Patent Grant
7633592
This application is based on Japanese Patent Application No. 2005-201182, the content of which is incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a liquid crystal display device and an electronic device including the display device, specifically to a liquid crystal display device using an active matrix substrate.
2. Description of the Related Art
A liquid crystal display device with an active matrix circuit using active devices such as TFTs (Thin Film Transistors) has come into widespread use including a laptop PC and a monitor in recent years.
In a liquid crystal display device using a conventional nematic liquid crystal material, a display status of each pixel is controlled by an electric potential difference between a pixel electrode switched by the active device and a common electrode. When a large electric potential difference is applied between the pixel electrode and the common electrode, that is, when black is displayed in a normally white mode or when white is displayed in a normally black mode, a maximum electric potential difference between the common electrode and the pixel electrode is usually three to five volts, although it varies depending on the liquid crystal material used, a mode of the liquid crystal and a gap of the liquid crystal. In order to secure reliability of the liquid crystal device, the liquid crystal display device requires inverting a polarity of voltage applied to the liquid crystal at a certain interval, or an alternating current drive. Assuming that the electric potential of the common electrode is fixed, the electric potential amplitude of a signal written into the pixel electrode, that is, a video signal inputted to a data line of the active matrix circuit, is six to ten volts.
When the video signal inputted to the data line is written-in by an external data driver IC, however, an expensive IC manufactured, not only by a conventional CMOS process but by a high withstand voltage process, is required in order to output the electric potential amplitude higher that five volts, leading to an increased cost and increase power consumption. To solve the problem described above, a drive method to reduce by half the amplitude of the input signal to the data line by using a common inversion drive in which the polarity of the common electrode is alternated is proposed in Japanese Patent Application Publication No. S62-49399, for example.
When the common inversion drive proposed above is applied to a large and high resolution display panel, however, capacitance of the common electrode is increased to increase a relaxation time and the maximum instantaneous current at a common electric potential inversion timing.
This invention is directed to solving the problems addressed above, and offers a liquid crystal display device and an electronic having the display device, which are small in dimensions of periphery of the panel and low in power consumption.
This invention provides a liquid crystal display device having a plurality of scan lines, a plurality of data lines disposed to intersect the scan lines, a plurality of pixel switching devices disposed corresponding to intersections of the data lines and the scan lines, a plurality of pixel electrodes disposed corresponding to the pixel switching devices, a common electrode facing to the pixel electrodes to form capacitors, a common power supply circuit connected with the common electrode and outputting a square wave signal alternating between a higher electric potential and a lower electric potential at regular intervals and a first reference electric potential power supply circuit that outputs a first reference electric potential of a constant electric potential to the scan lines at a common electric potential inversion timing that is a timing of alternation of the square wave signal, wherein the first reference electric potential power supply circuit is connected to the common power supply circuit through a low impedance and an impedance RA between the common power supply circuit and the common electrode is approximately the same as an impedance RB between the first reference electric potential power supply circuit and the scan lines.
With a structure described above, a relaxation time at the common electric potential inversion timing can be suppressed and a period from the common electric potential inversion timing to a timing to write a selection electric potential into the scan line and a period to select the scan line can be secured. As a result, it is made possible to apply the common inversion drive to a panel that has been difficult to apply the common inversion drive and to manufacture the panel with a high yield. It is also made possible to realize a low cost, low power consumption liquid crystal display device, using a less expensive low withstand voltage IC as an external driver IC without reducing yields.
This invention also provides the liquid crystal display device further including a first wiring that electrically connects the first reference electric potential power supply circuit with the scan lines and a second wiring that electrically connects the common power supply circuit with the common electrode, wherein a width of the first wiring is approximately equal to a width of the second wiring.
With a structure described above, the relaxation time at the common electric potential inversion timing can be optimized by specifying the widths of the first and second wirings.
And in the liquid crystal display device of this invention, among widths of the wirings connecting signal sources and the power supplies to the drive circuits, the width of the first wiring and the width of the second wiring are greater than widths of the other wirings.
With a structure described above, the relaxation time at the common electric potential inversion timing can be optimized making resistances of the first and second wirings smaller than resistances of the other wirings.
This invention also provides the liquid crystal display device further including a plurality of mounting terminals formed on a single substrate together with the plurality of scan lines, the plurality of data lines and the plurality of pixel switching devices, the plurality of mounting terminals including a first mounting terminal connected with the first reference electric potential power supply circuit and a second mounting terminal connected with the common power supply circuit, wherein the first mounting terminal is approximately equal to the second mounting terminal in the number of constituting unit mounting terminals or in an area of the terminal.
With a structure described above, a liquid crystal display device with a large display area, a small panel periphery dimensions and small current consumption can be manufactured, since the relaxation time at the common electric potential inversion timing can be optimized by specifying the areas of the first and second mounting terminals while optimizing outer dimensions of the panel. And the cost can be reduced by using the low withstand voltage IC.
And in the liquid crystal display device of this invention, the first and second mounting terminals are larger in the number of unit mounting terminals or larger in the area of the terminal compared with the other mounting terminals for other signals and a power supply.
With a structure described above, the relaxation time at the common electric potential inversion timing can be optimized by making resistances of the first and second mounting terminals smaller than resistances of the other mounting terminals.
This invention also provides the liquid crystal display device further including a second reference electric potential power supply circuit that is connected with the data lines through a low impedance and outputs a second reference electric potential of a constant electric potential at the common electric potential inversion timing, that is the timing of inversion of the output of the common power supply circuit.
With a structure described above, a write-in time can be reduced by performing a precharge operation for a period encompassing the common electric potential inversion timing, to realize a larger display area and lower power consumption.
This invention also provides the liquid crystal display device further including a third wiring that electrically connects the second reference electric potential power supply circuit with the plurality of data lines, wherein a sum of the width of the first wiring and a width of the third wiring is approximately equal to the width of the second wiring.
With a structure described above, the relaxation time at the common electric potential inversion timing can be optimized in the liquid crystal display device having a precharge function by considering the width of the third wiring that electrically connects the data lines.
In the liquid crystal display device of this invention, among the widths of wirings connecting the signal sources and the power supplies to the drive circuits, the widths of the first, second and third wirings are greater than widths of the other wirings.
With a structure described above, the relaxation time at the common electric potential inversion timing can be optimized by making the resistances of the first, second and third wirings smaller than the resistances of the other wirings.
This invention also provides the liquid crystal display device further including a third mounting terminal that is a part of the plurality of mounting terminals and connected with the second reference electric potential power supply circuit, wherein a sum of the number of unit mounting terminals of the first mounting terminal and the number of unit mounting terminals of the third mounting terminal is approximately equal to the number of unit mounting terminals of the second mounting terminal or a sum of the area of the first mounting terminal and an area of the third mounting terminal is approximately equal to the area of the second mounting terminal.
With a structure described above, the relaxation time at the common electric potential inversion timing can be optimized in the liquid crystal display device having the precharge function by considering the area of the third mounting terminal that electrically connects the data lines.
And in the liquid crystal display device of this invention, the first, second and third mounting terminals are larger in the number of unit mounting terminals or larger in the area compared with the other mounting terminals for other signals and the power supply.
With a structure described above, a liquid crystal display device with a large display area, a small panel periphery dimensions and small current consumption can be manufactured, since the relaxation time at the common electric potential inversion timing can be optimized by reducing the resistance of the other mounting terminals while optimizing the outer dimensions of the panel, even when the precharge operation is performed for the period encompassing the common electric potential inversion timing.
This invention also provides a liquid crystal display device including a plurality of scan lines, a plurality of data lines disposed to intersect the scan lines, a plurality of pixel switching devices disposed corresponding to intersections of the data lines and the scan lines, a plurality of pixel electrodes disposed corresponding to the pixel switching devices, a common electrode facing to the pixel electrodes to form capacitors, a common power supply circuit connected with the common electrode and outputting a square wave signal alternating between a higher electric potential and a lower electric potential at regular intervals, a first reference electric potential power supply circuit that provides the scan lines with a non-select electric potential, a common electric potential wiring that electrically connects a common electric potential terminal receiving the square wave signal from the common power supply circuit with the common electrode, and a power supply wiring that connects a power supply terminal receiving the non-select electric potential from the first reference electric potential power supply circuit with a scan line drive circuit that drives the scan lines, wherein impedance of the common electric potential wiring is approximately equal to an impedance of the power supply wiring.
With a structure described above, the relaxation time at the common electric potential inversion timing can be suppressed and the period from the common electric potential inversion timing to the timing to write the selection electric potential into the scan line and the period to select the scan line can be secured. As a result, it is made possible to apply the common inversion drive to a panel that has been difficult to apply the common inversion drive and to manufacture the panel with a high yield. It is also made possible to realize a low cost, low power consumption liquid crystal display device, using a less expensive low withstand voltage IC as an external driver IC.
This invention offers an electronic device provided with the liquid crystal display device described above.
With a structure described above, a low cost electronic device with high picture quality display which operates for many hours with a battery is made available, since the less expensive low withstand voltage IC can be used as the external driver IC and the low power consumption liquid crystal display device with less visible flicker can be used as a display. To be more specific, the electronic device means a monitor, a TV, a note PC, a PDA (Personal Digital Assistant), a digital still camera, a camcorder, a mobile telephone, a mobile photo viewer, a mobile video player, a mobile DVD player, a mobile audio player and the like.
A liquid crystal display device according to embodiments of this invention will be explained hereafter referring to the drawings.
An upper polarizing plate 24 is disposed on a outer surface of the counter substrate 12 and a lower polarizing plate 25 is disposed on a outer surface of the active matrix substrate 11 so that directions of polarization of the two polarizing plates are orthogonal to each other (cross-Nicol arrangement). A back light unit 26 that makes a surface light source is disposed under the lower polarizing plate 25. The back light unit 26 may be a cold cathode tube or an LED (Light-Emitting Diode) attached to an optical waveguide plate or a scattering plate, or a unit that is made of electroluminescent device and emits light from its whole surface. The back light unit 26 is connected to a body of an electronic device through a connector 26a and is provided with a power supply and a control signal. Although not shown in the figure, a hull may be attached to cover the liquid crystal display device 10, a protection glass or acryl plate may be attached over the upper polarizing plate 24, or an optical compensation film may be stuck to it in order to improve a viewing angle, if necessary.
The active matrix substrate 11 has an extended portion 27 that sticks out of the counter substrate 12. The extended portion 27 is provided with a plurality of signal input terminals 53 (not shown). An FPC (Flexible Printed Circuit Board) 28 and an external driver IC 29 are mounted on the extended portion 27 and are electrically connected with the signal input terminals 53. Although the external driver IC 29 is formed of two ICs in
Next, a structure of the active matrix substrate 11 is described referring to
The scan lines 31 are connected to a scan line drive circuit 41. The scan line drive circuit 41 is connected with a power supply terminal 51 through a power supply wiring 52, and is also connected with the signal input terminals 53 through a plurality of signal wirings 57. The scan line drive circuit 41 is provided from the power supply terminal 51 with a DC power supply electric potential VBB (−4V) that renders the scan lines 31 in holding state (non-selected state) and from the signal input terminals 53 with various necessary signals and a signal to give the power supply electric potential. A data line drive circuit 42 is connected to the data lines 32. The data line drive circuit 42 is connected to the signal input terminals 53 through the signal wirings 57 and is provided with various necessary signals and the signal to give the power supply electric potential.
The capacitor lines 33 are connected with each other and connected to a common electric potential input terminal 54 through a common electric potential wiring 55, and are provided with a common electric potential signal VCOM (an inverting signal alternating between −4.5V and −0.5V). The counter electrode 30 on the counter substrate 12 is connected with the vertical conduction portion 56 that is disposed at each of four corners of the active matrix substrate 11 and is similarly connected to the common electric potential input terminal 54 through the common electric potential wiring 55.
Next, a structure of a pixel circuit is described referring to
Next, a structure of the scan line drive circuit 41 is described referring to
The scan line drive circuit 41 is composed of clock control circuits (CCC) 72, clock generation circuits (CGC) 73, latch circuits (LAT) 74, bidirectional transfer circuits (DIR) 75, NAND circuits 76, level shift circuits (L/S) 81 and output circuits 82. The clock control circuits 72, the clock generation circuits 73, the latch circuit 74, the bidirectional transfer circuits 75 and the NAND circuits 76 are provided with a power supply electric potential VD (5V) and a power supply electric potential VS (0V) from the external driver IC 29 through the signal input terminals 53 and the signal wirings 57, although not shown in the figure. Similarly, the level shift circuits 81 are provided with the power supply electric potential VS (0V), a power supply electric potential VHH (9V) and a power supply electric potential VBB (−4V), while the output circuits 82 are provided with the power supply electric potential VHH (9V) and the power supply electric potential VBB (−4V).
In the clock control circuit 72, as shown in
Next, in the clock generation circuit 73, the clock signal VCLK, that is a unipolar clock signal outputted from the terminal OUT of the clock control circuit 72, is inputted to a terminal IN, as shown in
The latch circuit 74 latches or sequentially transfers a start pulse signal VSP inputted to a terminal IN from the signal input terminal 53 through the bidirectional transfer circuit 75 with the clock signals CL and CX generated from the clock signal VCLK in the clock generation circuit 73. That is, the latch circuit 74 transfers the start pulse signal VSP when the clock signal CL is high and the reverse clock signal CX is low, and latches it when the clock signal CL is low and the reverse clock signal CX is high. And the latch circuit 74 is reset and forced to output a low level when an initialization signal INIT is high.
The bidirectional transfer circuits 75 perform a forward transfer that data is transferred from the first scan line 31 toward the m-th scan line 31 when a transfer direction control signal VDIR is high and a reverse transfer direction control signal VDIRX is low, and perform a reverse transfer that the data is transferred from the m-th scan line toward the first scan line when the transfer direction control signal VDIR is low and the reverse transfer direction control signal VDIRX is high, as shown in
An output signal OUT of the latch circuit 74, another output signal OUT of a preceding or following stage of the latch circuit and an enable signal VEMB inputted from the signal input terminal 53 are inputted to the NAND circuit 76. The NAND circuit 76 outputs a result of NAND of the inputted signals. To be more specific, only a selected stage of NAND circuit 76 outputs a low (VS) level at timing when the output signal OUT from the latch circuit 74 is inputted to the NAND circuit 76 and the enable signal VEMB is at a high (VD) level, while the other stages of NAND circuits 76 output the high (VD) level. The signal ranging between VD and VS is converted to a signal ranging between VHH and VBB by the level shift circuit 81 and inputted to gate electrodes of a P-channel type transistor 83 and an N-channel type transistor 84 in the output circuit 82.
Next, a structure of the data line drive circuit 42 is described referring to
With the structure as shown in
Next, operation of the common electric potential signal VCOM and the scan lines 31 are described hereafter, referring to
t1+t2+t3=34.7 microseconds
How to decide t1, t2 and t3 will be described later.
Next, a capacitance of the common electric potential input terminal 54 at the common electric potential inversion timing is described, referring to
A VCOM power supply circuit 111, a VBB power supply circuit 112, a plurality of video signal circuits 113 and a VHH power supply circuit 114 are integrated in the external driver IC 29. The VCOM power supply circuit 111 is an AC power supply outputting an electric potential shown as the waveform 101 in
The VBB power supply circuit 112 is a DC power supply outputting the power supply electric potential VBB and having an IC internal impedance Ric2, and is connected to the power supply terminal 51. The VBB power supply circuit 112 is connected to the power supply wiring 52 on the active matrix substrate 11 through a mounting resistance Rin2 and is further connected to the scan line drive circuit 41 through the power supply wiring 52. That is, the power supply wiring 52 connects the power supply terminal 51 and the scan line drive circuit 41. The power supply wiring 52 has a wiring resistance Rl2. All the scan lines 31 are connected to the power supply electric potential VBB at the common electric potential inversion timing through the N-channel type transistors 84, each having an output impedance of Rn×m. Estimating that a VBB line impedance for each scan line in the scan line drive circuit is Rg×m, the VBB line impedance in the lumped constant model is represented by a resistance Rg/2. The scan line 31 having a resistance Rg is connected to the gate electrode of each pixel switching device 34.
The video signal circuits 113 output the 320 video signals VIDEO1-VIDEO320, having an IC internal impedance Ric3, and are connected to the signal input terminals 53. Although he video signals VIDEO1-VIDEO320 from the video signal circuits 113 are inputted to the data line drive circuit 42 through a mounting resistance Rin3, all the data lines 32 are in high impedance state at the common electric potential inversion timing.
The VHH power supply circuit 114 is a DC power supply outputting the power supply electric potential VHH (9V) as a selection electric potential, having an IC internal impedance Ric4, and is connected to the signal input terminal 53. The VHH power supply circuit 114 is further connected to a power supply wiring on the active matrix substrate 11 through a mounting resistance Rin4. Although the electric potential VHH is inputted to the scan line drive circuit 41 through a power supply wiring, all the scan lines 31 are in high impedance state at the common electric potential inversion timing.
For all the pixels combined, there are a capacitance Cgd between the scan lines 31 (electric potential of the scan lines) and the pixel electrodes 35 (electric potential at the pixel electrodes), a capacitance Cgs between the scan lines 31 (electric potential of the scan lines) and the data lines 32 (electric potential of the data lines), a capacitance Clc between the pixel electrodes 35 (electric potential at the pixel electrodes) and the counter electrode 30 (electric potential at the counter electrode), a capacitance Cs between the pixel electrodes 35 (electric potential at the pixel electrodes) and the capacitor lines 33 (electric potential of the capacitor lines) and a capacitance Ccs between the capacitor lines 33 (electric potential of the capacitor lines) and the data lines 32 (electric potential of the data lines).
Since all the scan lines 31 are connected to the power supply electric potential VBB (−4V), all the pixel switching devices 34 are in the high impedance state.
From results of calculations of electric fields, the capacitances in this embodiment are, Cs=600 nF, Clc=100 nF, Cgd=1 nF, Ccs=5 nF and Cgs=2 nF. Further approximation using these capacitances and omission of devices in the high impedance state simplifies the circuit in
A relaxation time τcom at the VCOM inversion timing is represented by the following equation:
τcom=(Cgd+1/(1/Ccs+1/Cgs))×(Ric1+Ric2+Rin1+Rin2+Rl1+Rl2+Rn+Rg/2+Rc/2)
Values of Cgd, Ccs and Cgs are determined almost by the number of pixels, an aperture ratio of the pixels, design rules, device structures of the TFTs and so on, with little room to be reduced by the design without tradeoff against performances, and increase roughly proportional to the number of pixels and a display area.
If VHH is written into the scan line 31 before the common electric potential completes the inversion, however, load capacitances increase because the pixel switching devices 34 connected to the scan line 31 become of low impedance. Therefore, the period t1 shown in FIG. 7 is required to be equal to or longer than a length of time which the common electric potential takes to complete 95% of the inversion, or satisfy the equation 3×τcom≦t1, so that VHH is not written into the scan line 31 before the common electric potential completes the inversion. Thus the period t1 increases as the number of pixels and the display area increase.
On the other hand, while a relaxation time τcom at writing of VBB into the scan line 31 is represented by an equation τgate=(Rg/2+Rn+Rl2)×(capacitance of the scan line 31), the period t3 is required to satisfy the equation 3×τgate≦t3. Thus the period t3 also increases as the number of pixels and the display area increase.
As a result, the period t2 decreases as the number of pixels and the display area increase, eventually leading to a lack of write-in time into the data line 32 and the pixel electrode 35, reducing a manufacturing yield because of thin margin in the manufacturing process. While the period t3 does not depend on the driving method, the period t1 can be reduced to almost zero by using a fixed common drive in which the common electric potential VCOM is fixed to a DC electric potential. That means the common inversion drive gets more restriction than the fixed common drive as the display becomes higher in the resolution and larger in the area. To reduce the restriction, the relaxation time τcom at the common electric potential inversion timing needs to be reduced.
Optimization has to be made for that purpose so as to minimize the value of (Ric1+Ric2+Rin1+Rin2+Rl1+Rl2+Rn+Rg/2+Rc/2). Here, Rc<Rg<Rn<<Rl1, Rl2, Rin1, Rin2. The IC internal impedances Ric1 and Ric2 are fixed values because they are determined by the performance of the IC. To reduce the output impedance Rn of the N-channel type transistors 84 in the output circuit 82, size of the N-channel type transistors 84 is increased to cause a tradeoff against the outer dimensions of the liquid crystal display device 10. Therefore, (Rl1+Rl2+Rin1+Rin2) needs to be reduced in designing as much as possible. An impedance RA between the VCOM power supply circuit 111 and the counter electrode (common electrode) 30 is represented by an equation:
RA=Rin1 (the mounting resistance of the common electric potential input terminal 54)+Rl1 (the wiring resistance of the common electric potential wiring 55),
while an impedance RB between the VBB power supply circuit 112 and the scan line 31 is represented by an equation:
RB=Rin2 (the mounting resistance of the power supply terminal 51 of the power supply electric potential VBB)+Rl2 (the wiring resistance of the power supply wiring 52).
The wiring resistance Rl1 of the common electric potential wiring 55 is inversely proportional to a width W1 of the common electric potential wiring 55, while the wiring resistance Rl2 of the power supply wiring 52 is inversely proportional to a width W2 of the power supply wiring 52. However, a size of the active matrix substrate 11 is determined by the outer dimensions required to the liquid crystal display device 10. When a sum of the signal wirings 57 is denoted by w3, (w1+w2+w3) has to be a predetermined value. Since the minimum line width is determined by requirements of the circuit design or the manufacturing technology, w3 may be set to the minimum value within the requirements. If the common electric potential wiring 55 and the power supply wiring 52 are approximately equal in length to each other, it is necessary to minimize (Rl1+Rl2) that is proportional to (1/W1+1/W2) while satisfying an equation w1+w2=w0 (constant). The solution is w1=w2=½×w0. Since the external dimensions require w0=600 μm in this embodiment, assuming the width of the signal wiring 57 be the practical minimum of 10 μm, the width of the common electric potential wiring is made 300 μm, the width of the power supply wiring 52 is made 300 μm and the width of each of the other signal wirings is made 10 μm. At that time, Rl1=Rl2=30Ω.
As described above, the common inversion relaxation time τcom can be minimized by minimizing the widths of the other signal wirings 57 and setting the width of the common electric potential wiring 55 and the width of the power supply wiring 52 approximately the same maximum width. The width of the common electric potential wiring 55 and the width of the power supply wiring 52 are made precisely equal to each other in this embodiment. Although the widths may differ from each other slightly when the length of the common electric potential wiring 55 is different from the length of the power supply wiring 52 or when there is a restriction in the layout, it is preferable that the wiring resistance Rl1 of the common electric potential wiring 55 and the wiring resistance Rl2 of the power supply wiring 52 are approximately equal to each other. And although the signal wirings 57 may vary in width among themselves in response to a function of each signal, it is preferable that they are smaller in width than any one of the common electric potential wiring 55 and the power supply wiring 52. Here, the signal wirings 57 mean wirings providing the scan line drive circuit 41 with the clock signal VCLK, the start pulse signal VSP, the enable signal VENB and the electric potential VHH as the selection electric potential and the wirings providing the data line drive circuit 42 with the video signals VIDEO1-VIDEO320.
The mounting resistance Rin1 of the common electric potential input terminal 54 is approximately inversely proportional to a total area S1 of the common electric potential input terminal 54, while the mounting resistance Rin2 of the power supply terminal 51 of power supply electric potential VBB is approximately inversely proportional to a total area S2 of the power supply terminal 51. However, a sum of the total areas of the power supply terminal 51, the signal input terminals 53 and the common electric potential input terminal 54 needs to be suppressed to a certain value or less due to restrictions by the size of the external IC to be mounted and mounting process. Also a minimum area S3 of the signal input terminal 53 is limited to a certain value because of the mounting resistance and accuracy of the mounting. That is, (S1+S2) also needs to be suppressed to a certain value. The requirement is to minimize (Rin1+Rin2) that is proportional to (1/S1+1/S2), while satisfying S1+S2=S0 (constant). So, the best solution to the requirement is S1=S2=½×S0. Since S0=15000 square micrometers in this embodiment due to various restrictions, it is set that S1=S2=7500 square micrometers.
Next, an arrangement of the mounting terminals is described referring to
Although the impedance RA between the VCOM power supply circuit 111 and the counter electrode 30 is made exactly equal to the impedance RB between the VBB power supply circuit 112 and the scan line 31 in the embodiment, a ratio of RA to RB varies in a range between 1:2 and 2:1 due to manufacturing variations in reality. However, it is expected that the effect of the invention is obtained in a range of the ratio of RA to RB between 1:6 and 6:1.
Although each of the plurality of signal input terminals 53 is assumed to have the same mounting terminal area, each of them may have a different terminal area depending on its function. Even in that case, however, it is preferable that the area of the common electric potential input terminal 54 and the area of the power supply terminal 51 are larger than any of the other signal input terminals 53. When the number of the unit mounting terminals assignable to the power supply terminal 51 and the common electric potential input terminal 54 is odd number, either of them may be assigned one more unit mounting terminal than the other.
In this embodiment, since Ric1=35Ω, Ric2=20Ω, Rn=3Ω, Rg=10Ω and Rc=2Ω, the common inversion relaxation time τcom=140Ω×2.4 nF=340 nanoseconds. Setting the period t1, that is the period between the common electric potential inversion timing and the timing when VHH is written into the scan lines 31, to be 1 microsecond, an enough write-in time, that is the scan line selection period t2=32.7 microseconds, can be secured. As a result, it is made possible to apply the common inversion drive to a four inch diagonal panel with VGA resolution that has been difficult to apply the common inversion drive and to manufacture the panel with a high yield. Therefore, it is made possible to realize a low cost, low power consumption liquid crystal display device using a less expensive low withstand voltage IC as an external driver IC without reducing yields.
Next, a liquid crystal display device according to a second embodiment of this invention is described.
On the active matrix substrate 11 according to the second embodiment, m scan lines 31 and n data lines 32 are formed to intersect with each other, and m capacitor lines 33 are disposed parallel to the scan lines 31 so that each of the capacitor lines 33 is paired with each of the scan lines 31.
The scan lines 31 are connected to a scan line drive circuit 41. A power supply terminal 51 is connected to the scan line drive circuit 41 through a power supply wiring 52 as well as a plurality of signal input terminals 53 being connected through a plurality of signal wirings 57. The scan line drive circuit 41 is provided from the power supply terminal 51 with a DC power supply electric potential VBB (−4V) that renders the scan lines 31 in holding state (non-selected state) and from the signal input terminals 53 with various necessary signals and a signal to give the power supply electric potential. One end of each of the data lines 32 is connected with the data line drive circuit 42 while the other end of it is connected with a data line precharge circuit 43. The data line drive circuit 42 is connected to the plurality of signal input terminals 53 through the signal wirings 57 and is provided with various necessary signals and a signal to give the power supply electric potential. The data line precharge circuit 43 is connected with a timing signal terminal 151 through a timing signal wiring 152 as well as connected with a precharge electric potential terminal 153 through a precharge electric potential wiring 154.
The capacitor lines 33 are connected with each other and connected to a common electric potential input terminal 54 through a common electric potential wiring 55, and are provided with a common electric potential signal VCOM that alternates between −4.5V and −0.5V. The counter electrode on the counter substrate is connected with the vertical conduction portion 56 that is disposed at each of four corners of the active matrix substrate 11 and is similarly connected to the common electric potential input terminal 54 through the common electric potential wiring 55.
The timing signal PRC is at a high level (9V) for a period of 5 microseconds encompassing the timing when VCOM inverts and is at a low level (−4V) for the other period, as shown in
Descriptions of structures of pixels disposed at intersections of the scan lines 31 and the data lines 32, the scan line drive circuit 41 and the data line drive circuit 42 are omitted because they are same as those in the first embodiment. The second embodiment is largely different from the first embodiment in that the data lines 32 are short-circuited to the precharge electric potential PRV at the VCOM inversion timing in the second embodiment.
Capacitances in the second embodiment are the capacitance Cs=600 nF between the pixel electrodes 35 and the capacitor lines 33, the capacitance Clc=100 nF between the pixel electrodes 35 and the counter electrode 30, the capacitance Cgd=1 nF between the scan lines 31 and the pixel electrodes 35, the capacitance Ccs=5 nF between the capacitor lines 33 and the data lines 32 and the capacitance Cgs=2 nF between the scan lines 31 and the data lines 32. Further approximation based on the above leads to a simplified model shown in
Rl1 (the wiring resistance of the common electric potential wiring 55)=(Ccs+Cgd)/Cgd×Rl2 (the wiring resistance of the power supply wiring 52).
Rl4 (a wiring resistance of the precharge electric potential wiring 154)=(Ccs+Cgd)/Ccs×Rl2 (the wiring resistance of the power supply wiring 52).
Rin1 (the mounting resistance of the common electric potential input terminal 54)=(Ccs+Cgd)/Cgd×Rin2 (the mounting resistance of the power supply terminal 51 of the power supply electric potential VBB).
Rin4 (a mounting resistance of the precharge electric potential terminal 153)=(Ccs+Cgd)/Ccs×Rin2 (the mounting resistance of the power supply terminal 51 of the power supply electric potential VBB).
That is, it is preferable that 1/Rl1+1/Rl4=1/Rl2 and 1/Rin1+1/Rin4=1/Rin2, a sum of the width of the power supply wiring 52 and a width of the precharge electric potential wiring 154 is approximately equal to a width of the common electric potential wiring 55 and a sum of an area of the power supply terminal 51 and an area of the precharge electric potential terminal 153 is approximately equal to an area of the common electric potential input terminal 54.
Based on the above, the width of the common electric potential wiring 55 is made 300 μm, the width of the precharge electric potential wiring 154 is made 250 μm and the width of the power supply wiring 52 is made 50 μm. The width of each of the signal wirings 57 and the timing signal wirings 152 is 10 μm that is a minimum width according to the design rules. At that time, Rl2=30Ω, Rl1=180Ω and Rl4=360Ω. The common electric potential input terminal 54 uses five unit mounting terminals, each measuring 30 μm×50 μm, the precharge electric potential terminal 153 similarly uses four unit mounting terminals, each measuring 30 μm×50 μm, while the power supply terminal 51, each of the signal input terminals 53 and each of the timing signal terminals 151 use one unit mounting terminal measuring 30 μm×50 μm, as shown in
With the settings described above, the common inversion relaxation time τcom becomes 1.3 microseconds. Enough relaxation time τcom and charging time are obtained by setting t1 (the period between the common electric potential inversion timing and the timing when VHH is written into the scan lines 31)=4 microseconds and t2 (the scan line selection period)=29.7 microseconds.
An electronic device according to a third embodiment of this invention is described hereafter. Note that the third embodiment shows an example this invention, which is not limited to the third embodiment.
The display information processing circuit 780 re-writes video data stored in a RAM (Random Access Memory) at appropriate timings and provides the liquid crystal display device 10 with the video data together with timing signals, based on commands from the central processing circuit 781. The central processing circuit 781 performs various processing based on inputs from the external I/F circuit 782 and outputs the commands to the display information processing circuit 780 and the external I/F circuit 782 based on results of the processing. The external I/F circuit 782 controls the input/output devices 783 based on the commands from the central processing circuit 781 as well as sending information from the input/output devices 783 to the central processing circuit 781. The input/output devices 783 refer to a switch, a keyboard, a hard disk drive, a flash memory unit and the like. The power supply circuit 784 provides the above-mentioned components with a predetermined power supply voltage.
The electronic device refers to a monitor, a TV, a note PC, a PDA (Personal Digital Assistant), a digital still camera, a camcorder, a mobile telephone, a photo viewer, a video player, a DVD player, an audio player or the like.
This invention is not limited to the embodiments described above and may be applied to a liquid crystal display device not only of a TN (twisted nematic) mode but also of a VA (Vertical Alignment) mode that uses a liquid crystal having a negative dielectric constant anisotropy or of an IPS mode that utilizes lateral electric field. Also, the liquid crystal display device may be not only the transmission type but also a reflection type or a combination of the reflection and transmission types. The active device may be not only the polysilicon TFT but also amorphous silicon TFT or other active devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-201182 | Jul 2005 | JP | national |
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| 4795239 | Yamashita et al. | Jan 1989 | A |
| 7312638 | Kobashi | Dec 2007 | B2 |
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| Number | Date | Country |
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| 62-49399 | Mar 1987 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20070008266 A1 | Jan 2007 | US |
