JPH09243995A - Active matrix array, liquid crystal display device and its drive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contribute to low power consumption in a liquid crystal display system using a TFT or a computer system such as a personal portable terminal (PDA), etc., using it. SOLUTION: A latch circuit 3 storing an image data signal and a drive signal generation circuit 4 driving a liquid crystal 8 based on the image data signal stored in the latch circuit 3 are provided answering to each of plural pixels arranged in matrix. Further, a set of a scanning line, a data signal line, the latch circuit, the drive signal generation circuit and a pixel electrode is made a sub-pixel, and each pixel is constituted of plural sub-pixels, and an area ratio of the pixel electrode of each sub-pixel is changed nearly twice each.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix array using thin film transistors (hereinafter abbreviated as TFT), a liquid crystal display device using the same, and a driving method thereof.

[0002]

2. Description of the Related Art A liquid crystal display device using a TFT is a flat panel display capable of displaying high quality images.
Nowadays, it is used in a wide range of fields such as laptop computers, car navigation systems, TV monitors, measuring instruments, and other information devices. FIG. 6 is a circuit diagram of a main part of a liquid crystal display device using a conventional TFT. Screen part 100
The pixels 101 are arranged in a matrix, and each pixel is connected to a scanning line (horizontal wiring) 102 and a data signal line (vertical wiring) 103 formed vertically and horizontally. A scan circuit 104 which is a peripheral driver circuit and a data signal circuit 105 are provided, and the scan line 102 is connected to the scan circuit 104 and the data signal line 103 is connected to the data signal circuit 105. Further, a common wiring 106 on the fixed potential side of the additional capacitor provided in each pixel 101 and a connection circuit 107 for the common wiring 106 are provided. However, there is also a configuration in which a common line for an additional capacitor and a connection circuit are not separately provided and the scanning line in the preceding stage is also used. Although the number of pixels varies depending on the application of the liquid crystal display device, it has been commercialized from a small number of tens of thousands of pixels to a large capacity of more than 3 million pixels.

FIG. 7 is a circuit diagram of one pixel 101.
Pixel transistor (n-channel TFT in this figure)
A gate of 110 is connected to the scanning line 102, and a drain or a source thereof is connected to the data signal line 103 or the pixel electrode 111. Between the pixel electrode 111 and the counter electrode 112, an alignment-treated TN liquid crystal or the like is formed. The liquid crystal layer 113 is sandwiched, and a liquid crystal display can be performed by combining it with a polarizing plate or the like. The capacitor 114 is an additional capacitor that earns the holding time of the image signal.

In the above structure, the portion excluding the counter electrode and the liquid crystal layer is formed on the glass substrate as an active matrix array. The scanning circuit 104 and the data signal circuit 1 are formed by using a polysilicon thin film transistor.
In some cases, 05 is formed on the same glass substrate (peripheral drive circuit built-in active matrix array).

FIG. 8 is a schematic diagram of drive waveforms of a liquid crystal display device using a conventional TFT. The drive waveform is shown focusing on one pixel in the screen. Reference numeral 120 is a scanning signal applied to the scanning line 102, 121 is a drive signal applied to the data signal line 103, and 122.
Is the potential of the counter electrode 112 (counter electrode potential). At the timing when the scanning signal 120 rises to a positive pulse, the pixel transistor 110 is turned on, a drive signal is written in the pixel electrode, and the pixel electrode potential 123 appears in the pixel electrode. At this time, the voltage Vsig is applied to the liquid crystal layer 113.

When the pixel transistor 110 is turned off at the end of the positive pulse period of the scanning signal 120, Vsi
g gradually decreases with time due to leakage current and dielectric relaxation of the liquid crystal layer. In the case of FIG. 8, a bright state in the period a,
The driving is performed so that the period b is a dark state and the period c is a bright state (brightness and darkness can be reversed by using a polarizing plate). During this period, the peripheral drive circuit (scanning circuit 104, data signal circuit 105
Etc.) are always working. T described above
For details of the liquid crystal display device using the FT, for example, “Flat Panel Display '91” (Nikkei BP,
80-96 pages (issued on November 26, 1990) and many other magazines and journals.

[0007]

A liquid crystal display device is a CR
One of the outstanding features is that the power consumption is much lower than that of the T monitor, which is a major reason why it is widely used in notebook computers and the like. However, particularly in applications where it is difficult to use a commercial power source, such as applications requiring portability, further reduction in power consumption is desired. For example, T
Since the liquid crystal display device using FT has high image quality, a personal portable terminal (PDA), a telephone function, a TV
For portable multimedia terminals that combine functions,
It is expected that a liquid crystal display device using a TFT will be mounted.

However, in a liquid crystal display device using a conventional TFT, even a reflective type that does not use a backlight is several hundred meters.
Since it requires electric power of W to several W, the usable time of the battery is short, and drastic reduction of power consumption of the liquid crystal display device is necessary for full-scale popularization (of course, other peripheral circuits have low power consumption). Power consumption is also important).

Therefore, the present invention provides an active matrix array and a liquid crystal display device which can contribute to lower power consumption of a liquid crystal display system using a TFT or a computer system such as a PDA using the same, and a driving method thereof. The purpose is to provide.

[0010]

In order to achieve the above object, an active matrix array according to the present invention and a liquid crystal display device using the same are provided with an image corresponding to each of a plurality of pixels arranged in a matrix. It is characterized in that a latch circuit for storing a data signal and a drive signal generation circuit for generating a drive signal for driving a liquid crystal based on the image data signal stored in the latch circuit are provided.

According to the driving method of the present invention for such a liquid crystal display device, an image data signal is stored in a latch circuit provided in each pixel, and a polarity is set at a predetermined cycle based on the stored image data. Is generated continuously by a drive signal generating circuit a plurality of times.

The features of the above-described active matrix array, liquid crystal display device, and driving method thereof according to the present invention will be described below in comparison with a conventional example. T
In order to reduce the power consumption in the liquid crystal display device using the FT, suppressing the power consumption of the peripheral drive circuit has a great effect. Therefore, let us consider a case where the drive circuit is operated intermittently in the conventional drive method. FIG. 9 shows FIG.
The driving waveforms when the peripheral driving circuit is operated for ⅛ time in the conventional driving method described using FIG. In the case of FIG. 9, after writing one screen of data, 7
The screen data is not processed and ignored. As in the case of FIG. 8, the bright state is displayed in the period a, the dark state is displayed in the period b, and the bright state is displayed in the period c. Also in this case, when the positive pulse is applied to the scanning signal 130, the driving signal 13
1 is written in the pixel electrode, the pixel electrode potential 132 is gradually attenuated thereafter, and the image signal is not updated for a long time until the next operation of the peripheral drive circuit, that is, until a positive pulse is applied to the scan line 130. The voltage applied to the liquid crystal will vary greatly.

In such a situation, the following side effects occur, and the display is actually very poor. (A) Vsig fluctuates, and since the polarity reversal period is long, significant flicker is observed on the screen. (B) The contrast decreases due to the attenuation of Vsig. (C) Accurate AC driving of the liquid crystal is impaired and the life is shortened.

Although it depends on the display capacity, when writing a drive signal to a pixel in the form of sequentially scanning the screen, in order to process a normal image signal, a transfer rate of the image signal source is equal to or higher than several MHz. High speed operation at 100 MHz is required for the peripheral drive circuit. As for the load at the time of writing, the wiring capacitance of the data signal line, which is about 10 to 100 times the pixel capacitance, is actually charged and discharged. Further, even if the display contents do not change in the conventional driving, it is necessary to constantly move the peripheral driving circuit to prevent flicker.

On the other hand, in the configuration of the present invention, the latch circuit and the drive signal generating circuit are provided for each pixel, and even when the peripheral drive circuit is stopped, based on the image data stored in each pixel, A drive signal whose polarity is inverted in a predetermined cycle is continuously generated by the drive signal generation circuit a plurality of times.
That is, the image data signal is stored in the latch circuit in the pixel,
After that, stop (or wait) the peripheral drive circuit,
The generation of the drive signal whose polarity is inverted is performed in parallel at each pixel level. This parallel processing is several kHz to 10
Processing speed equivalent to kHz (normal video display is 20 to 10 m
Since the screen is rewritten in a cycle of s, about 1% thereof is sufficient). Further, the rewriting load is almost equal to the pixel capacity, and the capacity load at the time of rewriting due to the polarity inversion of the drive signal for one screen is reduced to about 1/10 to 1/100 as compared with the conventional case.

For this reason, the power consumption during the suspension period of the peripheral drive circuit is greatly reduced. In general, the power consumption is proportional to the frequency and the capacity serving as a load, so the power consumption when the peripheral drive circuit is stopped is extremely small. Further, since the AC drive can be accurately performed at intervals at which flicker is difficult to be recognized, the side effects such as (a) to (c) described above do not occur.

Preferably, a set of the scanning line, the data signal line, the latch circuit, the drive signal generating circuit, and the pixel electrode constitutes one sub-pixel, each pixel is composed of a plurality of sub-pixels, and each sub-pixel is composed of a plurality of sub-pixels. Gradation display is also possible by changing the area ratio of the pixel electrodes by approximately twice.

As a concrete structure, it is preferable that the latch circuit and the drive signal generating circuit provided in each pixel are formed of a polysilicon thin film transistor circuit formed on a glass substrate. Further, it is preferable that the peripheral circuits are simultaneously formed of polysilicon thin film transistor circuits. Other preferable specific configurations will be described in detail later.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to Examples and the drawings. [Embodiment 1] FIG. 1 shows a circuit configuration of one pixel of a liquid crystal display device according to an embodiment of the present invention. Scan line (horizontal wiring) 1
A latch (memory) circuit 3 is connected to and the data signal line (vertical wiring) 2. The latch circuit 3 has a function of storing the image data signal applied to the data signal line 2 when the selection pulse is input to the scanning line 1. A drive signal generating circuit 4 is connected to the latch circuit 3, and the drive signal generating circuit 4 stores the data stored in the latch circuit and the first signal.
A liquid crystal drive signal is generated based on the control signal applied to the control signal line 5a and the control signal applied to the second control signal line 5b and applied to the pixel electrode 6. TN with orientation treatment
The liquid crystal layer 8 is driven by the potential difference between the counter electrode 7 and the pixel electrode 6. A liquid crystal display device having such a circuit configuration is manufactured by a low temperature process (substrate heating temperature 650) on a glass substrate.
A CMOS polysilicon thin film transistor formed at (° C. or less) is used to form an active matrix array in which each circuit element is formed together with a peripheral drive circuit, a counter substrate, and liquid crystal.

As shown in FIG. 1, the latch circuit 3 is composed of an n-channel thin film transistor (A) and a capacitor C1, and one electrode of the capacitor C1 is connected to a common wiring 9. The drive signal generating circuit 4 is composed of an n-channel thin film transistor (B) and a p-channel thin film transistor (C), and the gate electrodes of the thin film transistors (B) and (C) are connected to the drain electrode of the thin film transistor (A) of the latch circuit 3. ing. The drain electrodes of the thin film transistors (B) and (C) are connected to the pixel electrode 6, the source electrode of the thin film transistor (B) is connected to the first control signal line 5a, and the source electrode of the thin film transistor (C) is second control. An active matrix array is formed by being connected to the signal line 5b. The capacitor C1 which is the additional capacitance may be replaced with the gate electrode capacitance of the thin film transistors (B) and (C). A liquid crystal display device is constructed by arranging the pixels having such a circuit configuration in a matrix like the configuration of the conventional example shown in FIG.

FIG. 2 shows drive waveforms (focusing on one pixel) of the liquid crystal display device configured as described above. Similar to FIG. 8 of the conventional example, the waveforms in the case of driving so as to be in a bright state in the period a, a dark state in the period b, and a bright state in the period c are schematically shown. In FIG. 2, scan signal 1
The signal 16 of the data signal line when the selection pulse (positive pulse) appears at 0 is stored in the latch circuit 3. 11 is a stored signal. In this embodiment, the H level digital signal is held in the dark state of the period b, and the L level digital signal is held in the bright state of the periods a and c.

The drive signal generating circuit 4 is provided with the latch circuit 3
A drive signal for applying a voltage to the liquid crystal layer is generated based on the image data signal 11 stored in. This drive voltage was set every 1/60 seconds according to the NTSC system.
Output is made so that the polarity is inverted at each mark timing. In this embodiment, the polarity of the counter electrode potential 13 is also inverted at each of the above timings. Then, a signal 17 in phase with the counter electrode potential 13 is applied to the first control signal line 5a, and a signal 18 in phase with the counter electrode potential is applied to the second control signal line 5b.

Image data 11 stored in the latch circuit 3
Is high, the n-channel thin film transistor (B) is turned on and the p-channel thin film transistor (C) is turned off in the circuit of FIG. 1, and the signal 17 is written in the pixel electrode 6. Note that the H level of the image data 11 is changed by the discharge of the capacitor C1 forming the latch circuit 3.
Although it gradually decreases as shown in FIG. 2, the capacitor C1 does not fall below the voltage level required to keep the transistor (B) on and the transistor (C) off for a predetermined period as described above. The capacity etc. are set.

On the contrary, when the image data 11 stored in the latch circuit 3 is at L level, the n-channel thin film transistor (B) is turned off, the p-channel thin film transistor (C) is turned on, and the signal 18 is applied to the pixel electrode 6. Will be written. Therefore, the pixel electrode potential is as shown in FIG.
The waveform becomes as indicated by 12.

A circuit corresponding to the conventional peripheral driving circuit (such as the scanning circuit 104 and the data signal circuit 105 in FIG. 6) operating at a high speed in the MHz class writes one screen as in the case of FIG. It operates only for a period. In FIG. 2, the peripheral drive circuit is operated only during the operation period 14 which is 1/8 of the entire period, and the operation is stopped during the other period 15.

When the polarity inversion is performed at the timing ↑ in the stop period (that is, the standby period) 15 of the peripheral drive circuit, the rewriting of the drive signal is collectively processed in parallel for all the pixels in the screen. In this way, the voltage Vsig applied to the liquid crystal is accurately AC-driven even during the period in which the peripheral drive circuit is stopped. Although not shown in the drawing, a liquid crystal display system was constructed by adding a stop mechanism of peripheral circuits and a control signal system for driving the liquid crystal display device.

By constructing the active matrix array and the liquid crystal display device as described above and stopping the peripheral drive circuit during the period of 7/8 in the driving method, the power consumption could be greatly reduced. In addition, there were no problems such as an increase in flicker, a decrease in contrast, and a shortened life due to the stop of the peripheral drive circuit. Of course, it is not necessary to limit the stop period of the peripheral drive circuit to 7/8, and it can be lengthened or shortened depending on the application. If a circuit corresponding to the stop period is manufactured at the same time as the peripheral drive circuit by using the polysilicon thin film transistor circuit on the glass substrate, the system becomes very efficient.

[Embodiment 2] A circuit diagram of one pixel in another embodiment of the present invention is shown in FIG. A set of the scanning line, the data signal line, the latch circuit, the drive signal generation circuit, and the pixel electrode is set as one sub-pixel, and two sets of sub-pixels are installed for each pixel, and the area ratio of the pixel electrode of each sub-pixel is set. It is changing twice. That is, sub-pixel (1) and sub-pixel (2)
The same structure as that of the first embodiment is installed in the first embodiment, but the area ratio between the sub pixel electrode 22 of the sub pixel (1) and the sub pixel electrode 23 of the sub pixel (2) is set to 1: 2. Has been done. This is shown in FIG. In the case of this configuration, the data applied to the data signal wiring 20 of the sub-pixel (1) and the data signal wiring 21 of the sub-pixel (2) are combined at the H level and the L level, and the same driving as in the first embodiment described above is performed. By doing so, four levels of display strength can be expressed.

FIG. 5 is a partial sectional view of a reflection type liquid crystal display device manufactured with the circuit configuration shown in FIG. 3
0 is a glass substrate, 31 is a TFT undercoat film, 3
Reference numeral 2 is an n-channel thin film transistor (B), and 33 is a p-channel thin film transistor (C). Reference numeral 34 is a wiring group, 35 is an interlayer insulating film, 36 is a reflective electrode having a finely roughened surface, 37 is a counter electrode, 39 is a liquid crystal layer, and two glass substrates are aligned by using an alignment film 38. Is trapped in between.

According to the active matrix array of this embodiment and the liquid crystal display device using the same, the power consumption can be reduced in the state where gradation display is possible. In this embodiment, two sub pixels are formed in one pixel, but the number of sub pixels may be increased. For example, one pixel is divided into six, and the area of each sub-pixel electrode is changed approximately twice (that is, the area ratio is set to 1: 2: 4: 8: 16: 32), whereby display of 64 gradations is possible. Becomes

[0031]

As described above, according to the present invention,
In a liquid crystal display device using a TFT, power consumption can be reduced extremely effectively. Further, gradation display is also possible. As a result, it is possible to contribute to the realization of a high-performance product such as a mobile terminal that can operate for a long time with one charge.

[Brief description of drawings]

FIG. 1 is a circuit diagram of one pixel of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a drive waveform focusing on one pixel of the liquid crystal display device of FIG.

FIG. 3 is a circuit diagram of one pixel of a liquid crystal display device according to another embodiment of the present invention.

FIG. 4 is a diagram showing an area ratio of a plurality of sub-pixels constituting one pixel of the liquid crystal display device of FIG.

5 is a cross-sectional view of a reflective liquid crystal display device configured using the pixels of FIG.

FIG. 6 is a circuit diagram of a main part of a conventional liquid crystal display device using a TFT.

FIG. 7 is a circuit diagram of one pixel of a conventional liquid crystal display device.

FIG. 8 is a schematic diagram of a drive waveform focusing on one pixel of a conventional liquid crystal display device.

FIG. 9 is a schematic diagram of drive waveforms when a peripheral drive circuit is intermittently operated in a conventional liquid crystal display device.

[Explanation of symbols]

 1 scan line 2 data signal line 3 latch circuit 4 drive circuit generating circuit 5a first control signal line 5b second control signal line 6 pixel electrode 7 counter electrode 8 liquid crystal layer 9 common electrode 10 scan signal 11 stored in a latch circuit Image data signal 12 image electrode potential 13 counter electrode potential 14 operation period of peripheral drive circuit 15 stop period of peripheral drive circuit 16 signal of data signal line 17 signal applied to first control signal line 18 second control signal line Signals applied to the electrodes 20,21 Data signal lines 22,23 Sub-pixel electrode 30 Glass substrate 31 Undercoat film 32 n-channel thin film transistor (B) 33 p-channel thin film transistor (C) 34 Wiring group 35 Inter-layer insulating film 36 Reflective electrode 37 Counter electrode 38 Alignment Film 39 Liquid Crystal Layer

Claims (10)

[Claims] 1. A latch circuit for storing an image data signal corresponding to each of a plurality of pixels arranged in a matrix, and a drive signal for driving a liquid crystal based on the image data signal stored in the latch circuit. And a drive signal generating circuit for generating the active matrix array. 2. A set of a scanning line, a data signal line, the latch circuit, the drive signal generating circuit, and a pixel electrode is defined as one sub-pixel, and each pixel is composed of a plurality of sub-pixels. The active matrix array according to claim 1, wherein the area ratio of the electrodes is changed by about twice. 3. The latch circuit comprises a thin film transistor (A) and a capacitance component, a gate electrode of the thin film transistor (A) is connected to a scanning line which is a horizontal wiring, and a source of the thin film transistor (A). 3. The active matrix array according to claim 1, wherein the electrodes are connected to data signal lines which are vertical wirings, and the drain electrodes of the thin film transistors (A) are connected to the electrostatic capacitance component and the drive signal generation circuit. 4. The drive signal generating circuit is composed of an n-channel thin film transistor (B) and a p-channel thin film transistor (C), and gate electrodes of these thin film transistors (B) and (C) are thin film transistors (L) of the latch circuit. A), the drain electrodes of the thin film transistors (B) and (C) are connected to pixel electrodes, and the source electrodes of the thin film transistors (B) are connected to a first control signal line. 4. The active matrix array according to claim 3, wherein the source electrode of C) is connected to the second control signal line. 5. The active matrix array according to claim 1, wherein the latch circuit and the drive signal generation circuit provided in each pixel are formed by a polysilicon thin film transistor circuit formed on a glass substrate. 6. A liquid crystal display device using the active matrix array according to claim 1. 7. The liquid crystal display device according to claim 6, wherein the pixel electrode is a reflective electrode. 8. A method for driving a liquid crystal display device according to claim 6, wherein an image data signal is stored in a latch circuit provided in each pixel, and a predetermined cycle is set based on the stored image data. A method for driving a liquid crystal display device, wherein a drive signal whose polarity is inverted is continuously generated a plurality of times by a drive signal generation circuit. 9. A method for driving a liquid crystal display device using the active matrix array according to claim 4.
An H-level or L-level image data signal is applied to the data signal line, a bright display signal is applied to one of the first and second control signal lines, and a dark display signal is applied to the other, and the thin film transistor (A) The image data signal is stored in the latch circuit by applying a selection pulse to a scanning line connected to the gate electrode of the n-channel thin film transistor (B) and the p-channel thin film transistor according to the stored image data signal. One of (C) is in the ON state and the other is in the OFF state, and the signal of either one of the first and second control signal lines is supplied until the next selection pulse is applied to the scanning line. 9. The method for driving a liquid crystal display device according to claim 8, wherein is written in the pixel electrode. 10. The active matrix array according to claim 1, wherein the peripheral circuit is formed of a polysilicon thin film transistor at the same time as the pixel portion in order to apply the driving method of the liquid crystal display device according to claim 9.