 have the same structure and driving method as the conventional one. That is, the data driver 710 is connected to the drain terminal of each DGT TFT sensor 750 via the data line 740, and the source terminal is connected to the ground via the source line 743. The selected bottom gate terminal of each DGT TFT sensor 750 is connected to a selected bottom gate driver 720 via a selected bottom gate control line 741, and the sense top gate is connected to a sense top gate control line 742 via a sense top gate driver 730. Are connected. The selected bottom gate driver 720 has +15V when turned on and 0V when turned off, and the sense top gate driver 730 has +15V when swept and -15V when accumulated.

On the other hand, the configuration of the data driver 710 is different from the conventional one. In the data driver 710, a push constant current source 713 is connected to the data line 740 in parallel with an AD converter 712 that measures the voltage of the data line 740, and the constant current push voltage upper limit of the push constant current source 713 is 15V. To do. Thus, as shown in FIG. 26, the measured potential is detected as the voltage across the storage capacitor 744, that is, the potential difference between the source and the drain, as in the conventional case.

Immediately before applying +15V to the selected bottom gate control line 741 to turn it on, the switch 711 is turned on and discharged to adjust the potential of the data line 740 to 0V, then the switch 711 is turned off, and then the switch 714 is turned on. Then, the constant current source 713 is connected to the data line 740 side to push in the current. At this time, the voltage Vds of the data line 740 with respect to the source line 743 becomes a voltage corresponding to the inrush current value according to the drive capability characteristics of the transistor according to the exposure amount shown in FIG. That is, as shown in FIG. 28, the data line potential is quickly saturated toward a value determined by the driving ability characteristic of the transistor and the inrush current value according to the exposure amount. At this time, the rate of voltage change is proportional to the inrush current. The AD converter 712 uses the transient voltage or the saturation voltage of the data line 740 after a predetermined time elapses after the selection bottom gate is turned on and the current inrush is started via the DGTFT sensor 750, as the imaging data value of the DGTFT sensor 750. taking measurement.

In the present embodiment, the constant current source 713 provided in the data driver LSI may be formed together with the DGTFT by a TFT circuit.

[Effects of First Embodiment]
According to this embodiment, the following effects are achieved.

In the conventional natural discharge, the voltage of the data line 740 gradually decreases toward 0V while decreasing the discharge rate according to the potential of the storage capacitor, because the discharge current decreases according to the potential of the storage capacitor. To go. On the other hand, in the present embodiment, by applying a predetermined inrush current using the constant current source 713, as shown in FIG. 27, the source-drain voltage Vsd according to the transistor driving capability according to the exposure amount at the predetermined inrush current amount. Can be saturated quickly. Therefore, in a two-dimensional electronic scanning type image reading apparatus using a DG-TFT sensor, higher speed data acquisition is realized as compared with the conventional driving method, and an increase in scanning time due to an increase in sensor panel size is suppressed. You can

In this embodiment, the constant current source provided in the data driver LSI may be formed together with the DGTFT by a TFT circuit.

<Second Embodiment>
FIG. 29 shows an outline of a pixel circuit in 3 column data×3 row scanning and a high-speed read driving method according to the second embodiment of the present invention, and FIG. 30 shows a data read operation according to the second embodiment of the present invention. An outline of the data line operation of is shown. Further, FIG. 31 shows the VI characteristics of the diode-connected DGTFT sensor, and FIG. 32 shows the voltage change of the data line at the time of data read and the data read timing in the driving method according to the second embodiment of the present invention. Show.

The second embodiment differs from the first embodiment in the configuration of the data driver 810 and the DGTFT sensor 850 and the set voltage when the selection bottom gate driver 820 is turned on/off. As shown in FIGS. 29 and 30, in the driving method of this embodiment, each DGTFT 850 has a diode connection structure in which one of the selection bottom gate electrode and one of the source/drain electrodes are short-circuited. In the second embodiment, since data is read by the pull-in constant current source 813 in the data driver 810, the electrode connected to the data line of the DGTFT 850 source/drain terminal has a relatively negative potential, that is, the source terminal. Since one drain terminal is diode-connected short-circuited with the selected bottom gate electrode, the source terminal may be called the cathode terminal and the drain terminal may be called the anode terminal. Therefore, there is no independent source line in this embodiment. Further, a storage capacitor 843 is connected between the selected bottom gate control line 841 and the data line 840.

In the data driver 810, a pull-in constant current source 813 is connected to the data line 840 in parallel with the AD converter 812, and the constant current pull-in voltage lower limit of the pull-in constant current source 813 is −15V. The select bottom gate driver 820 has 0 V when it is on, and -15 V when it is off, and the sense top gate driver 830 has +15 V when sweeping and -15 V when accumulating.

Immediately before applying 0V to the selected bottom gate control line 841 to turn it on, the switch 811 is turned on and precharged to adjust the potential of the data line 840 to 0V, then the switch 811 is turned off, and then the switch 814 is turned on. When turned on, the constant current source 813 is connected to the data line 840 side to draw a current. At this time, the voltage V of the data line 840 with respect to the anode of the DGTFT 850 to which 0V is applied via the selective bottom gate control line 841 is shown in FIG. 32 according to the driving capability characteristic of the transistor diode connection according to the exposure amount shown in FIG. As shown, it quickly approaches saturation. The AD converter 812 uses the transient voltage or the saturation voltage of the data line 840 after a lapse of a predetermined time after the selection bottom gate is turned on and the current drawing is started via the DGTFT sensor 850, as the imaging data value of the DGTFT sensor 850. taking measurement.

Incidentally, in this embodiment, the constant current source 813 provided in the data driver LSI may be formed together with the DGTFT by a TFT circuit.

[Effects of Second Embodiment]
According to this embodiment, the following effects are achieved.

The speed of saturation depends on the time constant due to the parasitic capacitance connected to each data line 840 and the wiring resistance, and the magnitude of the current drawn by the constant current source 813. Even when the scan time increases with the increase in size and the number of scan lines, the pull-in current is increased and the time to reach saturation is shortened, whereby the increase in read time can be suppressed.

In a two-dimensional electronic scanning type image reading device using a DG-TFT sensor, higher-speed data reading can be realized as compared with the conventional driving method, and an increase in scanning time due to an increase in sensor panel size can be suppressed. it can. Further, since each DGTFT sensor has a diode connection, the source line in the conventional circuit is not required, so that the aperture ratio and the sensor area can be increased, and the manufacturing yield is improved.

Although the embodiments of the present invention have been described above in detail, the present invention is not limited to the above-described embodiments in practice, and modifications within the scope of the present invention are included in the present invention.

101 image reading device 201 control unit 202 image reading unit 203 light source unit 204 medium to be read 205 TFT area switching circuit 206 TFT area switching control line 207 sensor array area 209 display unit 211 mobile terminal such as smartphone or tablet PC 212 smartphone or tablet PC case 213 Discharge by TFT, precharge, unconnected 3-state switching circuit 214 TFT state switching circuit control line 214-1 Data line connection/non-connection (high impedance: Hi-z) control line 214-2 Discharge control line 214-3 Precharge control line 301 Transparent protective layer 302 Light receiving element 302a Light receiving element Reading/detecting state 302b Light receiving element non-reading/detecting state 302c Light receiving element non-reading/initialization state 303 Transparent thin substrate 304 Light source emitted light 305 Medium reflected light 401 bottom gate electrode 402 bottom gate insulating film 403 semiconductor layer 404 blocking layer insulating film 405 ohmic contact layer 406, 411, 412 source or drain electrode 407 overcoat insulating film 408 top gate electrode 409 protective film 410 top gate terminal 413 bottom gate terminal 414 Depletion layer 415 Hole 416 Electron 417 Light receiving part 418 Channel region 419 Data terminal (driver input/output terminal)
420 hole accumulation region 421 pixel incident light 510, 610, 710, 810 data driver 520, 620, 720, 820 selective bottom gate driver 530, 630, 730, 830 sense top gate driver 540, 640, 740, 840 data line 541 , 641, 741, 841 Selective bottom gate control lines 542, 642, 742, 842 Sense top gate control lines 543, 643, 743, 843 Source lines 544, 644, 744, 844 Storage capacitors 550, 650, 750, 850 DGTFT sensor 611, 612, 711, 811, 714, 814 Switch 613, 712, 812 AD converter 713, 813 Constant current source

Claims (4)

A reading drive circuit for reading an imaged data value of an image reading device using a double gate TFT as an image pickup element,
A voltage measuring unit connected to a drain terminal of the double gate TFT via a data line, the transient voltage or the saturation voltage on the data line changing depending on the driving ability according to the exposure amount of the double gate TFT. Outputting the measured value of the voltage measuring means,
A constant current source connected to the data line in parallel with the voltage measuring means, for applying a predetermined inrush current to the drain terminal of the double gate TFT via the data line,
A read drive circuit comprising: A two-dimensional image reading device using a double gate TFT as an image pickup element,
A TFT array in which a plurality of the double gate TFTs are two-dimensionally arranged,
A voltage measuring unit connected to a drain terminal of the double gate TFT via a data line, the transient voltage or the saturation voltage on the data line changing depending on the driving ability according to the exposure amount of the double gate TFT. A constant current source for outputting the measured value of the voltage measuring means and a constant current source connected in parallel to the voltage measuring means on the data line, the drain terminal of the double gate TFT being predetermined through the data line. And a read drive circuit including the constant current source, for applying the inrush current of
A select bottom gate drive circuit connected to a bottom gate terminal of each double gate TFT of the TFT array via a select bottom gate control line;
A sense top gate drive circuit connected to the top gate terminal of each double gate TFT of the TFT array via a sense top gate control line;
An image reading apparatus comprising: A two-dimensional image reading device using a double gate TFT as an image pickup element,
A TFT array in which a plurality of the double gate TFTs having a diode connection structure in which one of a bottom gate terminal and one of a source/drain electrode is short-circuited are arranged two-dimensionally
Voltage measuring means connected to the cathode terminal of each diode-connected double-gate TFT of the TFT array via a data line, wherein the data changes depending on the driving capacity according to the exposure amount of the double-gate TFT. A constant current source for outputting a measured value of a transient voltage or a saturation voltage on a line, the constant voltage source being connected to the data line in parallel with the voltage measuring unit, the cathode terminal of the double-gate TFT. A read driving circuit including the constant current source, which draws a predetermined drawing current through the data line;
A selection bottom gate drive circuit connected to the anode terminal and bottom gate terminal of each double gate TFT of the TFT array via a selection bottom gate control line;
A sense top gate drive circuit connected to the top gate terminal of each double gate TFT of the TFT array via a sense top gate control line;
An image reading apparatus comprising: The two-dimensional contact image reading apparatus according to claim 2, wherein the constant current source is formed by a TFT circuit.

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