JP3711006B2 - Display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a display device, and more particularly to a display device suitable for use in a portable display device.
[0002]
[Prior art]
In recent years, portable display devices such as mobile TVs and mobile phones have been required as market needs. In response to such demands, research and development has been actively conducted in order to cope with the reduction in size, weight, and power consumption of display devices.
[0003]
FIG. 6 shows a circuit configuration diagram of one display pixel of a liquid crystal display device according to a conventional example. A gate signal line 51 and a drain signal line 61 intersect with each other on an insulating substrate (not shown), and a TFT 65 connected to both signal lines 51 and 61 is provided in the vicinity of the intersection. . A source 11 s of the TFT 65 is connected to a display electrode 80 that applies a voltage to the liquid crystal 21.
[0004]
Further, an auxiliary capacitor 85 for holding the voltage of the display electrode 80 for one field period is provided. One terminal 86 of the auxiliary capacitor 85 is connected to the source 11s of the TFT 65, and the other electrode 87 has each display. A common potential is applied to the pixels.
[0005]
Here, when a scanning signal is applied to the gate signal line 51, the TFT 65 is turned on, and an analog video signal is transmitted from the drain signal line 61 to the display electrode 80 and held in the auxiliary capacitor 85. A video signal voltage applied to the display electrode 80 is applied to the liquid crystal 21, and the liquid crystal 21 is aligned according to the voltage, whereby a liquid crystal display can be obtained.
[0006]
Therefore, a display can be obtained regardless of a moving image or a still image. When a still image is displayed on such a liquid crystal display device, for example, an image of a dry cell is displayed as a battery remaining amount display for driving the mobile phone on a part of the liquid crystal display unit of the mobile phone.
[0007]
However, in the liquid crystal display device having the above-described configuration, even when a still image is displayed, the TFT 65 is turned on by a scanning signal and a video signal is sent to each display pixel as in the case of displaying a moving image. There was a need to rewrite.
[0008]
For this reason, driver circuits for generating drive signals such as scanning signals and video signals, and external LSIs for generating various signals for controlling the operation timing of the driver circuits always operate, and thus always consume large power. It was. For this reason, a mobile phone or the like having only a limited power source has a drawback that the usable time is shortened.
[0009]
On the other hand, a liquid crystal display device having a static memory in each display pixel is disclosed in Japanese Patent Laid-Open No. 8-194205. Explaining a part of the publication, this liquid crystal display device, as shown in FIG. 7, retains a digital video signal in a memory in which two-stage inverters INV1 and INV2 are positively fed back, that is, a static memory. By using it as a circuit, power consumption is reduced.
[0010]
Here, according to the binary digital video signal held in the static memory, the switch element 24 controls the resistance value between the reference line Vref and the display electrode 80 and adjusts the bias state of the liquid crystal 21. . On the other hand, an AC signal Vcom is input to the common electrode. Ideally, this apparatus does not require a refresh to the memory if there is no change in the display image as in a still image.
[0011]
[Problems to be solved by the invention]
As described above, the conventional liquid crystal display device is suitable for displaying a full-color moving image corresponding to an analog video signal. On the other hand, a liquid crystal display device having a static memory for holding a digital video signal is suitable for displaying a still image with a low gradation and reducing power consumption.
[0012]
However, since both liquid crystal display devices have different video signal sources, it has not been possible to simultaneously realize full-color moving image display and still image display corresponding to low power consumption in one display device.
[0013]
Accordingly, an object of the present invention is to support two types of display, full color moving image display and low power consumption gradation display, with one display device (for example, one liquid crystal display panel). It is to provide a display device that is made possible.
[0014]
Another object of the present invention is to achieve high integration of display pixels of a display device.
[0015]
[Means for Solving the Problems]
The display device of the present invention is selected by a plurality of gate signal lines arranged in one direction on the substrate, a plurality of drain signal lines arranged in a direction crossing the gate line, and a scanning signal from the gate signal line In a display device in which display pixels to which video signals are supplied from the drain signal lines are arranged in a matrix,
A first display circuit including an auxiliary capacitor for holding an analog video signal from the drain signal line in response to a signal input from the gate signal line, and supplying the signal held in the auxiliary capacitor to a display electrode; ,
A holding circuit disposed adjacent to the first display circuit and holding a digital video signal from the drain signal line in response to a signal input from the gate signal line; and in response to a signal from the holding circuit A second display circuit including a first signal line to be supplied to the display electrode and a signal selection circuit for selecting one of the signals from the second signal line; A circuit selection circuit for selectively connecting a second display circuit to the drain signal line,
Without changing the signal of the counter electrode of the display electrode according to the circuit selection signal,
The auxiliary capacity line for biasing the auxiliary capacity electrode and the first or second signal line are shared, and the signal supplied to the auxiliary capacity line and the signal of the counter electrode are the same signal. A display device.
[0016]
According to the present invention, it is possible to select two types of display, a full-color moving image display in the analog display mode and a low power consumption digital gradation display in the digital display mode, with one display device. Since the auxiliary capacity line for biasing the auxiliary capacity electrode and the first or second signal line are shared, the auxiliary capacity line also serves as the first or second signal line, thereby reducing one signal line. be able to.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Next, a display device according to an embodiment of the present invention will be described. FIG. 1 shows a circuit configuration diagram when the display device of the present invention is applied to a liquid crystal display device.
[0018]
On the insulating substrate 10, a plurality of gate signal lines 51 connected to a gate driver 50 for supplying a scanning signal are arranged in one direction, and a plurality of drain signal lines 61 are arranged in a direction intersecting with the gate signal lines 51. Is arranged.
[0019]
Sampling transistors SP1, SP2,..., SPn are turned on to the drain signal line 61 in accordance with the timing of the sampling pulse output from the drain driver 60, and the data signal (analog video signal or digital video signal) of the data signal line 62 is turned on. ) Is supplied.
[0020]
In the liquid crystal display panel 100, a plurality of display pixels 200 that are selected by a scanning signal from the gate signal line 51 and supplied with a data signal from the drain signal line 61 are arranged in a matrix.
[0021]
Hereinafter, a detailed configuration of the display pixel 200 will be described. In the vicinity of the intersection of the gate signal line 51 and the drain signal line 61, a circuit selection circuit 40 including a P-channel TFT 41 and an N-channel type 42 is provided. Both drains of the TFTs 41 and 42 are connected to the drain signal line 61, and both gates thereof are connected to the circuit selection signal line 88. One of the TFTs 41 and 42 is turned on in response to a selection signal from the circuit selection signal line 88. Further, as will be described later, a circuit selection circuit 43 is provided in a pair with the circuit selection circuit 40.
[0022]
As a result, it is possible to select and switch between an analog video signal display (corresponding to a full-color moving image), which will be described later, and a digital video display (corresponding to low power consumption, still image). In addition, a pixel selection circuit 70 including an N-channel TFT 71 and an N-channel TFT 72 is disposed adjacent to the circuit selection circuit 40. The TFTs 71 and 72 are connected in series with the TFTs 41 and 42 of the circuit selection circuit 40, respectively, and a gate signal line 51 is connected to both gates thereof. The TFTs 71 and 72 are configured such that both are turned on simultaneously in accordance with the scanning signal from the gate signal line 51.
[0023]
In addition, an auxiliary capacitor 85 for holding an analog video signal is provided. One electrode 86 of the auxiliary capacitor 85 is connected to the source 71 s of the TFT 71. The other electrode 87 is connected to a common auxiliary capacitance line 81 and supplied with a bias voltage Vsc (for example, voltage VDD). When the gate of the TFT 71 is opened and an analog video signal is applied to the liquid crystal 21, the signal must be held for one field period. However, with only the liquid crystal 21, the voltage of the signal gradually decreases with time. If it does so, it will appear as display unevenness and a good display cannot be obtained. Therefore, an auxiliary capacitor 85 is provided to hold the voltage for one field period.
[0024]
A P-channel TFT 44 of the circuit selection circuit 43 is provided between the auxiliary capacitor 85 and the liquid crystal 21, and is configured to be turned on / off simultaneously with the TFT 41 of the circuit selection circuit 43.
[0025]
A holding circuit 110 and a signal selection circuit 120 are provided between the TFT 72 of the pixel selection circuit 70 and the display electrode 80 of the liquid crystal 21. The holding circuit 110 includes two inverter circuits that are positively fed back, and constitutes a static memory that holds a digital binary value.
[0026]
The signal selection circuit 120 is a circuit that selects a signal in accordance with a signal from the holding circuit 110, and includes two N-channel TFTs 121 and 122. Since complementary output signals from the holding circuit 110 are applied to the gates of the TFTs 121 and 122, the TFTs 121 and 122 are turned on and off in a complementary manner.
[0027]
Here, when the TFT 122 is turned on, the AC drive signal (signal B) is selected, and when the TFT 121 is turned on, the counter electrode signal VCOM (signal A) is selected, and a voltage is applied to the liquid crystal 21 via the TFT 45 of the circuit selection circuit 43. It is supplied to the display electrode 80 to be applied. When the liquid crystal display panel 100 is normally white, white display is performed when the signal A is selected, and black display is performed when the signal B is selected.
[0028]
To summarize the above configuration, a circuit (first display circuit) comprising a TFT 71 as a pixel selection element and an auxiliary capacitor 85 for holding an analog video signal, a TFT 72 as a pixel selection element, and a binary digital video signal. A holding circuit 110 for holding and a circuit (second display circuit) including a signal selection circuit 120 are provided in one display pixel 200, and circuit selection circuits 40 and 43 for selecting these two circuits are provided. Is provided.
[0029]
Next, peripheral circuits of the liquid crystal panel 200 will be described. A panel driving LSI 91 is provided on an external circuit board 90 which is a separate substrate from the insulating substrate 10 of the liquid crystal panel 200. A vertical start signal STV is input to the gate driver 50 from the panel driving LSI 91 of the external circuit board 90, and a horizontal start signal STH is input to the drain driver 60. A video signal is input to the data line 62.
[0030]
FIG. 2 is a circuit configuration diagram of a video signal switching circuit. When the switch SW1 is connected to the terminal P2 side, the n-bit digital video signal input from the input terminal Din is converted into an analog video signal by the DA converter 130 and then output to the data line 62. On the other hand, when the switch SW1 is switched to the terminal P1 side, for example, the most significant bit of the n-bit digital video signal is output to the data line 62. The switch SW1 is switched according to a mode switching signal MD for controlling switching between the analog display mode and the low power consumption compatible digital display mode.
[0031]
FIG. 3 shows another circuit configuration diagram when the display device of the present invention is applied to a liquid crystal display device. In the liquid crystal display device shown in FIG. 1, the signals A and B for monochrome display selected by the signal selection circuit 120 are supplied using signal lines 82 and 83, respectively. The auxiliary capacitance line 81 is also wired separately from these signal lines 82 and 83. For this reason, the wiring area becomes large, making it difficult to achieve high definition of the pixels.
[0032]
On the other hand, the bias voltage Vsc supplied by the auxiliary capacitance line 81 and the signal A are shared. Here, as described above, the counter electrode signal VCOM supplied to the counter electrode 32 of the liquid crystal 21 is the same as the signal A. Therefore, Vsc = signal A = counter electrode signal VCOM.
[0033]
The auxiliary capacitance line 81 is wired from the signal source to each display pixel 200, branches in each display pixel 200, extends to the position of the signal selection circuit 120, and is connected to the drain of the TFT 121 of the signal selection circuit 120. The signal line 82 for supplying the signal A in FIG. 1 is unnecessary and can be deleted. As a result, one signal line is reduced, and accordingly, the wiring area is reduced, and the pixel can be made high definition.
[0034]
Next, a method for driving the display device having the above-described configuration will be described with reference to FIGS. 2, 3, and 4. FIG. 4 is a timing chart when the liquid crystal display device is selected in the digital display mode.
(1) In the case of the analog display mode When the analog display mode is selected according to the mode switching signal MD, the analog video signal is set to be output to the data signal line 62. Further, the TFTs 41 and 44 of the circuit selection circuits 40 and 43 are turned on.
[0035]
Further, the sampling transistor SP is turned on according to the sampling signal based on the horizontal start signal STH, and the analog video signal of the data signal line 62 is supplied to the drain signal line 61.
[0036]
A scanning signal is supplied to the gate signal line 51 based on the vertical start signal STV. When the TFT 71 is turned on according to the scanning signal, the analog video signal Sig is transmitted from the drain signal line 61 to the display electrode 80 and held in the auxiliary capacitor 85. A video signal voltage applied to the display electrode 80 is applied to the liquid crystal 21, and the liquid crystal 21 is aligned according to the voltage, whereby a liquid crystal display can be obtained.
[0037]
This analog display mode is suitable for displaying a full-color moving image. However, the LSI 91 and the drivers 50 and 60 of the external circuit board 90 are constantly consuming power to drive them.
(2) When the digital display mode is selected according to the digital display mode switching signal MD, the digital video signal is set to be output to the data signal line 62. Further, the TFTs 41 and 44 of the circuit selection circuits 40 and 43 are turned off, and the TFTs 42 and 45 are turned on.
[0038]
Further, start signals STV and STH are input to the gate driver 50 and the drain driver 60 from the panel driving LSI 91 of the external circuit board 90. In response to this, sampling signals are sequentially generated, and the sampling transistors SP1, SP2,..., SPn are sequentially turned on in accordance with the respective sampling signals to sample the digital video signal Sig and supply it to each drain signal line 61.
[0039]
Here, the first row, that is, the gate signal line 51 to which the scanning signal G1 is applied will be described. First, the TFTs of the display pixels P11, P12,..., P1n connected to the gate signal line 51 by the scanning signal G1 are turned on for one horizontal scanning period.
[0040]
When attention is paid to the display pixel P11 in the first row and first column, the digital video signal S11 sampled by the sampling signal SP1 is inputted to the drain signal line 61. When the TFT 72 is turned on by the scanning signal G 1, the drain signal D 1 is input to the holding circuit 110.
[0041]
The signal held by the holding circuit 110 is input to the signal selection circuit 120, the signal selection circuit 120 selects the signal A or the signal B, the selected signal is applied to the display electrode 80, and the voltage Is applied to the liquid crystal 21. In the circuit shown in FIG. 3, a signal corresponding to the signal A is supplied from the auxiliary capacitance line 81 in common with the bias voltage Vsc of the auxiliary capacitance 85 (Vsc = signal A).
[0042]
By scanning from the gate signal line 51 to the gate signal line 51 in the last row in this way, scanning for one screen (one field period), that is, all dot scanning is completed, and one screen is displayed.
[0043]
Here, when one screen is displayed, voltage supply to the gate driver 50, the drain driver 60, and the external panel driving LSI 91 is stopped to stop driving them.
[0044]
The holding circuit 110 is always driven by supplying the voltages VDD and VSS, the counter electrode voltage is supplied to the counter electrode 32, and the signals A and B are supplied to the selection circuit 120. When the counter electrode voltage VCOM is applied to the counter electrode 32 and the liquid crystal display panel 100 is normally white (NW), a voltage having the same potential as that of the counter electrode 32 is applied to the signal A and the liquid crystal is applied to the signal B. An AC voltage (for example, 60 Hz) for driving is applied. Here, in the circuit shown in FIG. 3, the signal A is supplied from the storage capacitor line 81 (signal A = Vsc = VCOM).
[0045]
Thus, one screen can be held and displayed as a still image. In addition, no voltage is applied to the other gate driver 50, drain driver 60, and external LSI 91.
[0046]
At this time, when “H (high)” is input to the drain signal line 61 as a digital video signal to the holding circuit 110, “L” is input to the first TFT 121 in the signal selection circuit 120. Therefore, the first TFT 121 is turned off, and “H” is input to the other second TFT 122, so that the second TFT 122 is turned on.
[0047]
Then, the signal B is selected and the voltage of the signal B is applied to the liquid crystal. That is, since the alternating voltage of signal B is applied and the liquid crystal rises by an electric field, the display can be observed as a black display on the NW display panel.
[0048]
When “L” is input to the drain signal line 61 as a digital video signal to the holding circuit 110, “H” is input to the first TFT 121 in the signal selection circuit 120. Is turned on, and “L” is input to the other second TFT 122, so that the second TFT 122 is turned off.
[0049]
Then, the signal A (Vsc when supplied from the auxiliary capacitance line 81) is selected, and the voltage of the signal A is applied to the liquid crystal. That is, since the same voltage as that of the counter electrode 32 is applied, no electric field is generated and the liquid crystal does not stand up, so that the display can be observed as white display on the NW display panel.
[0050]
In this way, it is possible to display a still image by writing one screen and holding it, but in this case, the driving of the drivers 50 and 60 and the LSI 91 is stopped, so that power consumption can be reduced accordingly. it can.
[0051]
The display device of the present invention is preferably applied to a reflective liquid crystal display device among liquid crystal display devices. The device structure of this reflective liquid crystal display device will be described with reference to FIG.
[0052]
As shown in FIG. 5, on one insulating substrate 10, a gate insulating film 12 is formed on a semiconductor layer 11 made of polycrystalline silicon and formed into an island, and above the semiconductor layer 11, the gate insulating film 12 is formed. A gate electrode 13 is formed thereon.
[0053]
A source 11 s and a drain 11 d are formed in the lower semiconductor layer 11 located on both sides of the gate electrode 13. An interlayer insulating film 14 is deposited on the gate electrode 13 and the gate insulating film 12, and a contact hole 15 is formed at a position corresponding to the drain 11d and a position corresponding to the source 11s. The drain 11 d is connected to the drain electrode 16, and the source 11 s is connected to the display electrode 19 through a contact hole 18 provided in the planarization insulating film 17 provided on the interlayer insulating film 14.
[0054]
Each display electrode 19 formed on the planarization insulating film 17 is made of a reflective material such as aluminum (Al). An alignment film 20 made of polyimide or the like for aligning the liquid crystal 21 is formed on each display electrode 19 and the planarization insulating film 17.
[0055]
On the other insulating substrate 30, a color filter 31 exhibiting each color of red (R), green (G), and blue (B), a counter electrode 32 made of a transparent conductive film such as ITO (Indium Tin Oxide), And the alignment film 33 which orientates the liquid crystal 21 is formed in order. When color display is not used, the color filter 31 is not necessary.
[0056]
The periphery of the pair of insulating substrates 10 and 30 thus formed is adhered with an adhesive sealing material, and the liquid crystal 21 is filled in the gap formed thereby, thereby completing the reflective liquid crystal display device.
[0057]
As indicated by the dotted arrows in the figure, the external light incident from the viewer 1 side enters from the counter electrode substrate 30 in order, is reflected by the display electrode 19, is emitted to the viewer 1 side, and the display is viewed by the viewer 1. Can be observed.
[0058]
Thus, the reflective liquid crystal display device is a method of observing the display by reflecting external light, and unlike the transmissive liquid crystal display device, it is not necessary to use a so-called backlight on the side opposite to the viewer side. Does not require power to turn on its backlight. Therefore, the display device of the present invention is preferably a reflective liquid crystal display device that does not require a backlight and is suitable for power saving.
[0059]
In the above-described embodiment, the case where the counter electrode voltage and the voltages of the signals A and B are applied during the entire dot scan period of one screen has been described, but the present invention is not limited thereto. It is not necessary to apply these voltages during this period. However, in order to reduce power consumption, it is preferable not to apply.
[0060]
In the above-described embodiment, the case where a 1-bit digital data signal is input in the digital display mode has been described. However, the present invention is not limited thereto, and even in the case of a multi-bit digital data signal. It is possible to apply. By doing so, multi-gradation display can be performed. At that time, it is necessary to set the number of holding circuits and signal selection circuits according to the number of input bits.
[0061]
In the above-described embodiment, the case where a still image is displayed on a part of a liquid crystal display panel has been described. However, the present application is not limited thereto, and a still image can be displayed on all display pixels. Thus, the present invention has a characteristic effect of the present invention.
[0062]
In the above-described embodiment, the case of the reflective liquid crystal display device has been described. However, by disposing a transparent electrode in a region excluding the TFT, the holding circuit, the signal selection circuit, and the signal wiring in one pixel, the transmissive liquid crystal It can also be used for a display device. Also, when used in a transmissive liquid crystal display device, after displaying one screen, the supply of voltage to the gate driver 50, the drain driver 60, and the external panel driving LSI 91 is stopped, thereby consuming the corresponding amount. Electric power can be reduced.
[0063]
【The invention's effect】
According to the display device of the present invention, it is possible to select two types of display, a full color moving image display in the analog display mode and a low power consumption digital gradation display in the digital display mode, with one display device. Become.
[0064]
In addition, since the auxiliary capacitance line for biasing one electrode of the auxiliary capacitance and the first or second signal line are shared, one signal line can be reduced and high definition of the pixel can be realized. Can do.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram of a liquid crystal display device according to an embodiment of the present invention.
FIG. 2 is a circuit configuration diagram of a video signal switching circuit according to an embodiment of the present invention.
FIG. 3 is another circuit configuration diagram of the liquid crystal display device according to the embodiment of the present invention.
FIG. 4 is a timing chart of the liquid crystal display device according to the embodiment of the invention.
FIG. 5 is a cross-sectional view of a reflective liquid crystal display device.
FIG. 6 is a circuit configuration diagram of a liquid crystal display device according to a conventional example.
FIG. 7 is another circuit configuration diagram of a liquid crystal display device according to a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Insulating substrate 13 Gate 21 Liquid crystal 40 Circuit selection circuit 43 Circuit selection circuit 50 Gate driver 51 Gate signal line 60 Drain driver 61 Drain signal line 70 Pixel selection circuit 85 Auxiliary capacity 110 Holding circuit 120 Signal selection circuit

Claims (1)

A plurality of gate signal lines arranged in one direction on the substrate, a plurality of drain signal lines arranged in a direction crossing the gate signal line, and the drain selected by the scanning signal from the gate signal line In a display device in which display pixels to which video signals are supplied from signal lines are arranged in a matrix,
A first display circuit comprising an auxiliary capacitor for holding an analog video signal from the drain signal line in response to a signal input from the gate signal line, and supplying a signal held in the auxiliary capacitor to a display electrode;
A holding circuit disposed adjacent to the first display circuit and holding a digital video signal from the drain signal line in response to a signal input from the gate signal line; and in response to a signal from the holding circuit A second display circuit comprising a first signal line supplied to the display electrode and a signal selection circuit for selecting one of the signals from the second signal line; and the first display circuit according to a circuit selection signal And a circuit selection circuit for selectively connecting a second display circuit to the drain signal line,
Without changing the signal of the counter electrode of the display electrode according to the circuit selection signal,
The auxiliary capacity line for biasing the auxiliary capacity electrode and the first or second signal line are shared, and the signal supplied to the auxiliary capacity line and the signal of the counter electrode are the same signal. A display device.

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