JP5515465B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to an active matrix liquid crystal display device, a driving circuit for the liquid crystal display device, and a driving method for the liquid crystal display device.

  In recent years, a liquid crystal display device of LCOS (Liquid Crystal on Silicon) type is often used as a central part for projecting images in projector devices and projection televisions. This LCOS liquid crystal display device has a structure in which a transparent electrode, a liquid crystal layer, a reflective electrode arranged in a matrix, a liquid crystal driving element in which a liquid crystal driving circuit is formed on a silicon substrate, and the like overlap.

  In this liquid crystal display device, pixels are arranged at intersections of a plurality of data lines (column signal lines) and a plurality of gate lines (row scanning lines). As shown in FIG. 10, each pixel includes a pixel selection transistor Q, a signal holding capacitor Cs, and a reflective electrode PE. The pixel selection transistor Q has a gate connected to a gate line (row scanning line) G and a drain connected to a data line (column signal line) D. Further, as shown in FIG. 10, the liquid crystal element LC has a configuration in which a liquid crystal display (liquid crystal layer) LCM is sandwiched between a reflective electrode (pixel electrode) PE and a counter electrode (common electrode) CE facing each other. ing.

  The liquid crystal element LC controls the light modulation rate of the liquid crystal display LCM by applying a fixed voltage Vcom to the common electrode CE and supplying various voltages according to the video signal to the reflective electrode (pixel electrode) PE. And display as video. In general, since the liquid crystal element can be AC-driven for long-term stability of reliability, the reflection electrode (pixel electrode) PE has a light modulation rate according to the video signal with respect to the fixed voltage Vcom of the common electrode CE. AC driving is performed by alternately applying positive and negative voltages that are equal to each other.

  In some cases, for the purpose of expanding the dynamic range of video signals, there is an application example in which the voltage of the counter electrode is switched according to the timing of driving with the positive and negative voltages, but the basic idea is the same It is.

  In the conventional liquid crystal display device, the video signal is normally written to each pixel once per frame, and the video signal on the positive side and the negative side is signaled alternately with respect to the common electrode CE every frame. After writing to the holding capacitor Cs, the holding voltage is applied to the reflective electrode (pixel electrode) PE, and the liquid crystal element LC is AC driven. In this case, there is an example of double speed driving in which the liquid crystal is AC driven at a frequency twice as high as the writing frequency, but the frequency is about 60 Hz to 120 Hz, and is not a high frequency in any case.

  On the other hand, if the direct current component between the reflective electrode (pixel electrode) PE and the common electrode CE can be reduced to zero by driving the liquid crystal element with an alternating current at a higher frequency, it leads to improved reliability such as prevention of burn-in. The display quality of the image is also improved.

  Until now, prevention of deterioration of written signals such as countermeasures against feedthrough caused by parasitic capacitance of the pixel selection transistor (for example, refer to Patent Document 1) and countermeasures for leakage of a storage capacitor (for example, refer to Patent Document 2). A method is disclosed. However, it seems that efforts to drive alternating current at higher frequencies have not been studied much.

  For each of a plurality of pixels connected to the same scanning line, the storage capacitor of each pixel is alternately connected to the storage capacitor line corresponding to the scanning line and another storage capacitor line corresponding to the adjacent scanning line. Inverting the compensation voltage for compensating the DC component between the pixel electrode and the counter electrode for each storage capacitor line causes image quality degradation due to potential fluctuations of the common electrode line and the common electrode. Conventionally, a liquid crystal display device that prevents the above is known (see, for example, Patent Document 3).

JP 2006-10897 A JP 2002-250938 A JP 2004-354742 A

  As described above, it is desirable to AC drive the liquid crystal element at a high frequency as a means for improving the reliability such as prevention of burn-in of the liquid crystal element. Due to the increase in power consumption, it is difficult to write the positive and negative video signals alternately at high speed with respect to the counter electrode voltage. Conventionally, the AC drive frequency is only at the frame rate or about twice that frequency. Not.

  For example, when the vertical scanning frequency of the video signal is converted to a double speed of 120 Hz in the frame memory and the polarity of the video signal is inverted every vertical scanning cycle, the AC driving frequency of the liquid crystal element is 1/2 that of 60 Hz. Thus, under the driving conditions where the AC driving frequency of the liquid crystal element is on the order of several tens of Hz to 100 Hz, compared with the case where the liquid crystal is driven with an AC voltage having a high frequency on the order of several kHz or more, reliability related to liquid crystal characteristics, There is a problem that it is difficult to ensure stability and yield.

  Further, in the liquid crystal display device described in Patent Document 3, the polarity of the compensation voltage can be reversed only for each frame, and the image signal voltage has two types of voltages, positive and negative, with respect to the common electrode voltage Vcom. is necessary.

  Furthermore, when the liquid crystal element is configured to be AC driven at a higher speed than before, it is desired to reduce the increase in circuit scale and power consumption as much as possible and to improve the yield.

  The present invention has been made in view of the above points. When the liquid crystal element is configured to be driven by alternating current at a higher speed than before, the pixel size can be reduced, the polarity switching driver can be reduced, and the power consumption can be reduced. An object of the present invention is to provide a liquid crystal display device that can reduce crosstalk with the polarity switching wiring and eliminate the vertical luminance difference for each line.

In order to achieve the above object, the liquid crystal display device of the present invention is provided at an intersection where a plurality of sets of data lines each composed of two data lines intersect with a plurality of row scanning lines. A plurality of pixels, each of the plurality of pixels,
A liquid crystal element in which a liquid crystal layer is sandwiched between an opposing pixel electrode and a common electrode, and a positive video signal supplied via one of a pair of two data lines are sampled and held for a certain period. 1 sampling and holding means, a second sampling and holding means for sampling and holding a negative video signal supplied via the other of the pair of two data lines, and a first polarity switching The positive video signal voltage held by the first sampling and holding means is applied to the pixel electrode by the first gate control signal supplied through the wiring, and the first video signal voltage supplied through the second polarity switching wiring is supplied. The operation of applying the negative video signal voltage held by the second sampling and holding means to the pixel electrode in accordance with the second gate control signal is based on the first and second gate control signals. And switching means for alternately performing switching at a predetermined cycle shorter than the inspection cycle, and first and second gates for supplying the first and second gate control signals to a plurality of adjacent two lines of pixels. The two polarity switching wirings are respectively shared.

In order to achieve the above object, the liquid crystal display device of the present invention is provided at an intersection where a plurality of data lines each composed of two data lines intersect with a plurality of row scanning lines. A plurality of pixels, each of the plurality of pixels,
A liquid crystal element in which a liquid crystal layer is sandwiched between an opposing pixel electrode and a common electrode, and a positive video signal supplied via one of a pair of two data lines are sampled and held for a certain period. 1 sampling and holding means, a second sampling and holding means for sampling and holding a negative video signal supplied via the other of the pair of two data lines, and a first polarity switching The positive video signal voltage held by the first sampling and holding means is applied to the pixel electrode by the first gate control signal supplied through the wiring, and the first video signal voltage supplied through the second polarity switching wiring is supplied. The operation of applying the negative video signal voltage held by the second sampling and holding means to the pixel electrode in accordance with the second gate control signal is based on the first and second gate control signals. And switching means for alternately performing switching at a predetermined cycle shorter than the inspection cycle, and first and second gates for supplying the first and second gate control signals to a plurality of adjacent two lines of pixels. 2 polarity switching wirings are respectively shared, and a first fixed potential line is arranged between the pixel electrode wirings of the plurality of pixels in one of the adjacent two lines and the first polarity switching wiring. The second fixed potential line is arranged between the pixel electrode wiring of the plurality of pixels on the other line and the second polarity switching wiring.

  Here, the first and second polarity switching wirings and the first and second fixed potential lines may be formed as wirings in the same layer.

  According to the present invention, when the liquid crystal element is configured to be driven by alternating current at a higher speed than before, the polarity switching wiring can be shared by two pixels, thereby reducing the size of the pixel, reducing the polarity switching driver, and reducing the power consumption. it can. Further, according to the present invention, it is possible to reduce crosstalk with the polarity switching wiring and eliminate the vertical luminance difference for each line.

It is a circuit block diagram of the pixel circuit of 1st Embodiment of the liquid crystal display device of this invention. It is a circuit diagram of the basic pixel circuit of one pixel of the liquid crystal display device of the present invention. 3 is a timing chart for explaining the operation of FIG. 2. It is a wave form diagram explaining a positive video signal and a negative video signal. 3 is a timing chart of each part of the pixel circuit shown in FIG. 1. It is a figure which shows the image of the striped pattern which may generate | occur | produce in the pixel circuit shown in FIG. It is a circuit block diagram of the pixel circuit of 2nd Embodiment of the liquid crystal display device of this invention. It is a partial cross section figure of 2nd Embodiment of the liquid crystal display device of this invention. 8 is a timing chart of each part of the pixel circuit shown in FIG. 7. It is a block diagram of an example of one pixel of a liquid crystal display device.

  FIG. 1 shows a circuit configuration diagram of a pixel circuit of a first embodiment of a liquid crystal display device according to the present invention. The pixel circuit of the present embodiment is formed by inverting the basic pixel circuit of one pixel of the active matrix liquid crystal display device shown in FIG. 2 by inverting the upper and lower pixels and sharing the polarity switching wiring. First, the configuration and operation of the basic pixel circuit in FIG. 2 will be described.

  In FIG. 2, the basic pixel circuit includes pixel selection switching transistors Q1 and Q2 for writing positive and negative video signals, and two independent storage capacitors that hold video signal voltages of respective polarities in parallel. Cs1 and Cs2, transistors Q3 and Q4 whose gates are connected to the signal storage nodes of the holding capacitors Cs1 and Cs2, transistors Q5 and Q6 whose drains are connected to the sources of the transistors Q3 and Q4, and a transistor Q7 And the liquid crystal element LC.

  The transistor Q3 forms a first impedance conversion buffer (source follower) circuit. Similarly, the transistor Q4 constitutes a second impedance conversion buffer (source follower) circuit. The output terminals (the sources of Q5 and Q6) of the first and second impedance conversion buffer circuits are connected to the drains of the transistors Q5 and Q6. The transistors Q5 and Q6 are polarity switching switching transistors that can individually control conduction / non-conduction of the impedance conversion buffer circuit output with respect to the pixel electrode PE.

  The drain of the constant current load transistor Q7 of the source follower circuit is connected to a connection point between the sources of the transistors Q5 and Q6 and the pixel electrode PE of the liquid crystal element LC. The transistor Q7 is configured to function in common as a constant current load element of both the source follower circuits (Q3, Q4). Like the conventional liquid crystal element shown in FIG. 10, the liquid crystal element LC has a configuration in which a display body (liquid crystal layer) LCM is sandwiched between a pixel electrode PE and a common electrode CE facing each other.

  The data line of the pixel portion is composed of a pair of positive D + and negative D− for each pixel circuit, and supplied with video signals having different polarities sampled by a data line driving circuit (not shown). The The input drain terminals of the write switching transistors Q1 and Q2 are connected to the data lines Di + and Di-, respectively, and the gate terminals are connected to the row scanning line Gj for the same row. When a scanning pulse is supplied from a vertical scanning circuit (not shown), the writing switching transistors Q1 and Q2 are simultaneously turned on, and positive and negative video signal voltages are accumulated in the holding capacitors Cs1 and Cs2, respectively.

  The gate of the constant current source load transistor Q7 is commonly wired as the wiring B in the row direction for the same row pixel, and the bias control of the constant current load is possible. The input resistance of each source follower circuit of the MOS transistors Q3 and Q4 is almost infinite, and the charge accumulated in the storage capacitor terminal does not leak as in the conventional active matrix liquid crystal display device, and the signal is output after one vertical scanning period. Is held until it is newly written.

  The switching transistors Q5 and Q6 switch and send the output signal of the source follower circuit to the liquid crystal element LC including the pixel electrode PE, the liquid crystal display LCM, and the common electrode CE. The gate terminals of the transistor Q5 that switches the positive video signal and the transistor Q6 that switches the negative video signal are independent, and each is wired as wirings S + and S− in the row direction for the same row pixel. ing. By alternately sending on / off control pulses to the wirings S + and S−, the switching transistors Q5 and Q6 are alternately turned on, and a liquid crystal drive signal that is inverted to positive polarity and negative polarity can be given to the pixel drive unit. . The pixel circuit shown in FIG. 2 has a polarity reversal function in the circuit itself, and can be driven at a high frequency without restriction of the vertical scanning frequency by controlling the switching transistors Q5 and Q6 at high speed. .

  Next, an outline of AC drive control of the active matrix liquid crystal display device according to the present invention will be described with reference to the timing chart of FIG. 3A is a vertical synchronizing signal that is a reference for vertical scanning of the video signal, and FIG. 3B is supplied to the gate of the constant current load transistor Q7 of the source follower buffer in the pixel circuit of FIGS. FIG. 3C shows the load characteristic control signal, FIG. 3C shows the gate control signal of the switching transistor Q5 shown in FIG. 2 that transfers the positive video signal through the wiring S +, and FIG. 3D shows the negative video signal through the wiring S−. It is a gate control signal of the switching transistor Q6 shown in FIG.

  FIG. 4 shows the relationship from the black level to the white level of the positive video signal I and the negative video signal II written to the pixel. The positive video signal I has a black level when the level is minimum and a white level when the level is maximum, whereas the negative video signal II has a white level when the level is minimum and a black level when the level is maximum. The inversion center of the positive video signal I and the negative video signal II is indicated by III.

  In FIG. 4, the positive video signal I is a black level when the level is minimum and a white level when the level is maximum, whereas the negative video signal II is a white level when the level is minimum and when the level is maximum. Although the case of the black level is shown, in the pixel circuit of the liquid crystal display device of the present invention, the positive video signal is the white level when the level is minimum, the black level when the level is maximum, and the negative video signal is the level. The black level may be at the minimum, and the white level at the maximum.

  In the pixel circuit shown in FIG. 2, the positive polarity side switching transistor Q5 is turned on while the gate control signal of the wiring S + shown in FIG. When the signal is set to the high level as shown in FIG. 3B, the source follower buffer circuit becomes active, and the pixel electrode PE node is charged to the positive video signal level. When the potential of the pixel electrode PE is fully charged, the load characteristic control signal of the wiring B is set to a low level, and at that time, the gate control signal of the wiring S + is also switched to a low level. PE becomes floating, and a positive drive voltage is held in the liquid crystal capacitor.

  On the other hand, when the gate control signal of the wiring S− shown in FIG. 3D is at a high level, the negative polarity side switching transistor Q6 is turned on, and the load characteristic control signal supplied to the wiring B during this period is shown in FIG. ), The source follower buffer circuit becomes active and the pixel electrode PE node is charged to a negative video signal level. When the potential of the pixel electrode PE is fully charged, the load characteristic control signal of the wiring B is set to low level, and the gate control signal of the wiring S- is also switched to low level at that time, the pixel electrode PE becomes floating, and the negative drive voltage is held in the liquid crystal capacitor.

  In the following, the pixel electrode PE of the liquid crystal element has a positive polarity and a negative polarity by repeating the operation of intermittently activating the constant current load transistor Q7 in synchronization with the switching in which the switching transistors Q5 and Q6 are alternately turned on. A drive voltage VPE converted into an alternating current with each video signal is applied as shown in FIG.

  The pixel circuit of FIG. 2 is configured to supply a voltage via a source follower buffer circuit rather than directly transferring the retained charge to the pixel driving unit, so that the charge can be recharged even when repeated charge / discharge with positive / negative polarity is performed. There is no problem of neutralization, and driving without attenuation of the voltage level can be realized even if the polarity is switched many times.

  Further, Vcom shown in FIG. 3F represents a voltage applied to the common electrode CE formed on the counter substrate of the liquid crystal display device. The substantial AC drive voltage of the liquid crystal display LCM is a difference voltage between the applied voltage Vcom of the common electrode CE and the applied voltage VPE of the pixel electrode PE. In the present embodiment, as shown in FIG. 3F, the applied voltage Vcom of the common electrode CE is synchronized with pixel polarity switching with respect to a reference level that is substantially equal to the inversion reference level Vc of the pixel electrode voltage VPE. Inverted. As a result, the absolute value of the potential difference between the applied voltage Vcom of the common electrode CE and the applied voltage VPE of the pixel electrode PE is always the same, and the liquid crystal display LCM has an AC voltage having no DC component as shown in FIG. VLC is applied.

  As described above, in the present embodiment in which the driving shown in the timing chart of FIG. 3 is performed on the pixel circuit of FIG. 2, the application voltage Vcom of the common electrode CE is switched in the opposite phase to the pixel electrode voltage VPE, thereby The amplitude of the drive voltage VPE on the (PE) side can be reduced to about 1/2 or less. As a result, the required breakdown voltage of the transistors constituting the pixel circuit and the peripheral scanning circuit is significantly reduced, and a special high breakdown voltage structure and process need not be applied, and the manufacturing cost can be reduced. In addition, in the pixel driving method of the present embodiment, since a driving unit such as a pixel circuit can be configured with a low breakdown voltage and small transistor as described above, a liquid crystal display device with a higher pixel density can be realized, and the transistor breakdown voltage can be reduced. Since it is possible to employ a transistor having a high driving capability per unit channel width, it is possible to easily cope with a high-speed driving operation.

  In consideration of the reduction in current consumption in the liquid crystal display device, the constant current load transistor Q7 of the source follower buffer circuit is always active by using the load characteristic control signal of the wiring B as a pulse train as shown in FIG. Instead, control is performed so that the polarity switching switching transistors Q5 and Q6 become active only during a limited period of the conduction period. For example, even if the current of the steady source follower buffer circuit per pixel circuit is a very small current of 1 μA, a large current is consumed under the condition that all the pixels of the liquid crystal display device constantly consume the current. There is a problem that. For example, in a full high-definition (2 million pixels) liquid crystal display device, the current consumption reaches 2 A.

  Therefore, in the present embodiment, as shown in FIGS. 3B to 3D, the polarity switching switching transistor in which the gate control signal supplied through the polarity switching wirings S + and S− is at a high level. Only during the conduction period of Q5 and Q6, the load characteristic control signal supplied via the wiring B is set to the high level to limit the driving period of the constant current load transistor Q7 of the source follower buffer circuit. As a result, immediately after the pixel electrode voltage VPE of the liquid crystal element is charged / discharged to the target level as shown in FIG. 3D, the load characteristic control signal immediately becomes low level as shown in FIG. Then, the constant current load transistor Q7 is turned off, and the current of the source follower buffer circuit is stopped. Therefore, according to the present embodiment, it is possible to suppress a substantial current consumption while having a configuration in which a buffer is provided for all pixels.

  However, since the pixel circuit shown in FIG. 2 requires seven transistors Q1 to Q7 in one pixel, the number of wirings for supplying signals to each of the transistors Q1 to Q7 is large, and the pixel size is increased. End up.

  Therefore, the liquid crystal display device of the present embodiment shown in FIG. 1 is formed by inverting the upper and lower two pixels (two pixels adjacent in the vertical direction of two adjacent lines), and switching the polarity switching wirings S + and S−. Are shared by these two pixels, thereby reducing the overall pixel size.

  In FIG. 1, each of the upper and lower two pixel circuits of the liquid crystal display device of the present embodiment has basically the same circuit configuration as the pixel circuit shown in FIG. 2, and the same components as in FIG. A reference numeral is attached to one pixel circuit, and a suffix 1 is attached to the reference numeral, and a suffix 2 is attached to the other pixel circuit.

  That is, for example, the pixel circuit of one pixel on the upper side holds switching transistors Q11 and Q21 for writing positive and negative pixel signals and image signal voltages of the respective polarities in parallel as shown in FIG. Two independent holding capacitors Cs11 and Cs21, and respective impedance conversion buffer (source follower) circuits by transistors Q31 and Q41 connected to the respective signal storage nodes of the holding capacitors Cs11 and Cs21, and the impedance conversion buffer Two polarity switching switching transistors Q51 and Q61, which are connected between the output terminal of the circuit and the pixel electrode PE and can individually control the conduction / non-conduction of the buffer output with respect to the pixel electrode, and the constant current load transistor Q71 It is configured.

  Further, as shown in FIG. 1, the pixel circuit of the lower pixel holds in parallel the switching transistors Q12 and Q22 for writing the positive and negative pixel signals and the image signal voltages of the respective polarities. Two independent holding capacitors Cs12 and Cs22, and respective impedance conversion buffer (source follower) circuits by transistors Q32 and Q42 connected to respective signal storage nodes of the holding capacitors Cs12 and Cs22, and the impedance conversion buffer Two switching transistors Q52 and Q62 for switching the polarity, which are connected between the output terminal of the circuit and the pixel electrode PE and can individually control the conduction / non-conduction of the buffer output with respect to the pixel electrode, and the constant current load transistor Q72 It is configured.

  The data line of the pixel portion is composed of a pair of positive D + and negative D− for each pixel circuit, and supplied with video signals having different polarities sampled by a data line driving circuit (not shown). The The input drain terminals of the write switching transistors Q11, Q12 are each connected to the data line Di +, and the input drain terminals of the write switching transistors Q21, Q22 are each connected to the data line Di-. The gate terminals of the switching transistors Q11 and Q21 of the upper pixel circuit are connected to the row scanning line Gji− for the same row, and the gate terminals of the switching transistors Q12 and Q22 of the lower pixel circuit are the row scanning line Gji + for the same row. It is connected to the.

  When a scanning pulse is supplied to the row scanning line Gji− from a vertical scanning circuit (not shown), the write switching transistors Q11 and Q21 are simultaneously turned on, and positive and negative video signal voltages are respectively applied to the holding capacitors Cs11 and Cs21. Accumulated. When the scanning pulse is supplied to the adjacent row scanning line Gji +, the write switching transistors Q12 and Q22 are simultaneously turned on, and positive and negative video signal voltages are accumulated in the holding capacitors Cs12 and Cs22, respectively. The

  The transistor Q71 has a drain connected to the electrode wiring 11 of the pixel electrode PE of the liquid crystal element of the upper pixel after the polarity switching switching transistors Q51 and Q61, and has both positive and negative source follower circuits (Q31, Q41). It is configured to function in common as a constant current load element. The constant current source load transistor Q71 has a gate commonly connected to a line Bi- in the row direction for the same row pixel, and can control the bias of the constant current load. Similarly, the transistor Q72 has a drain connected to the electrode wiring 12 of the pixel electrode PE of the liquid crystal element of the lower pixel after the polarity switching transistors Q52 and Q62, and has a positive / negative source follower circuit (Q32, Q Q42) It is configured to function in common as both constant current load elements. The constant current source load transistor Q72 has a gate commonly connected to the line Bi + in the row direction for the same row pixel, and is configured to be capable of bias control of the constant current load.

  On the other hand, in order to transfer the positive video signals held in the signal holding capacitors Cs11 and Cs12, the polarity switching wiring S + for transmitting the first gate control signal for controlling the transistors Q51 and Q52 to be on is a transistor of two upper and lower pixels. Commonly connected to the gates of Q51 and Q52. In addition, the polarity switching wiring S− for transmitting the second gate control signal for controlling the transistors Q61 and Q62 to be turned on in order to transfer the negative video signals held in the signal holding capacitors Cs21 and Cs22 is a transistor of two upper and lower pixels. Commonly connected to the gates of Q61 and Q62.

  The input resistance of each source follower circuit of the MOS transistors Q31, Q41, Q32, and Q42 is almost infinite, and the charge accumulated in the storage capacitor terminal does not leak as in the conventional active matrix type liquid crystal display device. The signal is held until a new signal is written after the scanning period.

  FIG. 5 is a timing chart for explaining an outline of AC drive control of the pixel circuit of the first embodiment of the liquid crystal display device of the present invention shown in FIG. FIG. 5A shows a vertical synchronizing signal which is a reference for vertical scanning of a video signal, and FIG. 5B shows a load supplied to the gate of the constant current load transistor Q71 or Q72 of the source follower buffer in the pixel circuit of FIG. FIG. 5C shows the characteristic control signal, FIG. 5C shows the gate control signal of the switching transistors Q51 and Q52 shown in FIG. 1 that transfers the positive video signal through the wiring S +, and FIG. 5D shows the negative video through the wiring S-. This is a gate control signal for the switching transistors Q61 and Q62 shown in FIG.

  FIG. 5G shows the voltage Vcom applied to the common electrode formed on the counter substrate of the liquid crystal element. As shown in the figure, the applied voltage Vcom to the common electrode is inverted in synchronization with the pixel polarity switching with respect to a reference level that is substantially equal to the inversion reference Vc of the pixel electrode potential. In the present embodiment, the upper pixel circuit and the lower pixel circuit are selected at intervals of one horizontal scanning period, and the same driving as described with reference to FIGS. 2 and 3 is performed based on the timing chart of FIG. Done.

Thus, according to the present embodiment, the AC drive frequency of the liquid crystal element can be freely set in the inversion control cycle in the pixel circuit, regardless of the vertical scanning frequency. For example, it is assumed that the vertical scanning frequency is 60 Hz used for a general television image signal, and the number of full periodic high-definition vertical scanning lines is 1125 lines. If the polarity of the pixel circuit is switched at a cycle of about 15 line periods, the AC drive frequency of the liquid crystal element is 60 (Hz) × 1125 ÷ (15 × 2) = 2.25 (KHz).
Thus, the liquid crystal driving frequency can be dramatically increased as compared with the conventional liquid crystal display device. As a result, it is possible to greatly improve the reliability and stability when the AC drive of the liquid crystal element is at a low frequency and the display quality deterioration such as a stain.

  Further, in this embodiment, the upper and lower two pixels are inverted and formed so that the polarity switching wirings S + and S− are shared by the upper and lower two pixels. Therefore, the polarity switching wirings S + and S− are upper and lower. Since one pixel is sufficient for each of the two pixels, two pixels can be reduced. In addition, since the polarity switching wirings S + and S− may be switched at the same time for both the upper and lower pixels, there is no problem even if they are shared.

  By doing so, according to the present embodiment, for example, a pixel pitch of 9 μm can be reduced to a pixel pitch of 8 μm. Furthermore, according to the present embodiment, since the driver for driving the polarity switching wirings S + and S− may be shared by two pixels, the number of polarity switching drivers can be halved. By reducing the number of drivers for polarity switching, power consumption can be reduced and the yield can be improved.

  However, as shown in FIG. 1, when the upper and lower two pixels are inverted and the polarity switching wirings S + and S- are shared, the two polarity switching wirings S + and S- Since the crosstalk amounts are different, there is a possibility that the luminance of adjacent two upper and lower pixels changes, resulting in a stripe pattern for each line.

  In FIG. 1, the pixel electrode wiring (UP_pixel electrode wiring) 11 of the upper pixel has a large amount of crosstalk with the polarity switching wiring S− because the distance to the polarity switching wiring S− is short. On the other hand, the pixel electrode wiring (DW_pixel electrode wiring) 12 of the lower pixel has a large amount of crosstalk with the polarity switching wiring S + because it is close to the polarity switching wiring S +.

  Since the UP_pixel electrode wiring 11 has a large amount of crosstalk with the polarity switching wiring S-, at the same time when the gate control signal of S- is turned off (low level), it largely crosses in the same direction as the waveform of the gate control signal. Talk. As a result, the amplitude of the waveform of the signal UP_VPE of the UP_pixel electrode wiring 11 changes as shown in FIG.

  On the other hand, since the DW_pixel electrode wiring 12 has a large amount of crosstalk with the polarity switching wiring S +, at the same time when the gate control signal of S + is turned off (low level), it greatly increases in the same direction as the waveform of the gate control signal. Cross talk to. As a result, the amplitude of the waveform of the signal DW_VPE of the DW_pixel electrode wiring 12 changes as shown in FIG.

  As a result, even when the same signal is written to the UP_pixel electrode wiring 11 and the DW_pixel electrode wiring 12, the signal waveform of each pixel electrode is different, the amplitude of the UP_VPE signal waveform is increased, and the DW_VPE signal The amplitude of the waveform is reduced. On the other hand, the common electrode voltage Vcom is common to the upper and lower two pixels. For this reason, the driving voltage of the liquid crystal element connected to the UP_pixel electrode wiring 11 is increased, and the luminance is increased (brighter). Further, the driving voltage of the liquid crystal elements in the adjacent lines connected to the DW_pixel electrode wiring 12 is reduced, and the luminance is lowered (darkened). For this reason, the display screen has each line as shown in FIG. Therefore, a luminance difference will occur.

  Therefore, it is important to prevent potential fluctuations in the pixel electrode wiring and to prevent crosstalk with the polarity switching wiring in question.

  In FIG. 1, the UP_pixel electrode wiring 11 crosstalks with the row scanning line Gji−, and the DW_pixel electrode wiring 12 also crosstalks with the row scanning line Gji +. . However, the row scanning lines Gji + and Gji− are wiring for each row, and the row scanning lines Gji + and Gji− are turned on at the beginning of the horizontal scanning and turned off at the end of the horizontal scanning. Cross talk to. Therefore, since the displayed picture is not recognized as a pattern, the crosstalk between the row scanning lines Gji + and Gji− does not cause a problem.

  FIG. 7 is a circuit diagram of a pixel circuit according to the second embodiment of the liquid crystal display device of the present invention, which is configured to prevent crosstalk between the pixel electrode wiring and the polarity switching wirings S + and S−. A block diagram is shown. In the figure, the same components as those in FIG. As shown in FIG. 7, in this embodiment, in order to prevent crosstalk between the pixel electrode wirings 11 and 12 and the polarity switching wirings S− and S +, a fixed potential line 21 connected to a fixed potential. Is inserted between the polarity switching wiring S + and the pixel electrode wiring 11, and the fixed potential line 22 connected to the fixed potential is inserted between the polarity switching wiring S− and the pixel electrode wiring 12. .

  Specifically, by inserting the fixed potential lines 21 and 22 between the polarity switching lines S− and S + formed by the same layer wiring and the pixel electrode wirings 11 and 12, the polarity formed by the same layer The parasitic capacitance between the switching wiring and the pixel electrode is reduced, and the pixel electrode is prevented from being shaken by the polarity switching wiring.

  FIG. 8 shows a partial cross-sectional view of the second embodiment of the liquid crystal display device of the present invention shown in FIG. In the figure, two MOS transistors 101 and 102 separated by a field oxide film 103 are formed on the surface of a P-type silicon substrate 100. Each of the transistors 101 and 102 is connected to the first metal 105 formed through the first interlayer film 104, and further, the DW_pixel electrode wiring 12 formed on the second interlayer film 106 through the first metal 105. Is electrically connected. The transistors 101 and 102 correspond to the transistors Q52 and Q62 shown in FIG. 7 (one of Q52 and Q62 may be the transistor Q72).

  In addition to the DW_pixel electrode wiring 12 described above, the second metal 107 formed on the second interlayer film 106 includes the fixed potential lines 21 and 22 and the polarity switching wiring 109 (S +) shown in FIG. 110 (S−), row scanning line 111 (Gji +), wiring 112 for load characteristic control signal Bi +, and the like. Here, the fixed potential line 22 is disposed between the DW_pixel electrode wiring 12 and the polarity switching wiring 109 (S +). In addition, the polarity switching wirings 109 (S +) and 110 (S−) are arranged adjacent to each other. The polarity switching wirings 109 (S +) and 110 (S−) are shared with adjacent pixels on the left that are not shown.

  Furthermore, the DW_pixel electrode wiring 12 includes a third interlayer film 113 covering the second metal 107 and the fourth interlayer film covering the light shielding film (third metal) 114 formed on the third interlayer film 113. 115 is electrically connected to the DW_pixel electrode (fourth metal) 116 through a via hole penetrating each of 115. On the DW_pixel electrode (fourth metal) 116, a liquid crystal layer 117 and a common electrode 118 are stacked. The common electrode 118 is a transparent electrode formed so as to be opposed to the DW_pixel electrode (fourth metal) 116. Light from a backlight (not shown) is transmitted through the common electrode 118 and the liquid crystal layer 117, is incident on the DW_pixel electrode (fourth metal) 116, and is reflected.

  FIG. 9 is a timing chart for explaining the outline of AC drive control of the pixel circuit of the second embodiment of the liquid crystal display device of the present invention shown in FIG. FIG. 9A shows a vertical synchronizing signal that is a reference for vertical scanning of a video signal, and FIG. 9B shows a load supplied to the gate of the constant current load transistor Q71 or Q72 of the source follower buffer in the pixel circuit of FIG. FIG. 9C shows the characteristic control signal, FIG. 9C shows the gate control signal of the switching transistors Q51 and Q52 shown in FIG. 7 for transferring the positive video signal through the wiring S +, and FIG. 9D shows the negative video through the wiring S-. This is a gate control signal for the switching transistors Q61 and Q62 shown in FIG.

  FIG. 9G shows the voltage Vcom applied to the common electrode formed on the counter substrate of the liquid crystal element. As shown in the figure, the applied voltage Vcom to the common electrode is inverted in synchronization with the pixel polarity switching with respect to a reference level that is substantially equal to the inversion reference Vc of the pixel electrode potential. In the present embodiment, the upper pixel circuit and the lower pixel circuit are selected at intervals of one horizontal scanning period, and the same driving as described with reference to FIGS. 2 and 3 is performed based on the timing chart of FIG. Done.

  Thus, according to the present embodiment, as in the first embodiment shown in FIG. 1, the AC drive frequency of the liquid crystal element is increased, and the display quality such as reliability / stability and stains is reduced. Significant improvement, downsizing of the entire device, and low power consumption can be realized. Furthermore, in the present embodiment, the amplitude fluctuation of the pixel electrode voltage due to crosstalk between the pixel electrode wiring and the polarity switching wirings S + and S− that may occur in the first embodiment is changed to a fixed potential. By preventing the arrangement of the lines 21 and 22, it is possible to eliminate the vertical luminance difference for each line on the display screen.

  Next, the effect of preventing the amplitude fluctuation of the pixel electrode voltage due to the crosstalk will be described in more detail. As shown in FIG. 8, in the present embodiment, the fixed potential line 22 is arranged between the polarity switching wiring 109 (S +) formed of the second metal 107 and the DW_pixel electrode wiring 12. The horizontal electric field between the polarity switching wiring 109 (S +) and the DW_pixel electrode wiring 12 is cut off. The lateral electric field of the polarity switching wiring 109 (S +) is generated in the polarity switching wiring 110 (S−) and the fixed potential line 22, and the lateral electric field of the DW_pixel electrode wiring 12 is fixed in the fixed potential line 22 and the GND line 113. Has occurred.

  As a result, a lateral electric field generated between the polarity switching wiring 109 (S +) and the DW_pixel electrode wiring 12 becomes very small, and the polarity switching wiring 110 (S−) and the DW_pixel electrode wiring 12 are not connected. The difference between the generated electric field and the electric field is not so much. As a result, the pixel electrode (DW_pixel electrode wiring 12) of the lower pixel has approximately the same crosstalk amount with the polarity switching wiring S + and crosstalk amount with the polarity switching wiring S−.

  That is, in FIG. 7, the pixel electrode (UP_pixel electrode wiring 11) of the upper pixel has a small difference between the crosstalk amount with the polarity switching wiring S− and the crosstalk amount with the polarity switching wiring S +. . The pixel electrode (DW_pixel electrode wiring 12) of the lower pixel has a small difference between the crosstalk amount with the polarity switching wiring S + and the crosstalk amount with the polarity switching wiring S−. Therefore, the pixel electrode potentials that should be originally held in the upper and lower two pixels are substantially equal.

  In this way, in order to reduce the size of the pixel, when the upper and lower two pixels are inverted as shown in FIG. 7 and the polarity switching wirings S + and S− are shared by the upper and lower two pixels, the polarity switching wiring S− The sampled potential of the UP_pixel electrode wiring 11 is not fluctuated due to the potential fluctuation caused by the transmitted gate control signal. Further, the potential of the sampled DW_pixel electrode wiring 12 is not shaken by the potential fluctuation transmitted through the polarity switching wiring S +.

  Specifically, the waveform of the signal UP_VPE of the UP_pixel electrode wiring 11 is as shown in FIG. 9E, and the waveform of the signal DW_VPE of the DW_pixel electrode wiring 12 is as shown in FIG. Since both signal waveforms are substantially equal and amplitudes are also equal, the difference in luminance between the upper and lower lines is eliminated. For this reason, the brightness change of the adjacent upper and lower pixels is eliminated, and it is improved so that the stripe pattern for each line as shown in FIG. 6 does not appear.

  In the embodiment of FIG. 7, any fixed voltage may be applied to the fixed potential lines 21 and 22. However, it is desirable to set between 0V and 5V supplied to the inside of the pixel circuit, and normally it is set to Vdd or GND. In the embodiment of FIG. 7, two fixed potential lines 21 and 22 are arranged next to the wiring S + and the wiring S− in two adjacent pixels, but the two fixed potential lines 21 and 22 are arranged. These potentials do not need to be the same. For example, Vdd may be supplied to the S + side fixed potential line 22, and GND may be supplied to the S− side fixed potential line 21.

Q1, Q11, Q12, Q2, Q21, Q22 Pixel selection switching transistors Q3, Q31, Q32, Q4, Q41, Q42 Source follower transistors Q5, Q51, Q52, Q6, Q61, Q62 Polarity switching transistors Q7, Q71, Q72 Constant current load transistor Cs1, Cs11, Cs12, Cs2, Cs21, Cs22 Signal holding capacity S-, S +, 109, 110 Polarity switching wiring Gj, Gji-, Gji + row scanning line D +, D- data line Bi +, Bi -Load characteristic control signal wiring LC Liquid crystal element PE Pixel electrode CE, 118 Common electrode LCM Display (Liquid crystal layer)
11 UP_Pixel electrode wiring 12 DW_Pixel electrode wiring 21, 22 Fixed voltage line 101, 102 Transistor 116 DW_Pixel electrode (fourth metal)
117 Liquid crystal layer

Claims (3)

A plurality of pixels provided at intersections where a plurality of sets of data lines each having two data lines and a plurality of row scanning lines intersect;
Each of the plurality of pixels is
A liquid crystal element in which a liquid crystal layer is sandwiched between a pixel electrode and a common electrode facing each other;
First sampling and holding means for sampling and holding a positive video signal supplied through one of the set of two data lines for a certain period;
Second sampling and holding means for sampling and holding a negative video signal supplied via the other of the pair of two data lines for a certain period;
A positive polarity video signal voltage held by the first sampling and holding means is applied to the pixel electrode by a first gate control signal supplied via a first polarity switching wiring, and a second polarity switching wiring is applied. An operation of applying a negative video signal voltage held by the second sampling and holding means to the pixel electrode by a second gate control signal supplied via the first and second gate control signals. And switching means for alternately performing switching at a predetermined cycle shorter than the vertical scanning cycle based on the first and second gate control signals to the adjacent two lines of pixels. A liquid crystal display device having a configuration in which the first and second polarity switching wirings are shared. A plurality of pixels provided at intersections where a plurality of sets of data lines each having two data lines and a plurality of row scanning lines intersect;
Each of the plurality of pixels is
A liquid crystal element in which a liquid crystal layer is sandwiched between a pixel electrode and a common electrode facing each other;
First sampling and holding means for sampling and holding a positive video signal supplied through one of the set of two data lines for a certain period;
Second sampling and holding means for sampling and holding a negative video signal supplied via the other of the pair of two data lines for a certain period;
A positive polarity video signal voltage held by the first sampling and holding means is applied to the pixel electrode by a first gate control signal supplied via a first polarity switching wiring, and a second polarity switching wiring is applied. An operation of applying a negative video signal voltage held by the second sampling and holding means to the pixel electrode by a second gate control signal supplied via the first and second gate control signals. And switching means for alternately performing switching at a predetermined cycle shorter than the vertical scanning cycle based on the first and second gate control signals to the adjacent two lines of pixels. Each of the first and second polarity switching wirings for sharing the pixel electric power of the plurality of pixels on one of the two adjacent lines. A first fixed potential line is disposed between the pole wiring and the first polarity switching wiring, and the pixel electrode wiring of the plurality of pixels on the other line and the second polarity switching wiring 2. A liquid crystal display device, characterized in that a second fixed potential line is arranged on the liquid crystal display device.   3. The liquid crystal display device according to claim 2, wherein the first and second polarity switching wirings and the first and second fixed potential lines are formed as wirings in the same layer.

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