JPH09230307A - Active matrix type liquid crystal display - Google Patents

Abstract

The present invention relates to an active matrix liquid crystal display device having an image reading function, and an object thereof is to improve noise resistance during image reading. A photodiode 25 has a cathode side connected to a pixel electrode 23 and an anode side connected to the previous gate electrode 22, and writing to the pixel electrode 23 via a transistor T _r at the time of pixel reading. After the predetermined scanning period, the potential of the pixel electrode 23 is read through the transistor T _r and compared to identify the light detection state of the photodiode 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device having an image reading function. 2. Description of the Related Art In recent years, active matrix type liquid crystal display devices have characteristics of thinness, light weight, low power consumption and high image quality display, and those mounted on notebook type personal computers and the like have become widespread. In such a liquid crystal display device, improvement in convenience is desired, and high functionality with various additional functions is desired. As one of them, there is an active matrix type liquid crystal display device having an image reading function, and improvement of reading quality is required.

[0002]

2. Description of the Related Art Conventionally, when an image such as a chart or the like is to be captured when a sentence is created on a personal computer, for example, a scanner device is externally connected and the chart or the like is read by the scanner device. . However, since the size of the device becomes large, it is considered that the liquid crystal panel of the liquid crystal display device has an image reading (scanner) function, as disclosed in JP-A-5-281516, JP-A-6-22250, and JP-A-6-25016. What is described in Japanese Patent No. 186585 is known.

Here, FIG. 8 shows a circuit configuration diagram of a main part of a conventional image reading liquid crystal display device. FIG. 8 shows only one pixel of the liquid crystal panel in the active matrix type liquid crystal display device, and the data bus line 11 and the scan bus line 12 are arranged in a grid pattern so that one frame is one pixel. The data bus line 11 has a transistor T
The drain (or source) of _r1 is connected, and the scan bus line 12 is connected to the gate of the transistor T _r1 . The source (or drain) of the transistor T _r1 is connected to the pixel electrode 13. Liquid crystal is sandwiched between the pixel electrode 13 and a counter electrode (not shown).

The data bus line 11 is connected to the drain (or source) of the transistor T _r2 , and the scan bus line 12 is connected to the gate of the transistor T _r2 . The source (or drain) of the transistor T _r2 is connected to the cathode of the photodiode 14, and the anode of the photodiode 14 is connected to the common electrode (or auxiliary electrode) 15.

The transistor T _r1 is for driving the pixel electrode 13 for liquid crystal display, and the transistor T _r2 is for driving the photodiode 14 for reading an image. A liquid crystal panel having an image reading function is constructed by arranging such pixels in a matrix.

Therefore, at the time of image reading, a photocurrent flows due to the photodetection of the photodiode 14 of each pixel according to the document, and the photocurrent is taken out from the transistor T _r2 to read the image. In this case, the photocurrent of each photodiode is taken out to the outside in real time during image reading.

[0007]

However, as described above, when the photodiode 14 is driven by the transistor _Tr2 to take out the photocurrent to the outside in real time, the photocurrent of the photodiode 14 is 10 ^-9 -10. ^Since it is ^-10 A, there is a problem that the SN ratio is low and it is easily affected by external noise.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide an active matrix type liquid crystal display device capable of improving noise resistance during image reading.

[0009]

In order to solve the above-mentioned problems, according to a first aspect of the present invention, a pixel in which a predetermined number of scan bus lines and data bus lines are arranged in a grid pattern and a liquid crystal is sandwiched in a surrounded portion. In an active matrix type liquid crystal display device, in which electrodes and counter electrodes are arranged in a matrix, and driving means for driving the pixel electrodes in response to signals from the scan bus lines and data bus lines, one end of the pixel A light detection unit that is connected to an electrode and has the other end connected to a constant voltage portion to detect light is provided. When the image is read, the driving unit causes the pixel electrode to write, and after a predetermined scanning period, the pixel electrode An active matrix type liquid crystal display device having a control means for discriminating the light detection of the light detection means by a potential is constructed.

According to a second aspect of the present invention, in the light detecting means according to the first aspect, one end of the cathode side is connected to the pixel electrode, and the other end of the anode side is connected to the scan bus line immediately before the corresponding scan bus line. It will be done. According to a third aspect of the present invention, in the light detecting means of the first aspect, one end has a cathode side connected to the pixel electrode, and the other end has an anode side connected to an auxiliary electrode having a potential lower than that of the pixel electrode.

According to a fourth aspect of the present invention, in the light detecting means according to the first aspect, one end has an anode side connected to the pixel electrode and the other end has a cathode side connected to an auxiliary electrode having a higher potential than the pixel electrode. According to a fifth aspect, the drive means according to the first aspect has a bidirectional function of writing and reading with respect to the pixel electrode.

According to a sixth aspect of the present invention, the control means according to the first aspect comprises a data supply means for supplying a data voltage at the time of writing to the pixel electrode, and a determination means for reading and comparing the potential of the pixel electrode at the time of reading. And a switching unit that switches between the data supply unit and the determination unit.

In a seventh aspect, the control means according to the first or sixth aspect causes the reading of the pixel electrode to be performed after a scanning period of a predetermined number of frames after the writing. Claim 8
Then, in any one of claims 1, 6 and 7, a light irradiation means is provided at the time of displaying by the liquid crystal, and the brightness by the light irradiation means is increased at the time of writing to the pixel electrode during image reading. It becomes.

As described above, in the invention of claim 1, 2, 3, 4, 6 or 7, one end of the light detecting means is connected to the pixel electrode and the other end is in a reverse bias state with the pixel electrode when no light is detected. In this state, the potential of the pixel electrode is changed in the light detection state of the light detection unit by the control unit causing the data supply unit to write to the pixel electrode during image reading, For example, after a scanning period of a predetermined number of frames, the switching unit switches the pixel electrode to read the potential of the pixel electrode, and the light detection of the light detection unit is identified by the determination unit. As a result, since the potential of the pixel electrode is read out after a predetermined period, the influence of external noise on the light detection by the light detection unit is avoided, and the noise resistance can be improved.

According to the invention of claim 5, the driving means is provided with a bidirectional function. As a result, it becomes possible to write and read to the pixel electrode singly. According to the invention of claim 8, a light irradiating means for irradiating light at the time of liquid crystal display is provided, and the brightness is increased by the light irradiating means at the time of writing the pixel electrode for image reading. This makes it possible to further improve noise resistance.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circuit configuration diagram of a main part of an embodiment of the present invention. FIG. 1 shows only one pixel of a liquid crystal panel in an active matrix liquid crystal display device according to the present invention. A drain electrode (or a source electrode may be used) 21 as a data bus line and a gate electrode 22 as a scan bus line. Are arranged orthogonally in a grid pattern. The portion surrounded by these becomes one pixel as shown in FIG. 1, and the pixel electrode 23 (described in FIG. 2) and the counter electrode 24 are arranged so as to sandwich the liquid crystal therebetween. A liquid crystal capacitance is provided between the pixel electrode 23 and the counter electrode 24.

Meanwhile, the gate electrode (gate (n)) 22 is the gate of the transistor T _r, for example, n-type by TFT (Thin Film Transistor) as a driving means is connected,
The drain (or source) of the transistor T _r
Is connected to the drain electrode 21. The source of the transistor T _r (or drain) is connected to the pixel electrode 23.

Further, the cathode at one end of a photodiode 25 which is a light detecting means is connected to the pixel electrode 23. Then, the anode at the other end of the photodiode 25 is connected to the gate electrode (gate (n-1)) 22 one before. One pixel configured in this way is the drain electrode 2
1 to form an active matrix type arrayed in a portion surrounded by 1 and the gate electrode 22.

Here, FIG. 2 shows an internal configuration diagram of FIG. 2A shows a portion of the liquid crystal panel corresponding to FIG. 1, FIG. 2B shows a sectional view of the photodiode 25 portion (AA sectional view), and FIG. 2C shows a transistor _Tr. The sectional view (BB sectional drawing) of a part is shown. As shown in FIG. 2A, a pixel electrode 23 is arranged in a portion where the drain electrode 21 and the gate electrode 22 are intersected and surrounded, and the pixel electrode 23 is disposed between the pixel electrode 23 and the drain electrode 21 and the gate electrode 22. A transistor T _r and a photodiode 25 as shown in FIG. 1 are formed.

As shown in FIG. 2 (B), the photodiode 25 has a glass substrate 31 on which T _i is formed as an anode electrode.
(Titanium) layer 32 is formed, the amorphous silicon layer 3 is amorphous silicon in some contact with the said T _i layer 32
3 is formed. The T _i layer 32 is formed integrally with the gate electrode 22. Further, an n ⁺ amorphous silicon layer 34 is formed on a part of the amorphous silicon layer 33, and a transparent ITO (indium tin oxide) pixel electrode 23 is formed on the glass substrate 31 over the n ⁺ amorphous silicon layer 34. To be done.

A transparent ITO counter electrode 24 formed on a glass substrate 35 is arranged above the pixel electrode 23, and a liquid crystal 36 is sandwiched between the pixel electrode 23 and the counter electrode 24. The transistor T _r, as shown in FIG. 2 (C), the gate electrode layer 37 integral with the gate electrode 22 on the glass substrate 31 is formed, the insulating layer 38 is formed on the gate electrode layer 37 . An amorphous silicon layer 39 is formed on the insulating layer 38, and the amorphous silicon layer 39 is formed.
N ⁺ amorphous silicon layer 40 _a , 4 divided above
0 _b is formed. Then, the drain layer 41 _a and the source layer 41 _b are formed on the n ⁺ amorphous silicon layers 40 _a and 40 _b , respectively. The drain layer 41 _a is formed integrally with the drain electrode 21, and the ITO is formed on the source layer 41 _b.
The pixel electrode 23 of is formed.

An ITO counter electrode 24 formed on a glass substrate 35 is disposed above the pixel electrode 23, and a liquid crystal 36 is sandwiched between the pixel electrode 23 and the counter electrode 24. 2A to 2C are formed in a matrix on the glass substrate 31 to form the liquid crystal panel 42.

As described above, the T _i layer 32 of the photodiode 25 can be formed by using the material of the gate electrode 22 as it is, and the amorphous silicon layer 33 and the n ⁺ amorphous silicon layer 34 can be formed at the same time when the transistor T _r is formed. Therefore, the manufacturing process can be reduced and the cost can be reduced.

Next, FIG. 3 shows an explanatory diagram of the operating principle of the photodiode of FIG. As shown in FIG.
The photodiode 25 is equivalently represented by a parallel circuit of _a capacitor _25a and a current source _25b (current flows from the cathode side). In this case, the current source 25 _b has a photocurrent I _p and a dark current (current that flows even without light irradiation) I.
_The current (I _p + I _d ) added by _d flows from the cathode side to the anode side. For example, when 10 μm □ is irradiated with light of several thousand l _x , photocurrent flows to 10 ⁻¹⁰ A,
The dark current I _{d in} this case is 10 ⁻¹² A. That is,
If the photodiode 25 is not irradiated with light, the dark current I _d is flowing from the cathode side to the anode side, and if the predetermined amount of light is irradiated, the cathode side to the anode side I _p.
A current of + I _d flows.

Therefore, when the image of the original is read, the photodiode 25 is illuminated by the contents of the original.
Then, the photodiode 25 which is not irradiated with light is generated.
In this case, when the pixel electrode 23 is driven by the transistor T _r of a predetermined potential, photo when not irradiated with light to the diode 25 (nontransparent state light image described in the document of the pixel electrode 23 ), The pixel electrode 23
The potential of is roughly maintained (dark current shall be ignored). On the other hand, when the photodiode 25 is irradiated with light (transmission state corresponding to a portion where nothing is written on the document), the photodiode 25 receives a photocurrent I _p.
(Actually, I _p + I _d ) flows and the potential of the pixel electrode 23 decreases.

That is, as shown in FIG.
Electrode 23 is transistor T_rThe potential due to writing is 1
At 0 [V], the photodiode 25 is illuminated with light.
The potential of the pixel electrode 23 decreases with the passage of time
I will do it. Then, the photodiode 25 is irradiated with light.
After a predetermined time, the electric potentials of the pixel electrodes 23 are compared.
Then, the photodiode 25 is not affected by external noise.
It is possible to identify whether or not the light is detected. For example,
After the light irradiation is disclosed in the photodiode 25,
One frame interval t₁(16.7 ms) period
Potential difference after passing V _dIs above the specified value, the photodio
That is distinguished from that detected by the light transmitted by the document 25
It is.

Therefore, FIG. 4 shows a conceptual diagram of document reading according to the present invention. In an active matrix type liquid crystal display 51 having an image reading function according to the present invention, a backlight 53 as a light irradiating means is arranged below the liquid crystal panel 42, and a semitransparent original 53 is provided between the backlight 52 and the liquid crystal panel 42. Is set so that the light corresponding to the black-and-white screen (or color screen) of the document is applied to the photodiode 25 of the liquid crystal panel 42.

Next, FIG. 5 shows a configuration diagram of writing to the pixel electrodes when reading an original. FIG. 5A is a block diagram for realizing the image reading function of the active matrix liquid crystal display device 51. Serial write data is input to the serial / parallel conversion unit 61 and converted into parallel data. Sent. Latch 62
Sends the output for each data bus line (drain electrode) 21 to the write terminal of each analog switch 63 of the switch group corresponding to the corresponding switching means. The common terminal of each analog switch 63 is a liquid crystal display panel (LCD) 4
2 is connected to each data bus line (each drain electrode) 21 and shows write data or read data.

When read data appears at the read terminal of each analog switch 63, the latch 64 holds the read data, the comparator 65 determines whether the photodiode 25 detects light, and the interface 66 performs parallel-Syrian conversion. Then, the data is output to, for example, a personal computer as a host device.

The serial / parallel converter 61 and the latch 62 constitute a data supply means, and the latch 64 and the comparator 65 constitute a discrimination means.
These and each analog switch 63 constitute a control means. Each analog switch 63 is switched by a control signal from the personal computer input through the interface 66.

Therefore, in FIG. 5A, writing is performed in each pixel electrode 23 at the time of reading an original, and each analog switch 63 is controlled to the writing terminal side. The serial write data that is input is converted to parallel by the serial-parallel converter 61 and latched by the latch 62, and each data bus line (drain electrode) 2 of the liquid crystal panel 42 is passed through each analog switch 63.
1 is supplied. Then, by scanning the scan bus line (gate electrode) 22 line by line, a data potential of, for example, 10 V as shown in FIG. 3B is applied to the entire surface of each pixel electrode 23.

For example, when the scan bus lines (gate electrodes) 22 are composed of 480 lines, the scan timing for each line is shown in FIG. 5B, and the scanning of all lines constitutes one frame. It At this time,
A document is set, and each photodiode of the liquid crystal panel 23 receives the transmitted light from the backlight corresponding to the image described on the document. Therefore, as described with reference to FIGS. 3A and 3B, when the photodiode 25 receives light, the photocurrent I _p flows for the period of one frame (may be several frames) and the potential of the corresponding pixel electrode 23 is changed. Reduce. When the photodiode 25 does not receive light, no photocurrent flows and the potential of the corresponding pixel electrode 23 is almost maintained.

Therefore, FIG. 6 shows a configuration diagram of reading the pixel potential at the time of reading the original. In FIG. 6, the analog switch 63 is controlled to the read terminal side when reading the pixel potential. Therefore, by sequentially scanning the scan bus line (gate electrode) 22 in the liquid crystal panel 42, the data potential of each pixel electrode 23 of each line is read out from each data bus line (drain potential) 21, and is latched by the latch 64. The data is latched and sent to the comparator 65 for each line.

The comparator 65 compares the data voltage for each pixel electrode 23 sent from the data bus line (drain electrode) 21 for each line from the latch 64 with the data voltage for writing, and the difference between them. When exceeds a predetermined value, it is discriminated that the photodiode 25 corresponding to the corresponding pixel electrode 23 has received light.

The identification signals of the light receiving state of these photodiodes 25 are supplied as image reading data to the personal computer through the interface 66, and when the scanning of all the scan bus lines (gate electrodes) 22 is completed. The image reading of the set original is completed.

As described above, when the data voltage is read from each pixel electrode 23, the photodiode 25 determines a sufficient pixel potential for one frame, so that the influence of external noise is avoided and the noise resistance is improved. Is achieved. By the way, during the normal display by the liquid crystal panel 42, the photodiode 25 by the light of the backlight 52 is used.
Although the pixel potential decreases due to the reception of light, since the light from the backlight is uniform, the decrease in each pixel potential is also uniform, and it is possible to easily correct it by giving a correction value to the data voltage all at once. Is something that can be done.

The backlight 52 is used during image reading.
By increasing the brightness of the photodiode 25
Since the photocurrent due to the reception of light and the decrease in the potential of the pixel electrode 23 increase, the noise resistance can be further improved. Next, FIG. 7 shows a circuit configuration diagram of a main part of another embodiment of the present invention. FIG. 7A shows a structure in which the anode side of the photodiode 25 shown in FIG. 1 is connected to the auxiliary electrode 26 instead of the gate electrode (n-1) 22 immediately before, and other structures are the same as those shown in FIG. It is the same. in this case,
The potential of the auxiliary electrode 26 is set lower than the potential of the pixel electrode 23, and a constant voltage is supplied to the photodiode 25.

That is, when the photodiode 25 receives light in a scanning period of a predetermined number of frames, the potential of the pixel electrode 23 is reversely biased by causing the photocurrent I _p to flow from the pixel electrode 23 in which the data voltage is written. The writing and reading of the data voltage are the same as in the case of FIG. 1 and have the same effect.

In FIG. 7B, the connection between the anode side and the cathode side of the photodiode 25 in FIG. 7A is reversed, and the potential of the auxiliary electrode 26 is set higher than that of the pixel electrode 23. The other structure is similar to that of FIG. That is, the anode of the photodiode 25 is connected to the pixel electrode 23, and the cathode is connected to the auxiliary electrode 26.

In this case, the pixel electrode 2 in which the data voltage is written by the photodiode 25 receiving light according to the original document.
A photocurrent is passed through 3 to increase the potential of the pixel electrode 23. Therefore, in the pixel electrode 23, the written data voltage is compared with the potential increased by the light reception of the photodiode 25 in the scanning period of the predetermined number of frames, and when the predetermined value is exceeded, the light reception state of the photodiode 25 is compared. Can be identified, and the operation principle is the same as that in FIGS. 1 and 7A, and has the same effect.

In the above embodiment, the transistor T _{r is used.}
Although it is shown as an n-type transistor, a P-type transistor made of polycrystalline silicon may be used. In this case, the pixel electrode 2
Writing to 3 is similar to the above, but since the potential of the scan side (gate electrode) 22 is inverted, the anode side of the photodiode 25 is connected to the pixel electrode 23 and the cathode side of the previous one is connected. It may be connected to the auxiliary electrode 26 having a potential higher than that of the gate electrode (n-1) 22 or the pixel electrode 23.

[0042]

As described above, the first, second, third, fourth and sixth aspects are provided.
According to the invention of claim 7, one end of the light detecting means is connected to the pixel electrode and the other end is connected to the constant voltage portion in a state of being reverse-biased with the pixel electrode during non-light detection,
The electric potential of the pixel electrode is changed in the light detection state of the light detection unit by causing the data supply unit to write in the pixel electrode when the control unit reads the image. For example, the pixel electrode is switched by the switching unit after a scanning period of a predetermined number of frames. By reading out the potential of the photodetector and discriminating the photodetection of the photodetector by the discriminator, the influence of external noise on the photodetection by the photodetector is avoided because the potential of the pixel electrode is read after a predetermined period. The noise resistance can be improved.

According to the invention of claim 5, by making the driving means have a bidirectional function, writing to the pixel electrode,
It is possible to perform a single read. According to the invention of claim 8, a light irradiating means for irradiating light at the time of liquid crystal display is provided, and by increasing the brightness by the light irradiating means at the time of writing the pixel electrode for image reading, noise resistance can be improved. It can be further improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is an internal configuration diagram of FIG.

FIG. 3 is an explanatory diagram of an operation principle of the photodiode of FIG.

FIG. 4 is a conceptual diagram of document reading according to the present invention.

FIG. 5 is a configuration diagram of writing to a pixel electrode when reading a document.

FIG. 6 is an explanatory diagram of reading pixel potentials when reading a document.

FIG. 7 is a circuit configuration diagram of a main part of another embodiment of the present invention.

FIG. 8 is a circuit diagram of a main part of a conventional active matrix liquid crystal display device.

[Explanation of symbols]

 21 Drain Electrode 22 Gate Electrode 23 Pixel Electrode 24 Counter Electrode 25 Photodiode 26 Correction Electrode 42 Liquid Crystal Panel 51 Active Matrix Liquid Crystal Display 52 Backlight 53 Original 61 Serial Parallel Converter 62, 64 Latch 63 Analog Switch 65 Comparator 66 Interface

Claims (8)

[Claims] 1. A predetermined number of scan bus lines and data bus lines are arranged in a grid pattern, and pixel electrodes and counter electrodes for sandwiching liquid crystal are arrayed in a matrix in a surrounded portion. In an active matrix type liquid crystal display device including a driving means for driving the pixel electrode by signals from the scan canvas line and the data bus line, one end is connected to the pixel electrode and the other end is connected to a constant voltage portion to detect light. And a control unit that causes the drive unit to write to the pixel electrode during image reading, and that identifies the light detection of the light detection unit by the potential of the pixel electrode after a predetermined scanning period. An active matrix liquid crystal display device characterized by: 2. The light detection means according to claim 1, wherein one end of the cathode side is connected to the pixel electrode, and the other end of the anode side is connected to a scan bus line one line before the corresponding scan bus line. An active matrix liquid crystal display device characterized by the above. 3. The light detection means according to claim 1, wherein one end of the cathode side is connected to the pixel electrode, and the other end of the anode side is connected to an auxiliary electrode having a potential lower than that of the pixel electrode. Active matrix liquid crystal display device. 4. The photo-detecting means according to claim 1, wherein one end of the anode side is connected to the pixel electrode, and the other end of the cathode side is connected to an auxiliary electrode having a higher potential than the pixel electrode. Active matrix liquid crystal display device. 5. The active matrix type liquid crystal display device according to claim 1, wherein the driving means has a bidirectional function of writing and reading with respect to the pixel electrode. 6. The control means according to claim 1, wherein the data supply means supplies a data voltage when writing to the pixel electrode, the determination means which reads and compares the potential of the pixel electrode at the time of reading, and the data supply means. An active matrix type liquid crystal display device, comprising: a switching unit for switching between a discriminating unit and a discriminating unit. 7. The active matrix liquid crystal display device according to claim 1 or 6, wherein the pixel electrode is read out after a scanning period of a predetermined number of frames from the writing. 8. The light irradiating means according to claim 1, further comprising a light irradiating means when displaying with the liquid crystal.
When writing to the pixel electrode during image reading,
An active matrix type liquid crystal display device, characterized in that the brightness is increased by the light irradiation means.