JP2002140052A - Portable information device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the power consumption of a portable information device. SOLUTION: In pixels, a plurality of storage circuits and liquid crystal cells are arranged and digital video signals are stored for every pixel. For a still picture, information written to the pixels after information is written to the pixels once is the same, so the still picture can continuously be displayed by reading the signals out of the storage circuits without inputting signals by frames. Namely, when the still picture is displayed, processing operation for signals of at least one frame is performed and then a source signal line driving circuit can be stopped thereafter, so that the power consumption can greatly be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a portable information device and a driving method thereof, and more particularly, to a portable telephone, a PDA (Personal D) having a flat display using liquid crystal or the like.
igital Assistant), portable personal computers, portable game devices,
The present invention relates to a portable information device such as a portable navigation system and an electronic book.

[0002]

2. Description of the Related Art In recent years, mobile phones have become widespread due to the development of communication technology. In the future, the transmission of moving images and the transmission of more information are expected. On the other hand, personal computers have been manufactured for mobile devices due to their light weight. A large number of information devices called personal digital assistants, which started with electronic notebooks, have been produced and are becoming popular. In addition, due to the development of liquid crystal display devices and the like, most of these portable devices are equipped with flat displays.

[0003] As a more recent technology, active matrix display devices have begun to be used in these portable devices. The active matrix type display device has a pixel 1
One TFT is arranged for each TFT, and the TFT
Is controlled by the screen. Such an active-matrix display device has advantages over a passive-matrix display device in that it can support higher definition of an image, can improve image quality, and can support moving images. Therefore, it is expected that display devices of portable information devices will change from passive matrix type to active matrix type in the future.

[0004] Among active matrix display devices, display devices using low-temperature polysilicon have recently been commercialized. With the low-temperature polysilicon technology, a driving circuit can be simultaneously formed using a TFT in a peripheral portion of a pixel portion in addition to a pixel TFT forming a pixel. Therefore, a liquid crystal display device (a display device having a liquid crystal cell) is indispensable for a display unit of a mobile device, which greatly contributes to miniaturization and low power consumption of the device, and accordingly, its application field is remarkably expanding in recent years. It is becoming a device.

FIG. 11 shows a block diagram of a conventional portable information terminal. Reference numeral 1204 denotes a power supply. In a portable information terminal, it is required that a user derives information required as needed. The information refers to the storage device (D
RAM 1209, flash memory 1210, etc.), those stored in a memory card 1203 inserted into a portable information terminal, and those obtained by connecting to an external device via an external interface port 1205.

A user's instruction input from a pen input tablet 1201 is read as electronic information by a detection circuit 1202. The electronic information is transmitted to the video signal processing circuit 120 by the tablet interface 1218.
7 The video signal processing circuit 1207 converts the read electronic information into image data based on the image format stored in the VRAM 1211 and sends the image data to the controller 1212. Here, the controller 1212
Generates a signal for driving the display device 1213, drives the display device 1213, and performs display.

FIG. 12 shows a block diagram of a conventional portable telephone. The same reference numerals are given to the portable information terminals shown in FIG. 11 which are already shown.

A portable telephone is a transmitting / receiving circuit 1 for transmitting / receiving radio waves.
224 and an audio processing circuit 1 for performing audio processing on the received signal
221, a speaker 1223, a microphone 1222, a keyboard 1220 for inputting data, a display device 1213 for display, an LCD controller 1212 thereof, and storage devices (VRAM 1211, DRAM 1209, flash memory 1210, etc.).

In the portable telephone shown in FIG. 12, a keyboard interface 1238 and a video signal processing circuit 1
The operations of 207, VRAM 1211 and LCD controller 1212 are the same as those of the portable information terminal shown in FIG. The only difference is that the user's instructions are read as electronic information on the keyboard 1220.

FIG. 13 shows a detailed configuration of the transmission / reception circuit 1224 in FIG. Electronic information including audio information is received at an antenna 1302. Then, only necessary data is extracted from the electronic information in the filter 1303, and the amplifier 130
5 is input. The data input to the amplifier 1305 is amplified and input to the filter 1307. Filter 1
The data from which unnecessary information has been cut in 303 is
The frequency is raised in the first frequency conversion circuit 1309 and input to the filter 1312.

The data from which unnecessary information has been cut in the filter 1312 has its frequency raised again in the second frequency conversion circuit 1313 and is input to the filter 1316.

The data from which unnecessary information has been cut by the filter 1316 is amplified by the amplifier 1317 and input to the data demodulation circuit 1318.

The data demodulation circuit 1318 decodes the encoded data and inputs the decoded data to the CPU 1206.

Conversely, data sent from the CPU is input to the data modulation circuit 1319 and encoded. The phase of the encoded data is adjusted by the orthogonal transformer 1315 and its frequency is raised, and the frequency
311 is inputted.

The data input to the frequency conversion circuit 1311 is input to the filter 1308 with its frequency raised. The data from which unnecessary information has been cut by the filter 1308 is amplified by the amplifier 1306,
The signal is input to the filter 1303 via the switch 1304.

The data from which unnecessary information has been cut by the filter 1303 is transmitted by the antenna 1302.

FIG. 14 is a schematic diagram of a display device having a liquid crystal cell driven by a conventional digital method. The display device includes a pixel portion 9003 and a source signal line driver circuit 9001.
And a gate signal line driving circuit 9002.

The pixel portion 9003 has a plurality of pixels 9004. The source signal line driver circuit 9001 includes a shift register circuit 9001-1, a latch circuit A9001-
2. Latch circuit B9001-3, D / A conversion circuit 900
1-4. Also, the gate signal line driving circuit 900
2 includes a shift register circuit 9002-1 and a buffer circuit 9002-1.

FIG. 15 is a circuit diagram of the pixel 9004. The pixel 9004 has one of the source signal lines 9005 and one of the gate signal lines 9006. Pixel 900
Reference numeral 4 denotes a pixel TFT 9007, a liquid crystal cell 9008 having a liquid crystal interposed between a counter electrode and a pixel electrode, and a capacitor 9009.
Are provided.

A gate electrode of the pixel TFT 9004 is connected to a gate signal line 9006. Also, pixel TFT
One of a source region and a drain region 9004 is connected to a source signal line 9005, and the other is connected to a pixel electrode and a capacitor 9009 included in a liquid crystal cell 9008.

The capacitor 9009 is a pixel TFT 9007
Is provided to hold the potential of the pixel electrode when is in a non-selected state (off state).

A counter potential is applied to a counter electrode of the liquid crystal cell 9008.

A clock signal (C) is supplied to the shift register circuit 9001-1 of the source signal line driving circuit 9001.
K), a start pulse (SP) is input. The shift register circuit 9001-1 outputs these clock signals (C
K) and sequentially generates a timing signal based on the start pulse (SP), and sequentially supplies the timing signal to the latch circuit A9001-2.

The latch circuit A9001-2 has a plurality of latches for storing digital video signals. When the timing signal is input, the latch circuit A9001-2 sequentially captures the digital video signal into each latch,
Hold.

The time required to complete the writing of the digital video signal to all the latches of the latch circuit A9001-2 is called a line period. Actually, a period in which the horizontal retrace period is added to the line period may be referred to as a line period.

After the end of one line period, the latch circuit B90
A latch signal (LatchSignal) is supplied to 01-3. At this moment, the digital video signal written and held in the latch circuit A9001-2 is transferred to the latch circuit B9.
001-3 and sent to the latch circuit B9001-
3 are written and held.

The digital video signal is latched by a latch circuit B900.
Based on the timing signal from the shift register circuit 9001-1, the digital video signal is sequentially written again into the latch circuit A9001-2 which has finished sending to 1-3.

During the second one line period, the digital video signals written and held in the latch circuit B9001-3 are sequentially input to the D / A conversion circuit 9001-4.

The digital video signal is converted into an analog video signal (analog video signal) in the D / A conversion circuit 9001-4 and supplied to the source signal line 9005.

On the other hand, a clock signal (CL) is supplied to the shift register circuit 9002-1 in the gate signal line driving circuit 9002.
K), when the start pulse signal (SP) is input, a selection signal for controlling the switching of the pixel TFT 9007 is generated. The selection signal is buffer-amplified in the buffer circuit 9002-2 and input to the gate signal line 9006.

The pixel TFT 9004 is turned on by the selection signal input to the gate signal line 9006,
The analog video signal input to the source signal line is a pixel T
The signal is input to a pixel electrode included in the liquid crystal cell 9008 through the FT.

The liquid crystal is driven by the potential of the analog video signal input to the pixel electrode, the amount of transmitted light is controlled, and a part of an image (an image corresponding to the pixel) is displayed on the pixel.

When a part of the image is displayed in all the pixels, one image is displayed in the pixel portion 9003.

By performing the above operation in each pixel, one image is displayed.

[0035]

[Problems to be solved by the invention]

In the conventional information terminal device as described above, when a display screen is displayed, even if the screen is a still screen, the same video data is transmitted to the display device 60 times per second. I kept sending. That is, the CPU 120
6, video signal processing circuit 1207, VRAM 121
1, the source signal line driver circuit and the gate signal line driver circuit included in the controller 1212 and the display device 1213 operate as long as display is performed.

In a passive display device having a small number of pixels, a memory is provided by a driver IC or LC of the display device.
Although there is a device built in the D controller and stopping the VRAM, in a display device using a large number of pixels such as an active matrix, having a memory in a driver or in a controller is, from the viewpoint of a chip size,
Unrealistic. Therefore, in a conventional information terminal device, many circuits must continue to operate even when a still image is displayed, which hinders reduction in power consumption.

In portable information terminals, low power consumption is greatly desired. Furthermore, in this mobile device, even though it is mostly used in the still image mode, the driving circuit continues to operate even when the still image is displayed as described above. This is a drag on power consumption.

The present invention has been made in consideration of the above-described problems, and has as its object to reduce the power consumption of a driving circuit when a still image is displayed by using a novel circuit.

[0040]

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention uses the following means.

A plurality of storage circuits are arranged in a pixel, and a digital video signal is stored for each pixel. In the case of a still image, once the writing is performed, the information written to the pixels thereafter is the same. Therefore, the signal stored in the storage circuit can be read out by reading the signal stored in the storage circuit without inputting the signal for each frame. Can be displayed continuously. That is, when a still image is displayed, the source signal line driving circuit can be stopped after the signal processing operation for at least one frame has been performed, and accordingly, power consumption can be greatly reduced. Becomes possible.

Hereinafter, the configuration of the liquid crystal display device of the present invention will be described.

According to the present invention, in a portable information device having a display device and a controller, the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and when the display device displays a still image, A portable information device is provided in which a video display function other than the display device and the controller is stopped.

According to the present invention, in a portable information device having a display device and a controller, the display device includes a plurality of pixels each including a storage circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode of the liquid crystal cell. And a portable information device characterized in that when the display device displays a still image, a video display function other than the display device and the controller is stopped.

The controller may be a clock generation circuit of a display device.

According to the present invention, in a portable information device having a display device, the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and when the display device displays a still image, video information is displayed. A portable information device is provided, wherein a signal of the portable information device is not input to the display device from outside the display device.

According to the present invention, in a portable information device having a display device, the display device has a plurality of pixels each including a storage circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode of the liquid crystal cell. A portable information device is provided, wherein when the display device displays a still image, a signal having video information is not input to the display device from outside the display device.

According to the present invention, in a portable information device having a display device and a CPU, the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and when the display device displays a still image, A portable information device is provided, wherein the image display function of the CPU is stopped.

According to the present invention, in a portable information device having a display device and a CPU, the display device includes a plurality of pixels each including a storage circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode of the liquid crystal cell. Has,
A portable information device is provided, wherein when the display device displays a still image, the video display function of the CPU is stopped.

According to the present invention, in a portable information device having a display device and a VRAM, the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and the display device displays a still image. And a portable information device which stops calling data stored in the VRAM.

According to the present invention, in a portable information device including a display device and a VRAM, the display device includes a plurality of storage circuits, a liquid crystal cell, and a plurality of TFTs each of which controls a voltage applied to a pixel electrode of the liquid crystal cell. Pixel, and when the display device displays a still image, the VRA
A portable information device is provided, wherein the calling of data stored in M is stopped.

According to the present invention, in a portable information device having a display device, the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and when the display device displays a still image, the display device performs the display. A portable information device is provided, wherein the source signal line driving circuit of the device is stopped.

According to the present invention, in a portable information device having a display device, the display device has a plurality of pixels each including a storage circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode of the liquid crystal cell. In addition, a portable information device is provided in which the source signal line driving circuit of the display device is stopped when the display device displays a still image.

The storage circuit may be called once during one frame period.

According to the present invention, in a portable information device having a display device, the display device has a plurality of pixels, the plurality of pixels has a storage circuit and a liquid crystal cell, and among the plurality of pixels, A portable information device including means for rewriting data stored in a storage circuit included in a pixel in a specific row or column is provided.

According to the present invention, in a portable information device having a display device, the display device has a plurality of pixels, and the plurality of pixels apply a voltage applied to a storage circuit, a liquid crystal cell, and a pixel electrode included in the liquid crystal cell. A portable information device, comprising: a control TFT; and means for rewriting data stored in a storage circuit included in a pixel in a specific row or column among the plurality of pixels.

The portable information device may be a portable telephone, a personal computer, a navigation system, a PDA or an electronic book.

[0058]

FIG. 1 shows the configuration of the present invention. In the present invention, when a still image is displayed, display is performed by storing a video signal in a storage circuit inside a pixel of the display device 2213 and calling the stored video signal. Accordingly, the video signal processing circuit 2107 and the VRAM 21
11. Still images can be displayed without driving the source signal line driver circuit in the display device 2213. Note that information required by the user can be extracted from the external device via the external interface port 2105 as needed. In addition, information stored in the memory card 2103 inserted into the portable information terminal can be extracted. Reference numeral 2104 denotes a power supply.

The contents will be specifically described below.

If the input from the pen input tablet 2101 is not performed for a certain period of time, or if there is no signal input for changing the video display from the external input terminal for a certain period of time, the CPU 2106 determines that the mode is the still image mode. I do.

When the CPU 2106 makes such a determination, the CPU 2106 performs the following operation. The source signal line driver circuit of the display device 2213 is stopped via the LCD controller 2112. Specifically, the operation of the source signal line driver circuit can be stopped by stopping the supply of the start pulse, the clock signal, and the video data signal to the source signal line driver circuit. At this time, the gate signal line driver circuit does not stop but receives a signal and performs an operation of supplying data of a memory circuit provided in a pixel portion in the display device 2213 to a pixel electrode of each pixel.

Since the gate signal line driving circuit is generally driven at a frequency of 1/100 or less as compared with the source signal line driving circuit, there is no problem in terms of power consumption even if the operation is not stopped. . Of course, in the case of using a liquid crystal material which does not cause a problem in image quality of the liquid crystal display device, for example, a burn-in phenomenon, the gate signal line driving circuit may be stopped. With such an operation, the display device performs display by stopping only the gate signal line driver circuit or both signal line driver circuits.

Next, the CPU 2106 stops the signal processing circuit inside the CPU 2106 and the VRAM 2111. As described above, since the display device 2213 performs display using the video data stored in the internal storage circuit, when displaying a still image, the display device 2213 newly displays the video data.
There is no need to send to Therefore, video data is generated,
The video signal processing circuit 2107 to be processed, the tablet interface 2118, the VRAM 2111, and the like need not be operating. Further, it is not necessary to access a storage circuit such as the DRAM 2109 and the flash memory 2110 which holds information required by the user.

As described above, power reduction in the CPU 2106, power reduction in the VRAM 2111, and power reduction in the source signal line driving circuit are achieved.

When a signal is input again from an external input terminal of the pen input tablet 2101 or the like, the detection circuit 2102 of the pen input tablet 2101 transmits the signal to the CPU 21.
06 is instructed to change the display contents. Then, the CPU 2106 stops the VRAM 2111,
The tablet interface 2118 and the video signal processing circuit 2107 are operated. Then, a start pulse, a clock signal, and video data are supplied to the source signal line driver circuit of the display device 2213 through the LCD controller 2112, and a new video signal can be written to a pixel.

FIG. 2 shows an example of a portable telephone using the present invention. The operation outline is almost the same as that of the portable information terminal of FIG. Unlike mobile information terminals, mobile phones use keyboards to input data,
It is input to the antenna via the communication system of the telephone company,
After being amplified by the transmission / reception circuit shown in FIG. 3, it is controlled by the CPU and sent to the display device. When displaying a still image, the video signal processing circuit,
The VRAM, the source signal line driver circuit, and the like can be stopped.

[0067]

Embodiments of the present invention will be described below.

(Embodiment 1) In this embodiment, the configuration of a portable telephone having the configuration of the present invention will be described.

FIG. 2 is a block diagram of the portable telephone according to the present embodiment. The same reference numerals are given to the portable information terminals shown in FIG. 1 which are already shown.

The portable telephone is a transmitting and receiving circuit 2 for transmitting and receiving radio waves.
And an audio processing circuit 2 for performing audio processing on the received signal
121, a speaker 2123, a microphone 2122, a keyboard 2120 for inputting data, a display device 2113 for display, an LCD controller 2112, and storage devices (VRAM 2111, DRAM 2109, flash memory 2110, etc.).

In the portable telephone shown in FIG. 2, the keyboard interface 2138 and the video signal processing circuit 21
07, VRAM2111, LCD controller 2
The operation of 112 is the same as that of the portable information terminal shown in FIG. The only difference is that the user's instructions are read as electronic information on the keyboard 2120. External data is input to an antenna via a communication system of a telephone company, and transmitted and received by a transmission / reception circuit 22 shown in FIG.
After being amplified at 24, it is controlled by the CPU 2106 and sent to the display device 2213.

If the input from the keyboard 2220 is not performed for a certain period of time, or if there is no signal input for changing the video display from the external input terminal for a certain period of time, the CPU 2106 determines that the mode is the still image mode. .

When the CPU 2106 makes such a determination, the CPU 2106 performs the following operation. The source signal line driver circuit of the display device 2213 is stopped via the LCD controller 2112. Specifically, the operation of the source signal line driver circuit can be stopped by stopping the supply of the start pulse, the clock signal, and the video data signal to the source signal line driver circuit. At this time, the gate signal line driver circuit does not stop, receives a signal, and supplies data of a storage circuit provided in a pixel portion in the display device 2213 to a pixel electrode of each pixel.

Since the gate signal line driving circuit is generally driven at a frequency of 1/100 or less as compared with the source signal line driving circuit, there is no problem in terms of power consumption even if the operation is not stopped. . Of course, in the case of using a liquid crystal material which does not cause a problem in image quality of the liquid crystal display device, for example, a burn-in phenomenon, the gate signal line driving circuit may be stopped. With such an operation, the display device performs display by stopping only the gate signal line driver circuit or both signal line driver circuits.

Next, the CPU 2106 stops the signal processing circuit inside the CPU 2106 and the VRAM 2111. As described above, since the display device 2213 performs display using the video data stored in the internal storage circuit, when displaying a still image, the display device 2213 newly displays the video data.
There is no need to send to Therefore, video data is generated,
The video signal processing circuit 2107 to be processed, the keyboard interface 2138, the VRAM 2111, and the like need not be operating. Further, it is not necessary to access a storage circuit such as the DRAM 2109 and the flash memory 2110 which holds information required by the user.

As described above, power reduction in the CPU 2106, power reduction in the VRAM 2111, and power reduction in the source signal line driving circuit are achieved.

When a signal is input again from an external input terminal such as the keyboard 2220, the keyboard 2220
20 instructs the CPU 2106 to change the display content. Then CPU2106 stopped V
RAM 2111, keyboard interface 2138,
The video signal processing circuit 2107 is operated. And LC
A start pulse, a clock signal, and video data can be supplied to the source signal line driver circuit of the display device 2213 through the D controller 2112, and a new video signal can be written to a pixel.

(Embodiment 2)

In this embodiment, a detailed structure of a pixel portion included in a display device used in the present invention will be described.

In the pixel portion, a plurality of pixels 70 are arranged in a matrix.
4 are arranged. An enlarged view of the pixel 704 is shown in FIG. The pixel 704 includes a pixel TFT 705 and an SRAM 707
And a liquid crystal cell 7 having a liquid crystal interposed between the counter electrode and the pixel electrode.
08 is provided.

The gate electrode of the pixel TFT 705 is connected to a gate signal line 709. The pixel TFT 70
One of the source region and the drain region 5 is connected to the source signal line 710, and the other is connected to the input side of the SRAM 707.

The SRAM 707 has a p-channel type TFT and an n-type TFT.
It has two channel type TFTs, and the source region of the p-channel type TFT is connected to the high voltage side power supply line 711 and is kept at the voltage Vddh. Also, n-channel type T
The source region of the FT is connected to the low voltage side power supply line 712 and is kept at the voltage Vss. Vddh> Vs
s. One p-channel TFT and one n-channel TFT are paired, and one SRAM has two pairs of p-channel TFTs and n-channel TFTs.

The drain regions of the paired p-channel TFT and n-channel TFT are connected to each other. The gate electrodes of the paired p-channel TFT and n-channel TFT are connected to each other. And a pair of p-channel and n-channel T
The drain region of the FT is kept at the same potential as the gate electrode of the other pair of p-channel and n-channel TFTs. The drain region of one pair of p-channel and n-channel TFTs is an input side to receive an input signal (Vin), and the drain region of the other pair of p-channel and n-channel TFTs is an output signal. (Vout)
Is the output side where is output.

The SRAM is designed to hold Vin and output Vout which is a signal obtained by inverting Vin. That is, if Vin is Hi, Vout becomes a Lo signal equivalent to Vss, and if Vin is Lo, Vout becomes Vd.
It becomes a Hi signal equivalent to dh.

The output side of the SRAM 707 is connected to the liquid crystal cell 70.
8 is connected to the pixel electrode.

The pixel TFT 705 is turned on by the selection signal input to the gate signal line 709. The digital video signal input to the source signal line 710 is input as Vin to the input side of the SRAM 707 via the pixel TFT 705.

The input digital video signal is held until the next digital video signal is input. Also S
A RAM requires less time to write a digital video signal than a DRAM and can write data at high speed.

The digital video signal has information of 1 or 0, and the digital video signal input to the SRAM 707 is output with its information inverted. For example, 1
Is input to the SRAM 707, a digital video signal having information of 0 is output from the output side of the SRAM 707 as Vout. Conversely, a digital video signal having information of 0 is SRA
When input to M707, a digital video signal having 1 information is output as Vout from the output side of SRAM 707.

The digital video signal output from the output side of the SRAM 707 is input to the pixel electrode of the liquid crystal cell 708. Then, the liquid crystal is driven according to the information of 1 or 0 included in the digital video signal, and the transmitted light amount is controlled.

Similarly, by inputting a digital video signal to all pixels, it is selected whether or not the liquid crystal cell of each pixel emits light.

When all the bits of the digital video signal are input to all the pixels, one image is displayed. During one frame period, gradation display may be performed by controlling the length of the period in which the liquid crystal cell of each pixel transmits light, or a plurality of pixels may be used as one unit to transmit light. Gray scale display may be performed by controlling the area of a pixel having a liquid crystal cell.

By providing an SRAM in a pixel in the present invention, a digital video signal input to a pixel can be held more reliably until the next digital video signal is input. That is, it is possible to prevent the charge held in the pixel electrode of the liquid crystal cell 708 from decreasing due to the leak current of the pixel TFT, and to prevent the transmitted light amount of the liquid crystal cell from changing.

Note that a volatile memory can be formed using a TFT, and thus can be formed simultaneously with a pixel TFT.

In the present invention, it is not necessary to positively provide a storage capacitor. When the storage capacitor is not provided, the time for inputting the digital video signal to the pixel can be shortened. Therefore, even if the number of pixels of the liquid crystal display increases,
The length of the writing period can be reduced.

This embodiment can be implemented by freely combining with the configuration shown in the first embodiment.

(Embodiment 3)

In this embodiment, a detailed structure of a pixel portion included in a display device used in the present invention will be described.

In the pixel portion, a plurality of pixels 73 are arranged in a matrix.
4 are arranged. An enlarged view of the pixel 734 is shown in FIG. The pixel 734 includes a first pixel TFT 735 and a second pixel TF
T736, SRAM 737, a liquid crystal cell 738 having liquid crystal interposed between a counter electrode and a pixel electrode, a first switch 73
1 and a second switch 732 are provided.

The gate electrode of the first pixel TFT 735 is connected to the gate signal line 739. Also, the first pixel T
One of the source region and the drain region of the FT735 is the first region.
The other end is connected to the source signal line 740 and the other end to the input side of the SRAM 737.

The gate electrode of the second pixel TFT 736 is connected to the gate signal line 739. Also, the second pixel T
One of the source region and the drain region of the FT 736 is the second region.
The other end is connected to the source signal line 741 and the output side of the SRAM 737.

The SRAM 737 is composed of a p-channel TFT and n
It has two channel type TFTs, and the source region of the p-channel type TFT is connected to the high voltage side power supply line 742 and is kept at the voltage Vddh. Also, n-channel type T
The source region of the FT is connected to the low-voltage power supply line 743 and is kept at the voltage Vss. Vddh> Vs
s. One p-channel TFT and one n-channel TFT are paired, and one SRAM has two pairs of p-channel TFTs and n-channel TFTs.

The drain regions of the paired p-channel TFT and n-channel TFT are connected to each other. The gate electrodes of the paired p-channel TFT and n-channel TFT are connected to each other. And a pair of p-channel and n-channel T
The drain region of the FT is kept at the same potential as the gate electrode of the other pair of p-channel and n-channel TFTs. The drain region of one pair of p-channel and n-channel TFTs is an input side to receive an input signal (Vin), and the drain region of the other pair of p-channel and n-channel TFTs is an output signal. (Vout)
Is the output side where is output.

The SRAM 737 holds Vin, and Vin
Is designed to output Vout, which is a signal obtained by inverting Vout. That is, if Vin is Hi, Vout becomes Vs
s, and if Vin is Lo, Vout
Is a Hi signal equivalent to Vddh.

On the other hand, the first switch 731 and the second switch 732 are transmission gates each having one p-channel TFT and one n-channel TFT. The gate electrode of the p-channel TFT of the first switch 731 and the n-channel TF of the second switch 732
The gate electrode of T is connected to the input side of the SRAM 737. The gate electrode of the n-channel TFT of the first switch 731 and the gate electrode of the p-channel TFT of the second switch 732 are connected to the SRAM 73.
7 is connected to the output side.

The input side of the first switch 731 is connected to the AC drive signal line 745, and the input side of the second switch 732 is connected to the reset signal line 746.

The output side of the first switch 731 and the output side of the second switch 732 are both connected to the pixel electrode of the liquid crystal cell 738.

The first pixel TFT 735 and the second pixel TFT 73 are driven by a selection signal input to the gate signal line 739.
6 are turned on. Digital video signals of opposite phases are input to the first source signal line 740 and the second source signal line 741, and the input digital video signals are S
It is held in the RAM 737.

[0108] On / off of the first switch 731 and the second switch 732 is selected according to the input digital video signal. When the first switch 731 is on, the second switch 732 is off. Conversely the first
When the switch 731 is off, the second switch 732 is on.

The reset signal line 746 is supplied with the same potential as that of the counter electrode of the liquid crystal cell.
5, an AC drive signal having a binary voltage, which is inverted with respect to the potential of the counter electrode, is input.

When the first switch 731 is turned on, the AC drive signal input to the AC drive signal line 745 is sampled and input to the pixel electrode of the liquid crystal cell 738 to display an image. Conversely, when the second switch 732 is turned on, the potential of the reset signal line 746 is input to the pixel electrode of the liquid crystal cell 738, and no image is displayed.

An SRAM requires less time to write a digital video signal than a DRAM, and can write data at a high speed. Accordingly, by providing an SRAM in a pixel in the present invention, a digital video signal input to a pixel can be held more reliably until the next digital video signal is input. That is, it is possible to prevent the charge held in the pixel electrode of the liquid crystal cell 738 from decreasing due to the leak current of the pixel TFT, and to prevent the amount of light transmitted through the liquid crystal cell from changing.

Note that a volatile memory can be formed using a TFT, and thus can be formed simultaneously with a pixel TFT.

In the present invention, the storage capacitor does not have to be provided positively. When the storage capacitor is not provided, the time for inputting the digital video signal to the pixel can be shortened. Therefore, even if the number of pixels of the liquid crystal display increases, the length of the writing period can be suppressed. (Example 4)

In this embodiment, a driving circuit of a display device used in the present invention will be described. FIG. 5A is a block diagram of a source signal line driver circuit.

A source signal line driving circuit includes a shift register circuit 761, a latch circuit A762, and a latch circuit B763.
have.

A clock signal (CK) and a start pulse (SP) are input to a shift register circuit 761 included in the source signal line driver circuit. Shift register circuit 761
Generates a timing signal in order based on the clock signal (CK) and the start pulse (SP), and sequentially supplies the timing signal to the latch circuit A762.

The latch circuit A762 has a plurality of latches for storing digital video signals. Latch circuit A
762, when the timing signal is input, sequentially captures and holds the digital video signal in each latch.

The time required to complete the writing of the digital video signal to all the latches of the latch circuit A762 is called a line period. Actually, a period in which the horizontal retrace period is added to the line period may be referred to as a line period.

After the end of one line period, the latch circuit B76
3 is supplied with a latch signal. At this moment, the digital video signal written and held in the latch circuit A762 is simultaneously sent to the latch circuit B763, and written and held in all the latches of the latch circuit B763.

A digital video signal is latched by a latch circuit B763.
The digital video signal is sequentially written again into the latch circuit A762 which has been transmitted to the latch circuit A762 based on the timing signal from the shift register circuit 761.

During the second line period, the digital video signals written and held in the latch circuit B763 are sequentially supplied to the source signal lines.

FIG. 5B is a block diagram of a gate signal line driver circuit. The gate signal line driver circuit includes a shift register circuit 766 and a buffer circuit 767. When a clock signal (CLK) and a start pulse signal (SP) are input to the shift register circuit 766 in the gate signal line driver circuit, a selection signal for controlling switching of the pixel TFT is generated. The selection signal is buffer-amplified in the buffer circuit 767 and input to the gate signal line.

This embodiment can be implemented in any combination with Embodiments 1 to 3.

Embodiment 5 In this embodiment, an example in which a liquid crystal display device is manufactured by using the present invention will be described with reference to FIGS.

FIG. 6A is a top view of a liquid crystal display device formed by sealing liquid crystal between a TFT substrate and a counter substrate, and FIG. 6B is a plan view of FIG. A-
FIG. 6C is a cross-sectional view taken along line A ′ of FIG.
It is sectional drawing in B '.

A sealing material 4009 is provided so as to surround the pixel portion 4002 provided over the TFT substrate 4001, the source signal line driving circuit 4003, and the first and second gate signal line driving circuits 4004a and 4004b. I have. A pixel portion 4002, a source signal line driver circuit 4003,
A counter substrate 4008 is provided over the first and second gate signal line driver circuits 4004a and 4004b. A liquid crystal 4210 is filled in a space surrounded by the TFT substrate 4001, the sealant 4009, and the counter substrate 4008.

The pixel portion 4002 provided on the TFT substrate 4001, the source signal line driving circuit 4003, and the first and second gate signal line driving circuits 4004a and 4004b have a plurality of TFTs. . In FIG. 6B, typically, a driving TFT included in the source signal line driving circuit 4003 formed on the base film 4010 (here, n
(A channel type TFT and a p-channel type TFT are shown.)
201 and a pixel TFT (TFT controlling a voltage applied to a pixel electrode) 4202 included in the pixel portion 4002 are illustrated.

In this embodiment, a p-channel TFT or an n-channel TFT manufactured by a known method is used for the driving TFT 4201, and a p-channel TFT manufactured by a known method is used for the pixel TFT 4202. .
The pixel portion 4002 is provided with a storage capacitor (not shown) connected to the gate of the pixel TFT 4202.

Drive TFT 4201 and Pixel TFT 420
2, an interlayer insulating film (planarization film) 4301 is formed,
A pixel electrode 4203 electrically connected to the drain of the pixel TFT 4202 is formed thereon.

An opposing electrode 4205 is provided on the opposing substrate 4008.
Are formed. Although not shown in the figure, a color filter and a polarizing plate are appropriately provided. A predetermined voltage is applied to the counter electrode 4205.

As described above, a liquid crystal cell including the pixel electrode 4203, the liquid crystal 4210, and the counter electrode 4205 is formed.

Reference numeral 4005 denotes a lead-out wiring, and the pixel portion 4
002, a source signal line driver circuit 4003, a first gate signal line driver circuit 4004a, a second gate signal line driver circuit 4004b, and an external power supply. The lead wiring 4005a is formed of a sealing material 4009 and a TFT substrate 400.
1 and is electrically connected to an FPC wiring 4301 included in the FPC 4006 via an anisotropic conductive film 4300.

As the opposing substrate 4008, a glass material, a metal material (typically, a stainless steel material), a ceramic material, and a plastic material (including a plastic film) can be used. As a plastic material, FRP (Fi
Berglass-Reinforced Plast
ics) plate, PVF (polyvinyl fluoride) film, mylar film, polyester film or acrylic resin film. Further, a sheet having a structure in which an aluminum foil is sandwiched between PVF films or mylar films can also be used.

However, when the light emission direction from the pixel electrode is directed toward the cover material, the cover material must be transparent. In that case, a transparent material such as a glass plate, a plastic plate, a polyester film or an acrylic film is used.

As shown in FIG. 6C, the pixel electrode 420
At the same time as the formation of the conductive film 4203, a conductive film 4203a is formed so as to be in contact with the lead wiring 4005a.

The anisotropic conductive film 4300 has a conductive filler 4300a. TFT substrate 400
1 and the FPC 4006 are thermocompression-bonded, so that the conductive film 4203a on the TFT substrate 4001 and the FPC wiring 4301 on the FPC 4006 become conductive filler 4300a.
Electrically connected by

This embodiment can be implemented by freely combining with Embodiments 1 to 4.

(Embodiment 6) In this embodiment, an external view of a portable information terminal of the present invention will be described. FIG. 7 shows a portable information terminal having the structure of the present invention, where 2701 is a display panel and 2702 is an operation panel. The display panel 2701 and the operation panel 2702 are connected to each other by a connection portion 2703.
Connected. The angle θ of the connection portion 2703 between the surface of the display panel 2701 on which the display portion 2704 is provided and the surface of the operation panel 2702 on which the operation keys 2706 are provided can be arbitrarily changed.

[0139] The display panel 2701 has a display portion 2704. The portable information terminal shown in FIG. 7 has a function as a telephone, the display panel 2701 has an audio output unit 2705, and the audio is output from the audio output unit 2705.
Output from A liquid crystal display device is used for the display portion 2704.

The operation panel 2702 has an operation key 270
6, a power switch 2707 and a voice input unit 2708. Although the operation key 2706 and the power switch 2707 are separately provided in FIG. 7, a configuration in which the power switch 2707 is included in the operation key 2706 may be employed. In the voice input unit 2708, voice is input.

In FIG. 7, the display panel 2701 has the audio output unit 2705 and the operation panel 2702 has the audio input unit 2708, but this embodiment is not limited to this configuration. The display panel 2701 is a voice input unit 270
8 and the operation panel may have a sound output unit 2705. The audio output unit 2705 and the audio input unit 27
08 may be provided on the display panel 2701, or both the audio output unit 2705 and the audio input unit 2708 may be provided on the operation panel 2702.

FIG. 8 shows an example in which the operation key 2706 of the portable information terminal shown in FIG. 7 is operated with the index finger. FIG. 9 shows an example in which the operation key 2706 of the portable information terminal shown in FIG. 7 is operated with the thumb.
Note that the operation key 2706 may be provided on a side surface of the operation panel 2702. Operation is only with one hand (kind hand) forefinger,
Or even with just the thumb.

This embodiment can be implemented by freely combining with Embodiments 1 to 5.

(Embodiment 7) In this embodiment, a portable information terminal having a portable device different from that shown in Embodiment 6 will be described. FIG. 10 is an external view of the portable information terminal according to the present embodiment. FIG. 10A is a top view, and FIG. 10B is a side view.

Reference numeral 2901 denotes a display panel, and 2902 denotes an operation panel. The display panel 2901 and the operation panel 2902 are connected at a connection portion 2903.
The display panel 2901 in the connection portion 2903
Of the display panel 2904 and the operation panel 2
The angle between the operation key 902 and the surface on which the operation keys 2906 are provided can be arbitrarily changed.

The display panel 2901 has a display section 2904. Further, the portable information terminal shown in FIG. 10 has a function as a telephone, the display panel 2901 has a voice output unit 2905,
5 is output. For the display portion 2904, a liquid crystal display device having the structure of the present invention is used.

The display unit 2904 has an aspect ratio of 16:
9, 4: 3, etc. can be arbitrarily selected. Display 2
The size of 904 is desirably about 1 inch to 4.5 inches diagonally.

The operation panel 2902 has an operation key 290
6, a power switch 2907 and a voice input unit 2908. Although the operation key 2906 and the power switch 2907 are provided separately in FIG. 10, a configuration in which the power switch 2907 is included in the operation key 2906 may be employed.
In the voice input unit 2908, voice is input.

[0149] Further, the image from the CCD light receiving section 2910 can be taken into the portable information terminal as electronic information.

Reference numeral 2911 denotes an external connection port, which can take in data from the outside. 290
9 is an antenna.

In FIG. 10, the display panel 2901 has the audio output unit 2905 and the operation panel 2902 has the audio input unit 2908; however, the present embodiment is not limited to this configuration. The display panel 2901 is a voice input unit 29
08, and the operation panel may include the audio output unit 2905. The audio output unit 2905 and the audio input unit 2
908 may be provided on the display panel 2901, or the sound output unit 2905 and the sound input unit 2908 may be both provided on the operation panel 2902.

In the portable information terminal shown in FIG. 10, operation keys 2906 each have an LED, a liquid crystal, an EL, or the like. Then, one or more characters, symbols, numerals, and the like are displayed on each of the operation keys 2906 by using an LED, a liquid crystal, an EL, or the like included in each of the operation keys 2906. The portable information terminal of the present embodiment has a display unit 2904
The user can appropriately change the direction of the image displayed on the operation key 2906 and the direction of the image such as characters, numerals, and symbols displayed on the operation keys 2906.

In FIG. 10A, when the display panel 2901 and the operation panel 2902 are arranged side by side, the direction of the image displayed on the display portion 2904 and the operation key 290 are displayed.
The direction of the image of characters, numbers, symbols, etc. displayed in 6 is
The case where the user is in the original direction as viewed from the user is shown.

Although not shown, the display panel 2
When the screen 901 and the operation panel 2902 are arranged vertically, the direction of the image displayed on the display unit 2904 and the direction of the image such as characters, numbers, and symbols displayed on the operation keys 2906 are determined by the user. It may be in the original direction as viewed from the side.

According to the portable information terminal of the present invention, the direction of the image displayed on the display portion 2904 and the direction of the image such as characters, numbers, and symbols displayed on the operation keys 2906 can be switched according to the user's convenience. Is possible.

In FIG. 10, the direction of the image displayed on the display unit 2904, the characters displayed on the operation keys 2906,
Although the case where the directions of the images such as numbers and symbols are always the same has been described, the present invention is not limited to this. Display unit 290
The direction of the image displayed on the operation key 2906 may be different from the direction of the image displayed on the operation key 2906.

The characters, numbers and symbols displayed by the operation keys shown in FIG. 10 are examples, and the portable information terminal of the present invention is not limited to these characters, numbers and symbols.

The display unit 2904 of the display panel 2901 in the connection unit 103 has the direction of the image displayed on the display unit 2904 and the direction of the image such as characters, numbers, and symbols displayed on the operation keys 2906. A configuration may be employed in which switching is automatically performed according to the angle between the surface and the surface of the operation panel 2902 having the operation keys 2906. These configurations are described in Patent Application 2000-080973.
Is described in detail.

With the above configuration, the portable information terminal of the present invention can be made more convenient for the user.

This embodiment can be implemented by freely combining with Embodiments 1 to 5.

Embodiment 8 In this embodiment, an example in which a memory circuit provided in a pixel portion is provided below a source signal line will be described.

FIG. 16 is a top view of a pixel of a transmission type liquid crystal display device. The pixel 801 is connected to one of the source signal lines 804
One is a region including the gate signal line 803, and has a pixel electrode 801. Although not shown in FIG. 16, the pixel 800 has a pixel TFT for controlling a voltage applied to the pixel electrode 801 based on a digital video signal input to a source signal line.

The design rule is 1 μm and the pixel pitch is 1
With about 00 ppi, the memory circuit used in the present invention can be arranged below the source signal line 804, and can be applied not only to a reflection type but also to a transmission type liquid crystal display device.

Further, a memory circuit can be provided below the gate signal line 803 instead of the source signal line 804.

This embodiment can be implemented by freely combining with Embodiments 1 to 7.

[0166]

According to the present invention, a digital video signal is stored by using a plurality of storage circuits disposed inside each pixel.
It is possible to repeatedly use the digital video signal stored in the storage circuit in each frame period when displaying a still image, and to stop the source signal line drive circuit when displaying a still image continuously Becomes Therefore, it is possible to greatly contribute to lower power consumption of the entire liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a portable information terminal of the present invention.

FIG. 2 is a block diagram showing a configuration of a mobile phone according to the present invention.

FIG. 3 is a pixel circuit diagram of a display device of the present invention.

FIG. 4 is a pixel circuit diagram of a display device of the present invention.

FIG. 5 is a block diagram of a drive circuit of a display device of the present invention.

FIG. 6 is a top view and a cross-sectional view of a display device of the present invention.

FIG. 7 is an external view of a mobile phone having the configuration of the present invention.

FIG. 8 is an external view of a mobile phone having the structure of the present invention.

FIG. 9 is an external view of a mobile phone having the configuration of the present invention.

FIG. 10 is an external view of a mobile phone having the structure of the present invention.

FIG. 11 is a block diagram showing a configuration of a conventional portable information terminal.

FIG. 12 is a block diagram showing a configuration of a conventional mobile phone.

FIG. 13 is a block diagram illustrating a configuration of a transmission / reception circuit.

FIG. 14 is a block diagram of a conventional display device.

FIG. 15 is a pixel circuit diagram of a conventional display device.

FIG. 16 is a top view of a pixel of a display device of the present invention.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G09G 3/20 621 G09G 3/20 621M 624 624B 631 631H 660 660U 680 680G 680Q 680S 680T F3022FA08 MA20 2H093 NA16 NC22 NC26 NC34 NC50 ND39 5C006 AA01 AA02 AF03 AF04 AF44 BB16 BC03 BC06 BC12 BC20 BF02 BF04 BF09 BF15 EB05 FA47 5C080 AA06 AA10 BB05 DD25 DD26 EE17 FF11 GG07 GG08 GG12 JJ06 KK02 JJ02 KK06

Claims (20)

[Claims] 1. A portable information device having a display device and a controller, wherein the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and a video signal written to the storage circuit. A portable information device, wherein a voltage applied to the liquid crystal cell is controlled, and writing of a video signal to the storage circuit is controlled by the controller. 2. A portable information device having a display device and a controller, wherein the display device includes a plurality of pixels each including a storage circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to the liquid crystal cell. The video signal written to the storage circuit,
The portable information device, wherein switching of FT is controlled, and writing of a video signal to the storage circuit is controlled by the controller. 3. The portable information device according to claim 1, wherein the controller includes a clock generation circuit. 4. A portable information device having a display device and a CPU, wherein the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and is provided with a video signal written in the storage circuit. A portable information device, wherein a voltage applied to the liquid crystal cell is controlled, and writing of a video signal to the storage circuit is controlled by the CPU. 5. A portable information device having a display device and a CPU, wherein the display device includes a plurality of pixels each including a storage circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to the liquid crystal cell. The video signal written to the storage circuit,
A portable information device, wherein FT switching is controlled, and writing of a video signal to the storage circuit is controlled by the CPU. 6. A portable information device having a display device, wherein the display device has a plurality of pixels, the plurality of pixels has a storage circuit and a liquid crystal cell, and among the plurality of pixels, A portable information device including means for rewriting data stored in a storage circuit included in a pixel in a specific row or column. 7. A portable information device having a display device, wherein the display device has a plurality of pixels, and the plurality of pixels control a storage circuit, a liquid crystal cell, and a voltage applied to the liquid crystal cell. A portable information device, comprising: a TFT; and means for rewriting data stored in a storage circuit included in a pixel in a specific row or column among the plurality of pixels. 8. The portable information device according to claim 1, wherein the portable information device is a mobile phone, a personal computer, a navigation system, a PDA, or an electronic book. 9. A driving method of a portable information device having a display device and a controller, wherein the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and the display device displays a still image. And stopping a video display function other than the display device and the controller. 10. A method for driving a portable information device having a display device and a controller, wherein the display device includes a storage circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode included in the liquid crystal cell. A method for driving a portable information device, comprising a plurality of pixels, wherein a video display function other than the display device and the controller is stopped when the display device displays a still image. 11. The method according to claim 9, wherein the controller is a clock generation circuit of a display device. 12. A method for driving a portable information device having a display device, wherein the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and when the display device displays a still image, A method for driving a portable information device, wherein a signal having video information is not input to the display device from outside the display device. 13. A driving method of a portable information device having a display device, wherein the display device includes a plurality of pixels each including a storage circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode of the liquid crystal cell. A method for driving a portable information device, comprising: when the display device displays a still image, a signal having video information is not input to the display device from outside the display device. 14. A method for driving a portable information device having a display device and a CPU, wherein the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and the display device displays a still image. A method for driving a portable information device, wherein the image display function of the CPU is stopped when displaying. 15. A method for driving a portable information device having a display device and a CPU, wherein the display device includes a storage circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode of the liquid crystal cell. A method for driving a portable information device, comprising: a plurality of pixels including: when the display device displays a still image, the image display function of the CPU is stopped. 16. A method for driving a portable information device having a display device and a VRAM, wherein the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and the display device displays a still image. A method for driving a portable information device, comprising: stopping display of data stored in the VRAM when displaying. 17. A method for driving a portable information device including a display device and a VRAM, wherein the display device includes a storage circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode included in the liquid crystal cell. A method for driving a portable information device, comprising: stopping calling of data stored in the VRAM when the display device displays a still image. 18. A method for driving a portable information device having a display device, wherein the display device has a plurality of pixels each including a storage circuit and a liquid crystal cell, and the display device displays a still image. And a method of driving a portable information device, comprising: stopping a source signal line driving circuit of the display device. 19. A method for driving a portable information device having a display device, the display device comprising: a plurality of memory devices each including a storage circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode of the liquid crystal cell. A driving method of a portable information device, comprising a pixel, wherein a source signal line driving circuit of the display device is stopped when the display device displays a still image. 20. The method according to claim 9, wherein the storage circuit is called once in one frame period.