JP2012181540A - Portable information device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the consumption power of a portable information device.SOLUTION: A portable information device includes a display device, a CPU, and an external input terminal, in which the display device includes a source signal line drive circuit and a plurality of pixels, and the plurality of pixels each include a circuit having the function of storing video signals input to the pixel and a pixel electrode. And, if the input of signals for changing a video display is not performed by the external input terminal for a certain period, the CPU determines that the display device displays a still picture, and when the display device displays the still picture, the supply of a start pulse, a clock signal, and a video data signal is stopped from the CPU to the source signal line drive circuit.

Description

  The present invention relates to a portable information device and a driving method thereof, and in particular, a mobile phone, a PDA (Personal Digital Assistant), a portable personal computer, a portable game device, a portable navigation system, an electronic book, and the like having a flat display using liquid crystal. The present invention relates to a portable information device.

  In recent years, mobile phones have become popular due to the development of communication technology. In the future, more video transmission and more information transmission are expected. On the other hand, personal computers are also being produced with mobile-friendly products due to their light weight. A large number of information devices called personal digital assistants, beginning with electronic notebooks, have been produced and are becoming popular. In addition, with the development of liquid crystal display devices and the like, most of these portable devices are equipped with a flat display.

  As a more recent technology, active matrix display devices have begun to be used in these portable devices. In an active matrix display device, one TFT is arranged for each pixel, and the screen is controlled by the TFT. Such an active matrix display device has advantages such as higher resolution of images, improved image quality, and compatibility with moving images, as compared with a passive matrix display device. Therefore, in the future, the display device of portable information equipment will change from a passive matrix type to an active matrix type.

  In addition, among active matrix display devices, display devices using low-temperature polysilicon have been commercialized in recent years. With the low-temperature polysilicon technology, in addition to the pixel TFT constituting the pixel, a driving circuit can be simultaneously formed in the peripheral portion of the pixel portion using the TFT. Therefore, a liquid crystal display device (a display device having a liquid crystal cell) is indispensable for a display unit of a mobile device that has greatly contributed to downsizing and low power consumption of the device, and whose application field has been remarkably expanded in recent years. It has become a device.

  FIG. 11 shows a block diagram of a conventional portable information terminal. Reference numeral 1204 denotes a power source. In the portable information terminal, it is required to extract information requested by the user as necessary. The information includes information stored in a storage device (DRAM 1209, flash memory 1210, etc.) in the portable information terminal, information stored in a memory card 1203 inserted into the portable information terminal, and via an external interface port 1205. Some can be obtained by connecting to external devices.

  A user's instruction input from the pen input tablet 1201 is read as electronic information in the detection circuit 1202. The electronic information is sent to the video signal processing circuit 1207 by the tablet interface 1218. 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 mobile phone. Those already illustrated in the portable information terminal shown in FIG.

  The cellular phone includes a transmission / reception circuit 1224 for transmitting / receiving radio waves, an audio processing circuit 1221 for processing audio signals received, a speaker 1223, a microphone 1222, a keyboard 1220 for inputting data, a display device 1213 for displaying, an LCD controller 1212 for the display, It consists of storage devices (VRAM 1211, DRAM 1209, flash memory 1210, etc.).

  In the mobile phone shown in FIG. 12, the operations of the keyboard interface 1238, the video signal processing circuit 1207, the VRAM 1211, and the LCD controller 1212 are the same as those in the mobile 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 by the antenna 1302. The filter 1303 extracts only necessary data from the electronic information and inputs the data to the amplifier 1305 via the switch 1304. Data input to the amplifier 1305 is amplified and input to the filter 1307. Data from which unnecessary information is cut by the filter 1303 is increased in frequency by the first frequency conversion circuit 1309 and input to the filter 1312.

  Data whose unnecessary information is cut by the filter 1312 is increased in frequency again by the second frequency conversion circuit 1313 and input to the filter 1316.

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

  The data demodulating circuit 1318 solves the encoded data and inputs it 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 the frequency of the encoded data is increased, and the encoded data is input to the frequency converter circuit 1311.

  The data input to the frequency conversion circuit 1311 is input to the filter 1308 with the frequency increased. Data from which unnecessary information is cut by the filter 1308 is amplified by the amplifier 1306 and input to the filter 1303 via the switch 1304.

  Data from which unnecessary information is cut by the filter 1303 is transmitted by the antenna 1302.

  A schematic view of a display device having a liquid crystal cell driven by a conventional digital method is shown in FIG. In the display device, a pixel portion 9003, a source signal line driver circuit 9001, and a gate signal line driver circuit 9002 are arranged.

  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 A 9001-2, a latch circuit B 9001-3, and a D / A conversion circuit 9001-4. The gate signal line driver circuit 9002 includes a shift register circuit 9002-1 and a buffer circuit 9002-1.

  FIG. 15 shows a circuit diagram of the pixel 9004. The pixel 9004 includes one source signal line 9005 and one gate signal line 9006. The pixel 9004 is provided with a pixel TFT 9007, a liquid crystal cell 9008 in which liquid crystal is sandwiched between the counter electrode and the pixel electrode, and a capacitor 9009.

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

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

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

  A clock signal (CK) and a start pulse (SP) are input to the shift register circuit 9001-1 included in the source signal line driver circuit 9001. The shift register circuit 9001-1 sequentially generates timing signals based on the clock signal (CK) and the start pulse (SP), and sequentially supplies the timing signals to the latch circuit A 9001-2.

  The latch circuit A9001-2 has a plurality of latches for storing digital video signals. When the timing signal is input, the latch circuit A 9001-2 sequentially captures and holds the digital video signal in each latch.

  The time until writing of the digital video signal to all the latches of the latch circuit A9001-2 is called a line period. Actually, a period obtained by adding a horizontal blanking period to the line period may be called a line period.

  After the end of one line period, a latch signal (Latch Signal) is supplied to the latch circuit B9001-3. At this moment, the digital video signals written and held in the latch circuit A9001-2 are sent all at once to the latch circuit B9001-3, and are written and held in all the latches of the latch circuit B9001-3.

  Based on the timing signal from the shift register circuit 9001-1, the digital video signal is sequentially written again to the latch circuit A9001-2 that has finished sending the digital video signal to the latch circuit B9001-3.

  During the second 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.

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

  On the other hand, when a clock signal (CLK) and a start pulse signal (SP) are input to the shift register circuit 9002-1 in the gate signal line driver circuit 9002, a selection signal for controlling switching of the pixel TFT 9007 is generated. The selection signal is buffered and 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, and the analog video signal input to the source signal line is input to the pixel electrode of the liquid crystal cell 9008 through the pixel TFT.

  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 the 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.

  One image is displayed by performing the above operation in each pixel.

  In the conventional information terminal device as described above, when the display screen is displayed, even if the screen is a still screen, the same video data is continuously sent to the display device 60 times per second. It was. In other words, the video signal processing circuit 1207, the VRAM 1211, the controller 1212, and the display signal 1213 included in the CPU 1206 operate as long as display is performed as long as display is performed.

  Some passive display devices with a small number of pixels include a memory built in the driver IC or LCD controller of the display device and stop the VRAM, but a display device using a large number of pixels such as an active matrix. Then, it is unrealistic to have a memory in the driver or the controller from the viewpoint of the chip size. Therefore, in the conventional information terminal device, even when a still image is displayed, many circuits must continue to operate, which hinders reduction in power consumption.

  In portable information terminals, low power consumption is highly desired. In addition, in this mobile device, although it is mostly used in the still image mode, the drive circuit continues to operate even when displaying a still image as described above. This is a drag on power consumption.

  In view of the above-described problems, an object of the present invention is to reduce power consumption of a driving circuit when a still image is displayed by using a novel circuit.

  In order to solve the above-described problems, the present invention uses the following means.

A plurality of storage circuits are arranged in the pixel, and a digital video signal is stored for each pixel.
In the case of a still image, once writing is performed, the information written to the pixels thereafter is the same. Therefore, by reading the signal stored in the storage circuit without inputting the signal every frame, Can be displayed continuously. In other words, when displaying a still image, it is possible to stop the source signal line drive circuit after performing a signal processing operation for at least one frame, thereby greatly reducing power consumption. Is possible.

  The configuration of the liquid crystal display device of the present invention will be described below.

  According to the present invention, in the 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, the display device A portable information device is provided that stops video display functions other than the controller.

  According to the present invention, in the portable information device having a display device and a controller, the display device has a plurality of pixels each including a memory circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode of the liquid crystal cell. When the display device displays a still image, a portable information device is provided that stops video display functions other than the display device and the controller.

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

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

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

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

  According to the present invention, in the portable information device having a display device and a CPU, the display device has a plurality of pixels each including a memory circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode of the liquid crystal cell. When the display device displays a still image, a portable information device is provided that stops the video display function of the CPU.

  According to the present invention, in the portable information device having a display device and a VRAM, the display device has a plurality of pixels each including a memory circuit and a liquid crystal cell, and when the display device displays a still image, the VRAM There is provided a portable information device characterized in that the calling of the data stored in 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 memory circuit, a liquid crystal cell, and a TFT for controlling a voltage applied to a pixel electrode of the liquid crystal cell. And when the said display apparatus displays a still image, the call of the data memorize | stored in the said VRAM is stopped, The portable information apparatus characterized by the above-mentioned is provided.

  According to the present invention, in the portable information device having a display device, the display device has a plurality of pixels each including a memory circuit and a liquid crystal cell, and when the display device displays a still image, the source of the display device A portable information device characterized by stopping the signal line driver circuit is provided.

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

  The storage circuit may be called once per frame period.

  According to the present invention, in the portable information device having a display device, the display device includes a plurality of pixels, the plurality of pixels includes a memory circuit and a liquid crystal cell, and a specific row of the plurality of pixels is selected. Alternatively, a portable information device including means for rewriting data stored in a memory circuit included in a column of pixels is provided.

  According to the present invention, in the portable information device having a display device, the display device includes a plurality of pixels, and the plurality of pixels controls a voltage applied to a memory circuit, a liquid crystal cell, and a pixel electrode included in the liquid crystal cell. There is provided a portable information device comprising means for rewriting data stored in a memory circuit included in a pixel in a specific row or column among the plurality of pixels.

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

  By storing digital video signals using a plurality of storage circuits arranged inside each pixel, the digital video signals stored in the storage circuit are repeatedly used in each frame period when displaying a still image. When the still image is continuously displayed, the source signal line driver circuit can be stopped. Therefore, it can greatly contribute to the reduction in power consumption of the entire liquid crystal display device.

The block diagram which shows the structure of the portable information terminal of this invention. 1 is a block diagram illustrating a configuration of a mobile phone according to the present invention. FIG. 6 is a pixel circuit diagram of a display device of the present invention. FIG. 6 is a pixel circuit diagram of a display device of the present invention. FIG. 6 is a block diagram of a driver circuit of a display device of the present invention. The top view and sectional drawing of the display apparatus of this invention. 1 is an external view of a mobile phone having the configuration of the present invention. 1 is an external view of a mobile phone having the configuration of the present invention. 1 is an external view of a mobile phone having the configuration of the present invention. 1 is an external view of a mobile phone having the configuration of the present invention. The block diagram which shows the structure of the conventional portable information terminal. The block diagram which shows the structure of the conventional mobile telephone. The block diagram which shows the structure of a transmission / reception circuit. The block diagram of the conventional display apparatus. FIG. 6 is a pixel circuit diagram of a conventional display device. FIG. 6 is a top view of a pixel of a display device of the present invention.

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. Therefore, it is possible to display a still image without driving the source signal line driver circuit in the video signal processing circuit 2107, the VRAM 2111, and the display device 2213 among the internal circuits of the CPU 2106 that have been operated conventionally. Become. Note that information required by the user as needed can be extracted from the external device via the external interface port 2105.
In addition, information stored in the memory card 2103 inserted into the portable information terminal can be extracted. Reference numeral 2104 denotes a power source.

  The contents will be specifically described below.

  When the input from the pen input tablet 2101 is not performed for a certain period of time, or when the signal input that requires the video display to be changed from the external input terminal is not performed for a certain period of time, the CPU 2106 determines that the still image mode is set.

  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, clock signal, and 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 supply and supplies 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, when using a liquid crystal material that does not cause image quality problems of the liquid crystal display device, for example, a burn-in phenomenon, the gate signal line driver circuit may be stopped. By 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, there is no need to newly send video data to the display device 2213 when displaying a still image. . Therefore, the video signal processing circuit 2107 for generating and processing video data, the tablet interface 2118, the VRAM 2111, and the like do not have to operate. Further, it is not necessary to access storage circuits such as the DRAM 2109 and the flash memory 2110 that hold information requested 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 driver circuit are achieved.

  When a signal is input again from an external input terminal such as the pen input tablet 2101, the detection circuit 2102 of the pen input tablet 2101 instructs the CPU 2106 to change the display content. Then, the CPU 2106 operates the stopped VRAM 2111, tablet interface 2118, and video signal processing circuit 2107. Then, a start pulse, a clock signal, and video data can be supplied to the source signal line driver circuit of the display device 2213 via the LCD controller 2112, and a new video signal can be written into the pixel.

  FIG. 2 is an example of a mobile phone using the present invention. The outline of the operation is almost the same as that of the portable information terminal of FIG. Unlike a mobile information terminal, in a mobile phone, input is performed by a keyboard, and external data is input to an antenna through a communication system of a telephone company and amplified by a transmission / reception circuit shown in FIG. After that, it is controlled by the CPU and put on the display device. In the case of displaying a still image, the video signal processing circuit, the VRAM, the source signal line driver circuit, and the like can be stopped as in the portable information terminal.

  Examples of the present invention will be described below.

  In this embodiment, a structure of a mobile phone having the structure of the present invention will be described.

  FIG. 2 shows a block diagram of the mobile phone of this embodiment. Those already illustrated in the portable information terminal shown in FIG.

  The cellular phone includes a transmission / reception circuit 2124 for transmitting / receiving radio waves, an audio processing circuit 2121 for processing audio signals received, a speaker 2123, a microphone 2122, a keyboard 2120 for inputting data, a display device 2113 for displaying data, an LCD controller 2112 for the same, It consists of storage devices (VRAM 2111, DRAM 2109, flash memory 2110, etc.).

  In the mobile phone shown in FIG. 2, the operations of the keyboard interface 2138, the video signal processing circuit 2107, the VRAM 2111 and the LCD controller 2112 are the same as those in the mobile information terminal shown in FIG. The only difference is that the user's instructions are read as electronic information on the keyboard 2120. Data from the outside is input to the antenna via the communication system of the telephone company, amplified by the transmission / reception circuit 2224 shown in FIG. 2, then 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 the signal input that requires the video display to be changed from the external input terminal is not performed for a certain period of time, the CPU 2106 determines that the still image mode is set.

  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, clock signal, and 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 supply, and supplies data of a memory circuit provided in a pixel portion in the display device 2213 to the 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, when using a liquid crystal material that does not cause image quality problems of the liquid crystal display device, for example, a burn-in phenomenon, the gate signal line driver circuit may be stopped. By 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, there is no need to newly send video data to the display device 2213 when displaying a still image. . Therefore, the video signal processing circuit 2107 that generates and processes video data, the keyboard interface 2138, the VRAM 2111, and the like do not have to operate. Further, it is not necessary to access storage circuits such as the DRAM 2109 and the flash memory 2110 that hold information requested 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 driver circuit are achieved.

  In addition, when a signal is input again from an external input terminal such as the keyboard 2220, the keyboard 2220 instructs the CPU 2106 to change the display contents. Then, the CPU 2106 operates the stopped VRAM 2111, keyboard interface 2138, and video signal processing circuit 2107. Then, a start pulse, a clock signal, and video data can be supplied to the source signal line driver circuit of the display device 2213 via the LCD controller 2112, and a new video signal can be written into the pixel.

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

  A plurality of pixels 704 are arranged in a matrix in the pixel portion. An enlarged view of the pixel 704 is shown in FIG. The pixel 704 is provided with a pixel TFT 705, an SRAM 707, and a liquid crystal cell 708 with a liquid crystal sandwiched between the counter electrode and the pixel electrode.

  A gate electrode of the pixel TFT 705 is connected to the gate signal line 709. One of the source region and the drain region of the pixel TFT 705 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 two p-channel TFTs and two n-channel TFTs, and the source region of the p-channel TFT is connected to the high voltage side power supply line 711 and is maintained at the voltage Vddh. The source region of the n-channel TFT is connected to the low voltage side power supply line 712 and is kept at the voltage Vss. Note that Vddh> Vss. One p-channel TFT and one n-channel TFT are paired, and two pairs of p-channel TFT and n-channel TFT exist in one SRAM.

  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. The drain regions of one pair of p-channel and n-channel TFTs are maintained at the same potential as the gate electrodes 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 for receiving an input signal (Vin), and the drain region of the other pair of p-channel and n-channel TFTs is an output signal. This is the output side where (Vout) is output.

  The SRAM is designed to hold Vin and output Vout that is a signal obtained by inverting Vin. That is, when Vin is Hi, Vout is a Lo signal corresponding to Vss, and when Vin is Lo, Vout is a Hi signal corresponding to Vddh.

  The output side of the SRAM 707 is connected to the pixel electrode included in the liquid crystal cell 708.

  The pixel TFT 705 is turned on by a 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. SRAM requires less time for writing a digital video signal than DRAM, and can write data at high speed.

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

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

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

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

  In the present invention, by providing the SRAM in the pixel, the digital video signal input to the pixel can be more reliably held 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 since a volatile memory can be formed using a TFT, it can be formed at the same time as the pixel TFT.

  In the present invention, the storage capacitor does not have to be positively provided. 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 device is increased, the length of the writing period can be suppressed.

  Note that this embodiment can be freely combined with the configuration shown in Embodiment 1.

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

  A plurality of pixels 734 are arranged in a matrix in the pixel portion. An enlarged view of the pixel 734 is shown in FIG. The pixel 734 is provided with a first pixel TFT 735, a second pixel TFT 736, an SRAM 737, a liquid crystal cell 738 having a liquid crystal sandwiched between a counter electrode and a pixel electrode, a first switch 731 and a second switch 732. It has been.

  The gate electrode of the first pixel TFT 735 is connected to the gate signal line 739. One of the source region and the drain region of the first pixel TFT 735 is connected to the first source signal line 740, and the other is connected 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. One of the source region and the drain region of the second pixel TFT 736 is connected to the second source signal line 741 and the other is connected to the output side of the SRAM 737.

  The SRAM 737 has two p-channel TFTs and two n-channel TFTs, and the source region of the p-channel TFT is connected to the high voltage side power supply line 742 and kept at the voltage Vddh. The source region of the n-channel TFT is connected to the low voltage side power line 743 and is kept at the voltage Vss. Note that Vddh> Vss. One p-channel TFT and one n-channel TFT are paired, and two pairs of p-channel TFT and n-channel TFT exist in one SRAM.

  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. The drain regions of one pair of p-channel and n-channel TFTs are maintained at the same potential as the gate electrodes 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 for receiving an input signal (Vin), and the drain region of the other pair of p-channel and n-channel TFTs is an output signal. This is the output side where (Vout) is output.

  The SRAM 737 is designed to hold Vin and output Vout which is a signal obtained by inverting Vin. That is, when Vin is Hi, Vout is a Lo signal corresponding to Vss, and when Vin is Lo, Vout is a Hi signal corresponding 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 included in the first switch 731 and the gate electrode of the n-channel TFT included in the second switch 732 are connected to the input side of the SRAM 737. Further, the gate electrode of the n-channel TFT included in the first switch 731 and the gate electrode of the p-channel TFT included in the second switch 732 are connected to the output side of the SRAM 737.

  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 736 are turned on by a selection signal input to the gate signal line 739. Opposite phase digital video signals are input to the first source signal line 740 and the second source signal line 741, and the input digital video signals are held in the SRAM 737.

  Further, on or 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, when the first switch 731 is off, the second switch 732 is on.

  The reset signal line 746 is supplied with the same potential as the counter electrode of the liquid crystal cell, and the AC drive signal line 745 receives an AC drive signal having a binary voltage that is inverted with respect to the potential of the counter electrode. ing.

  When the first switch 731 is 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, and an image is displayed. Conversely, when the second switch 732 is 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.

  SRAM takes less time to write a digital video signal than DRAM and can write data at high speed. Therefore, by providing the SRAM in the pixel in the present invention, the digital video signal input to the pixel can be more reliably held 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 being reduced by the leak current of the pixel TFT, and to prevent the transmitted light amount of the liquid crystal cell from changing.

  Note that since a volatile memory can be formed using a TFT, it can be formed at the same time as the pixel TFT.

  In the present invention, the holding capacitor does not have to be provided actively. 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.

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

  The source signal line driver circuit includes a shift register circuit 761, a latch circuit A762, and a latch circuit B763.

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

  The latch circuit A 762 includes a plurality of latches that store digital video signals. When the timing signal is input, the latch circuit A 762 sequentially captures and holds the digital video signal in each latch.

  The time until writing of the digital video signal to all the latches of the latch circuit A 762 is completed is called a line period. Actually, a period obtained by adding a horizontal blanking period to the line period may be called a line period.

  After the end of one line period, a latch signal (Latch Signal) is supplied to the latch circuit B763. At this moment, the digital video signals written and held in the latch circuit A 762 are sent all at once to the latch circuit B 763 and written and held in all the latches of the latch circuit B 763.

  Based on the timing signal from the shift register circuit 761, the digital video signal is sequentially written again in the latch circuit A 762 that has finished sending the digital video signal to the latch circuit B 763.

  During the second line period, the digital video signals written and held in the latch circuit B 763 are sequentially supplied to the source signal lines.

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

  In addition, a present Example can be implemented combining freely with Examples 1-3.

  In this embodiment, an example of manufacturing a liquid crystal display device 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 cross-sectional view of FIG. FIG. 6C is a cross-sectional view taken along the line BB ′ of FIG. 6A.

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

  In addition, the pixel portion 4002, the source signal line driver circuit 4003, and the first and second gate signal line driver circuits 4004a and 400b provided over the TFT substrate 4001 have a plurality of TFTs. In FIG. 6B, typically, a driving TFT (here, an n-channel TFT and a p-channel TFT are illustrated) 4201 formed over the base film 4010 and included in the source signal line driver circuit 4003; A pixel TFT (TFT for controlling a voltage applied to a pixel electrode) 4202 included in the pixel portion 4002 is 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. In addition, the pixel portion 4002 is provided with a storage capacitor (not shown) connected to the gate of the pixel TFT 4202.

  An interlayer insulating film (planarization film) 4301 is formed over the driving TFT 4201 and the pixel TFT 4202, and a pixel electrode 4203 electrically connected to the drain of the pixel TFT 4202 is formed thereon.

  A counter electrode 4205 is formed over the counter substrate 4008. Although not shown in the figure circle, a color filter and a polarizing plate are provided as appropriate. 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 wiring, which connects the pixel portion 4002, the source signal line driver circuit 4003, the first gate signal line driver circuit 4004a, and the second gate signal line driver circuit 4004b to an external power source. The lead wiring 4005 a passes between the sealant 4009 and the TFT substrate 4001 and is electrically connected to the FPC wiring 4301 included in the FPC 4006 through the anisotropic conductive film 4300.

  As the counter substrate 4008, a glass material, a metal material (typically a stainless steel material), a ceramic material, or a plastic material (including a plastic film) can be used. As the plastic material, an FRP (Fiberglass-Reinforced Plastics) plate, a PVF (polyvinyl fluoride) film, a mylar film, a polyester film, or an acrylic resin film can be used. 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 radiation direction of light 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 conductive film 4203a is formed so as to be in contact with the lead wiring 4005a at the same time as the pixel electrode 4203 is formed.

  The anisotropic conductive film 4300 has a conductive filler 4300a. By thermally pressing the TFT substrate 4001 and the FPC 4006, the conductive film 4203a on the TFT substrate 4001 and the FPC wiring 4301 on the FPC 4006 are electrically connected by the conductive filler 4300a.

  Note that this embodiment can be freely combined with Embodiments 1 to 4.

  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 configuration of the present invention, 2701 is a display panel, and 2702 is an operation panel. The display panel 2701 and the operation panel 2702 are connected at a connection portion 2703. In the connection portion 2703, the angle θ 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 key 2706 is provided can be arbitrarily changed.

  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 audio is output from the audio output unit 2705. A liquid crystal display device is used for the display portion 2704.

  The operation panel 2702 has operation keys 2706, a power switch 2707, and a voice input unit 2708. In FIG. 7, the operation key 2706 and the power switch 2707 are provided separately, but the operation key 2706 may include the power switch 2707. The voice input unit 2708 inputs voice.

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

  Note that FIG. 8 shows an example in which the operation key 2706 of the portable information terminal shown in FIG. 7 is operated with an 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 a thumb. Note that the operation key 2706 may be provided on a side surface of the operation panel 2702. The operation can be performed with only one index finger of the hand or the thumb.

  Note that this embodiment can be freely combined with Embodiments 1 to 5.

  In the present embodiment, a portable information terminal having a mobile phone different from that shown in the sixth embodiment will be described. FIGS. 10A and 10B are external views of the portable information terminal of this 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. In the connection portion 2903, the angle between the surface on which the display portion 2904 of the display panel 2901 is provided and the surface on which the operation key 2906 is provided on the operation panel 2902 can be arbitrarily changed.

  The display panel 2901 has a display portion 2904. 10 has a function as a telephone, the display panel 2901 has an audio output unit 2905, and audio is output from the audio output unit 2905. A liquid crystal display device having the structure of the present invention is used for the display portion 2904.

  The aspect ratio of the display unit 2904 can be arbitrarily selected such as 16: 9, 4: 3. The size of the display unit 2904 is desirably about 1 inch to 4.5 inches diagonal.

  The operation panel 2902 includes operation keys 2906, a power switch 2907, and a voice input unit 2908. In FIG. 10, the operation key 2906 and the power switch 2907 are provided separately, but the operation key 2906 may include the power switch 2907. Voice is input in the voice input unit 2908.

  Further, an image can be taken into the portable information terminal from the CCD light receiving unit 2910 as electronic information.

  Reference numeral 2911 denotes an external connection port, which can take in data from the outside. Reference numeral 2909 denotes an antenna.

  In FIG. 10, the display panel 2901 has an audio output unit 2905 and the operation panel 2902 has an audio input unit 2908, but this embodiment is not limited to this configuration. The display panel 2901 may have an audio input unit 2908 and the operation panel may have an audio output unit 2905. Further, both the audio output unit 2905 and the audio input unit 2908 may be provided on the display panel 2901, and both the audio output unit 2905 and the audio input unit 2908 may be provided on the operation panel 2902.

  In the portable information terminal shown in FIG. 10, the operation keys 2906 each have an LED, a liquid crystal, an EL, or the like. One or more characters, symbols, numbers, and the like are displayed on each operation key 2906 by the LED, liquid crystal, EL, or the like included in each operation key 2906. In the portable information terminal of this embodiment, the user can change 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 as appropriate. is there.

  FIG. 10A shows the direction of the image displayed on the display portion 2904 and the characters, numbers, and symbols displayed on the operation keys 2906 when the display panel 2901 and the operation panel 2902 are arranged in the horizontal direction. The direction of the image is the original direction when viewed from the user side.

  Although not shown, when the display panel 2901 and the operation panel 2902 are arranged in the vertical direction, the direction of the image displayed on the display unit 2904 and the characters, numbers, and characters displayed on the operation keys 2906 are displayed. The direction of the image such as a symbol may be in the original direction when viewed from the user side.

  The portable information terminal of the present invention can switch the direction of an image displayed on the display unit 2904 and the direction of an image such as letters, numbers, and symbols displayed on the operation keys 2906 in accordance with the convenience of the user. is there.

  Note that although FIG. 10 illustrates the case where 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 key 2906 are always the same, the present invention is not limited to this. . 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 may be different.

  Note that 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.

Further, 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 displayed on the surface of the connection unit 103 having the display unit 2904 and the operation. A configuration may be adopted in which switching is automatically performed according to the angle between the panel 2902 and the surface having the operation keys 2906.
These configurations are described in detail in Japanese Patent Application No. 2000-080973.

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

  Note that this embodiment can be freely combined with Embodiments 1 to 5.

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

  FIG. 16 is a top view of a pixel of a transmissive liquid crystal display device. The pixel 801 is a region including one of the source signal lines 804 and the gate signal line 803, and includes a pixel electrode 801. Although not illustrated in FIG. 16, the pixel 800 includes a pixel TFT that controls a voltage applied to the pixel electrode 801 based on a digital video signal input to the source signal line.

  If the design rule is 1 μm and the pixel pitch is about 100 ppi, the memory circuit used in the present invention can be arranged under the source signal line 804, and not only in the reflection type but also in the transmission type liquid crystal display device. Adaptable.

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

  Note that this embodiment can be freely combined with Embodiments 1 to 7.

Claims (6)

A display device, a CPU, and an external input terminal;
The display device includes a source signal line driver circuit and a plurality of pixels, and each of the plurality of pixels includes a circuit having a function of storing a video signal input to the pixels, and a pixel electrode.
When input of a signal for changing video display from the external input terminal is not performed for a certain period, the CPU determines that the display device is displaying a still image,
A portable information device, wherein when the display device displays a still image, supply of a start pulse, a clock signal, and a video data signal from the CPU to the source signal line driver circuit is stopped. A display device, a CPU, and an external input terminal;
The display device includes a source signal line driver circuit and a plurality of pixels, and each of the plurality of pixels includes a circuit having a function of storing a video signal input to the pixels, and a pixel electrode.
When input of a signal for changing video display from the external input terminal is not performed for a certain period, the CPU determines that the display device is displaying a still image,
The display device can display the still image by reading the video data signal stored in the circuit having the function of storing,
A portable information device, wherein when the display device displays a still image, supply of a start pulse, a clock signal, and a video data signal from the CPU to the source signal line driver circuit is stopped. A display device, a CPU, and an external input terminal;
The display device includes a source signal line driver circuit and a plurality of pixels, and each of the plurality of pixels includes a circuit having a function of storing a video signal input to the pixels, and a pixel electrode.
When input of a signal for changing video display from the external input terminal is not performed for a certain period, the CPU determines that the display device is displaying a still image,
When the display device displays a still image, the video display function of the CPU is stopped. A display device, a CPU, and an external input terminal;
The display device includes a source signal line driver circuit and a plurality of pixels, and each of the plurality of pixels includes a circuit having a function of storing a video signal input to the pixels, and a pixel electrode.
When input of a signal for changing video display from the external input terminal is not performed for a certain period, the CPU determines that the display device is displaying a still image,
The display device can display the still image by reading the video data signal stored in the circuit having the function of storing,
When the display device displays a still image, the video display function of the CPU is stopped. In any one of Claims 1 thru | or 4,
A portable information device comprising an EL element having the pixel electrode. In any one of Claims 1 thru | or 5,
The portable information device has a controller,
When the display device displays a still image, the portable information device stops video display functions other than the display device and the controller.

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