LIQUID CRYSTAL DISPLAY DEVICE AND DRIVE METHOD THEREOF

A liquid crystal display device includes a display section including scanning lines, data lines, and pixel circuits, a scanning line drive circuit, a data line drive circuit, a first voltage output circuit, and a second voltage output circuit. The pixel circuit includes a liquid crystal capacitance having a pixel electrode, and applies one of a first voltage and a second voltage to the pixel electrode of the liquid crystal capacitance, in accordance with data written by driving the scanning line and the data line. The first voltage output circuit controls the first voltage to have a level that is more distant from the second voltage than a normal level, in accordance with a timing when a voltage of the pixel electrode changes. With this, a reflective type liquid crystal display device performing binary display and capable of preventing an afterimage caused by an orientation abnormality is provided.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a display device, especially to a liquid crystal display device and a drive method thereof.

Description of Related Art

A reflective type liquid crystal display device performing binary display is used in a display section of an electronic device, and the like. Apart from this, there is known a memory type liquid crystal display device including pixel circuits that digitally memorize written data. According to the memory type liquid crystal display device, a number of data writing to the pixel circuit can be reduced, and a power consumption of the liquid crystal display device can be reduced.

Related to the invention of the present application, Japanese Laid-Open Patent Publication H7-294881 discloses a liquid crystal display device that applies a plurality of voltages which are different from each other, to liquid crystal of each pixel in one frame period in order to improve a viewing angle characteristic.

The reflective type liquid crystal display device performing the binary display has a problem that an afterimage occurs in a display screen when a display image is switched.FIG. 15is a diagram showing how the afterimage occurs in a conventional liquid crystal display device.FIG. 15describes a change of a display screen of a reflective type and memory type liquid crystal display device performing the binary display. When a screen Z1displaying a black triangle is switched to a screen Z2displaying a white triangle, it is desirable that the screen Z1be switched to the screen Z2immediately. However, in the conventional liquid crystal display device, there occurs an orientation abnormality called discrination, and a screen Zx including an afterimage (intermediate color portion in the triangle) is displayed between the screen Z1and the screen Z2.

FIG. 16is an enlarged diagram of a display section of the conventional liquid crystal display device.FIG. 16describes nine pixels arranged two-dimensionally. When an electric field is applied between a pixel electrode and a common electrode of a pixel Pc, orientations of liquid crystal molecules positioned at the pixel Pc are changed in accordance with the applied electric field. However, the liquid crystal molecules existing in a surrounding portion (broken line portion) of the pixel Pc is in a state of being difficult to move, because they are affected by electric fields from the pixel electrodes of neighboring pixels or neighboring wirings. Thus, even if the electric field is applied between the pixel electrode and the common electrode of the pixel Pc, the orientations of the liquid crystal molecules existing in the surrounding portion of the pixel Pc does not change immediately, and the orientation abnormality occurs. While the orientations are abnormal, the afterimage is visually recognized by an observer.

SUMMARY OF THE INVENTION

Therefore, providing a reflective type liquid crystal display device performing binary display capable of preventing an afterimage caused by an orientation abnormality is taken as a problem.

(1) A liquid crystal display device according to some embodiments of the present invention is a reflective type liquid crystal display device performing binary display, the device includes: a display section including scanning lines, data lines, and pixel circuits; a scanning line drive circuit configured to drive the scanning lines; a data line drive circuit configured to drive the data lines; a first voltage output circuit configured to output a first voltage; and a second voltage output circuit configured to output a second voltage, the pixel circuit includes a liquid crystal capacitance having a pixel electrode, and is configured to apply one of the first voltage and the second voltage to the pixel electrode in accordance with data written by driving the scanning line and the data line, and the first voltage output circuit is configured to control the first voltage to have a level that is more distant from the second voltage than a normal level, in accordance with a timing when a voltage of the pixel electrode changes.

(2) The liquid crystal display device according to some embodiments of the present invention has the configuration of above (1), and the first voltage output circuit is configured to make the first voltage change in an impulse manner in accordance with the timing.

(3) The liquid crystal display device according to some embodiments of the present invention has the configuration of above (1), and the first voltage output circuit is configured to make the first voltage change in a rectangular pulse manner in accordance with the timing.

(4) The liquid crystal display device according to some embodiments of the present invention has the configuration of above (1), and the second voltage output circuit is configured to control the second voltage to have a constant level in a frame period.

(5) The liquid crystal display device according to some embodiments of the present invention has the configuration of above (1), and the second voltage output circuit is configured to control the second voltage to have a level that is more distant from the first voltage than a normal level, in accordance with the timing.

(6) The liquid crystal display device according to some embodiments of the present invention has the configuration of above (5), and the second voltage output circuit is configured to make the second voltage change in an impulse manner in accordance with the timing.

(7) The liquid crystal display device according to some embodiments of the present invention has the configuration of above (5), and the second voltage output circuit is configured to make the second voltage change in a rectangular pulse manner in accordance with the timing.

(8) The liquid crystal display device according to some embodiments of the present invention has the configuration of above (1), and the first voltage output circuit is configured to output, as the first voltage, a same voltage to all of the pixel circuits, and to control the first voltage in accordance with all of the timings when the voltage of the pixel electrode changes.

(9) The liquid crystal display device according to some embodiments of the present invention has the configuration of above (1), the pixel circuits are classified into groups corresponding to the scanning lines, and the first voltage output circuit is configured to output, as the first voltage, voltages corresponding to the groups, and to control the first voltage that corresponds to the group, in accordance with a timing when the voltage of the pixel electrode in the pixel circuit in the group changes.

(10) The liquid crystal display device according to some embodiments of the present invention has the configuration of above (1), the device further includes a common electrode drive circuit configured to drive a common electrode of the liquid crystal capacitance, and the first voltage output circuit, the second voltage output circuit, and the common electrode drive circuit are configured to invert a level of a voltage output from each circuit, for each frame period.

(11) The liquid crystal display device according to some embodiments of the present invention has the configuration of above (1), and the pixel circuit includes: a write control transistor having a control terminal connected to the scanning line, and one conduction terminal connected to the data line; a memory circuit configured to memorize the data input through the write control transistor, and to output a control signal in accordance with the data;

and a voltage selection circuit configured to apply one of the first voltage and the second voltage to the pixel electrode according to the control signal.

(12) The liquid crystal display device according to some embodiments of the present invention has the configuration of above (11), the memory circuit is a flip-flop circuit configured to output, as the control signal, a first control signal and a second control signal that change complementarily, and the voltage selection circuit includes: a transistor configured to apply the first voltage to the pixel electrode according to the first control signal; a transistor configured to apply the second voltage to the pixel electrode according to the first control signal; a transistor configured to apply the first voltage to the pixel electrode according to the second control signal; and a transistor configured to apply the second voltage to the pixel electrode according to the second control signal.

(13) A drive method of a liquid crystal display device according to some embodiments of the present invention is a drive method of a reflective type liquid crystal display device having a display section including scanning lines, data lines, and pixel circuits, and performing binary display, the method includes: driving the scanning lines; driving the data lines; outputting a first voltage; and outputting a second voltage, the pixel circuit includes a liquid crystal capacitance having a pixel electrode, and is configured to apply one of the first voltage and the second voltage to the pixel electrode in accordance with data written by driving the scanning line and the data line, and in outputting the first voltage, the first voltage is controlled to have a level that is more distant from the second voltage than a normal level, in accordance with a timing when a voltage of the pixel electrode changes.

According to the above-described liquid crystal display device and the drive method thereof, by controlling the first voltage to have the level that is more distant from the second voltage than the normal level in accordance with the timing when the voltage of the pixel electrode changes, a trigger for liquid crystal molecules included in the liquid crystal capacitance to start to move can be provided. Therefore, orientations of the liquid crystal molecules existing in a surrounding portion of a pixel can be changed quickly, and an afterimage caused by an orientation abnormality that occurs when a display image is switched can be prevented.

These and other objects, features, modes and effects of the present invention will be more apparent from the following detailed description with reference to the attached drawings.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

FIG. 1is a block diagram showing a configuration of a liquid crystal display device according to a first embodiment. A liquid crystal display device10shown inFIG. 1includes a display section11, a display control circuit12, a scanning line drive circuit13, a data line drive circuit14, a white voltage output circuit15, a black voltage output circuit16, and a common electrode drive circuit17. The liquid crystal display device10is a reflective type and memory type liquid crystal display device performing binary display. In the following, it is assumed that m and n are integers not less than two, i is an integer not less than one and not more than m, and j is an integer not less than one and not more than n.

The display section11includes m scanning lines G1to Gm, n data lines D1to Dn, and (m×n) pixel circuits20. The scanning lines G1to Gm are arranged in parallel to each other. The data lines D1to Dn are arranged in parallel to each other so as to intersect with the scanning lines G1to Gm perpendicularly. The scanning lines G1to Gm and the data lines D1to Dn intersect at (m×n) points. The (m×n) pixel circuits20are two-dimensionally arranged corresponding to intersections of the scanning lines G1to Gm and the data lines D1to Dn. The pixel circuit20is connected to one scanning line and one data line.

The display control circuit12outputs a control signal CS1to the scanning line drive circuit13, and outputs a control signal CS2and a video signal VS to the data line drive circuit14. The control signal CS1includes a gate clock GCK, and the like. The scanning line drive circuit13drives the scanning lines G1to Gm based on the control signal CS1. The data line drive circuit14drives the data lines D1to Dn based on the control signal CS2and the video signal VS.

More specifically, the scanning line drive circuit13sequentially selects one scanning line from among the scanning lines G1to Gm based on the control signal CS1, and applies a write voltage (here, a high-level voltage) to the selected scanning line. With this, n pixel circuits20connected to the selected scanning line are selected collectively. The data line drive circuit14respectively applies n voltages in accordance with the video signal VS to the data lines D1to Dn based on the control signal CS2. With this, n pieces of data are written to the selected n pixel circuits20, respectively. The pixel circuit20corresponds to a pixel, and the data written to the pixel circuit20is binary data. A color of the pixel becomes white or black in accordance with the data written to the pixel circuit20.

The white voltage output circuit15outputs a voltage for displaying white (hereinafter referred to as a white voltage Vw). The black voltage output circuit16outputs a voltage for displaying black (hereinafter referred to as a black voltage Vb). The common electrode drive circuit17outputs a common electrode voltage Vcom. The pixel circuit includes a liquid crystal capacitance having a pixel electrode, and applies one of the white voltage Vw and the black voltage Vb to the pixel electrode in accordance with the data written by driving a scanning line Gi and a data line Dj. The common electrode drive circuit17drives a common electrode of the liquid crystal capacitance.

The display control circuit12outputs control signals (not shown) to the white voltage output circuit15, the black voltage output circuit16, and the common electrode drive circuit17. The white voltage output circuit15, the black voltage output circuit16, and the common electrode drive circuit17invert a level of a voltage output from each circuit, for each frame period based on the control signals output from the display control circuit12. With this, the liquid crystal display device10performs frame inversion drive in which a polarity of a voltage applied to the liquid crystal capacitance is inverted for each frame period.

A case where m=n=3 will be described below.FIG. 2is a diagram showing a detailed configuration of the liquid crystal display device10. As shown inFIG. 2, the pixel circuit20includes a pixel memory21, a voltage selection circuit22, and a liquid crystal capacitance23. A symbol Pij is depicted on the pixel memory21in the pixel circuit20in an i-th row and a j-th column. The pixel memory21in the pixel circuit20in the i-th row and the j-th column is connected to the scanning line Gi and the data line Dj, and outputs control signals SWij, SBij.

The white voltage Vw output from the white voltage output circuit15and the black voltage Vb output from the black voltage output circuit16are provided to two input terminals of the voltage selection circuit22, respectively. The control signals SWij, SBij are provided to two control terminals of the voltage selection circuit22, respectively. An output terminal of the voltage selection circuit22is connected to the pixel electrode (upper-side electrode inFIG. 2) of the liquid crystal capacitance23. The common electrode voltage Vcom output from the common electrode drive circuit17is applied to the common electrode of the liquid crystal capacitance23. A high-level voltage VDD and a low-level voltage VSS are supplied to the pixel circuit20using wirings not shown.

FIG. 3is a circuit diagram of the pixel circuit20.FIG. 3describes the pixel circuit20in the i-th row and the j-th column. The pixel circuit20includes nine thin film transistors (hereinafter referred to as TFTs) Q1to Q9, and the liquid crystal capacitance23. The TFTs Q1, Q3, Q5, Q6, Q9are N-channel type TFTs, and the TFTs Q2, Q4, Q7, Q8are P-channel type TFTs. The liquid crystal capacitance23has a pixel electrode24and a common electrode25. Note that although the common electrode25is depicted for each pixel circuit20inFIGS. 2 and 3, the common electrode25is commonly provided to all of the pixel circuits20in reality.

A gate terminal of the TFT Q1is connected to the scanning line Gi. One conduction terminal (left-side terminal inFIG. 3) of the TFT Q1is connected to the data line Dj. The other conduction terminal of the TFT Q1and drain terminals of the TFTs Q4, Q5are connected to gate terminals of the TFTs Q2, Q3, Q6, Q7. The control signal SWij is a signal on a wiring connecting these terminals. Drain terminals of the TFTs Q2, Q3are connected to gate terminals of the TFTs Q4, Q5, Q8, Q9. The control signal SBij is a signal on a wiring connecting these terminals.

The high-level voltage VDD is applied to source terminals of the TFTs Q2, Q4. The low-level voltage VSS is applied to source terminals of the TFTs Q3, Q5. The white voltage Vw is applied to one conduction terminal (left-side terminal inFIG. 3) of the TFT Q6and one conduction terminal (right-side terminal inFIG. 3) of the TFT Q8. The black voltage Vb is applied to one conduction terminal (left-side terminal inFIG. 3) of the TFT Q7and one conduction terminal (right-side terminal inFIG. 3) of the TFT Q9. The other conduction terminals of the TFTs Q6to Q9are connected to the pixel electrode24of the liquid crystal capacitance23. The common electrode voltage Vcom is applied to the common electrode25of the liquid crystal capacitance23.

The TFT Q1functions as a write control transistor. The TFTs Q2to Q5function as a flip-flop circuit. When a voltage of the scanning line Gi is at a high level, the TFT Q1turns on, and a voltage of the data line Dj is input to the flip-flop circuit through the TFT Q1. With this, data is written to the flip-flop circuit. While the voltage of the scanning line Gi is at a low level, the flip-flop circuit retains the written data. The control signal SWij has a level corresponding to the data retained in the flip-flop circuit. The control signals SWij, SBij change complementarily (when one is at the high level, the other is at the low level). The flip-flop circuit including the TFTs Q2to Q5functions as a memory circuit configured to memorize the data input through the TFT Q1, and to output the control signals SWij, SBij that change complementarily in accordance with the memorized data.

A voltage of the pixel electrode24in the pixel circuit20in the i-th row and the j-th column is hereinafter referred to as VPij. The TFT Q6applies the white voltage Vw to the pixel electrode24according to the control signal SWij. The TFT Q7applies the black voltage Vb to the pixel electrode24according to the control signal SWij. The TFT Q8applies the white voltage Vw to the pixel electrode24according to the control signal SBij. The TFT Q9applies the black voltage Vb to the pixel electrode24according to the control signal SBij. When the control signal SWij is at the high level and the control signal SBij is at the low level, the TFTs Q6, Q8turn on, the TFTs Q7, Q9turn off, and the voltage VPij becomes equal to the white voltage Vw. When the control signal SWij is at the low level and the control signal SBij is at the high level, the TFTs Q6, Q8turn off, the TFTs Q7, Q9turn on, and the voltage VPij becomes equal to the black voltage Vb. The TFTs Q6to Q9function as the voltage selection circuit22that applies one of the white voltage Vw and the black voltage Vb to the pixel electrode24according to the control signals SWij, SBij.

FIG. 4is a diagram showing an example of changes of a display screen of the liquid crystal display device10. A pixel in the i-th row and the j-th column is hereinafter referred to as Pij. In the example shown inFIG. 4, in an initial state, colors of pixels P12, P21, P23, P32are white, and colors of other pixels are black. In a first frame period, the colors of the pixels P12, P21, P23, P32change to black, and the colors of the other pixels change to white. In a second frame period, the colors of the pixels P12, P21, P23, P32change to white, and colors of pixels P13, P22, P31change to black. In a third frame period, the colors of the pixels P13, P22, P31change to white.

FIG. 5is a timing chart of the liquid crystal display device10.FIG. 5describes changes of signals and voltages in the first to third frame periods when the display screen changes as shown inFIG. 4. As shown inFIG. 5, one frame period is divided into a write period and a retention period. In the retention period, all of the signals and the voltages do not change.

The gate clock GCK becomes the high level three times in one frame period. High-level periods of the gate clock GCK are hereinafter referred to as first to third selection periods in an order of appearance. Voltages of the scanning lines G1to G3become the high level in the first to third selection periods, respectively. Voltages of the data lines D1to D3become levels corresponding to the video signal VS in beginnings of the first to third selection periods. Note that there are a case where the voltages of the data lines D1to D3change from those in a previous selection period, and a case where the voltages of the data lines D1to D3do not change from those in the previous selection period.

The white voltage output circuit15outputs, as the white voltage Vw, a same voltage to all of the pixel circuits20. The white voltage Vw becomes the high level in odd-numbered frame periods, and becomes the low level in even-numbered frame periods. The white voltage output circuit15controls the white voltage Vw in a later-described manner in accordance with a timing when the voltage of the pixel electrode24changes.

The black voltage output circuit16outputs, as the black voltage Vb, a same voltage to all of the pixel circuits20. The black voltage Vb becomes the low level in the odd-numbered frame periods, and becomes the high level in the even-numbered frame periods. The black voltage output circuit16controls the black voltage Vb to have a constant level in the frame period. The common electrode drive circuit17controls the common electrode voltage Vcom to have a constant level in the frame period. The common electrode voltage Vcom becomes the low level in the odd-numbered frame periods, and becomes the high level in the even-numbered frame periods.

The voltages of the scanning lines G1to G3become the high level in the first to third selection periods, respectively, and the voltages of the data lines D1to D3become levels in accordance with the video signal VS in the beginnings of the first to third selection periods. Thus, in the beginnings of the first to third selection periods, the TFT Q1turns on, and the voltage of the data line Dj is input to the flip-flop circuit through the TFT Q1. Therefore, in the beginning of an i-th selection period, the control signal SWij becomes a level in accordance with the video signal VS, and the control signal SBij becomes a level which is opposite to that of the control signal SWij.

For example, in the beginning of the first selection period in the first frame period, the voltages of the data lines D1to D3become the high level, the low level, and the high level, respectively. Thus, in the beginning of a first write period in the first frame period, control signals SW11to SW13become the high level, the low level, and the high level, respectively, and control signals SB11to SB13(not shown) become the low level, the high level, and the low level, respectively.

The white voltage output circuit15controls the white voltage Vw to have a level that is more distant from the black voltage Vb than a normal level (final level that the white voltage Vw should have), in accordance with the timing when the voltage of the pixel electrode24changes. More specifically, a control period that is sufficiently short compared to the selection period is set in the beginning of each selection period. The white voltage output circuit15controls the white voltage Vw to have the level that is more distant from the black voltage Vb than the normal level, in an impulse manner in each control period.

Thus, in the odd-numbered frame periods when the black voltage Vb is at the low level, the white voltage Vw becomes higher than a normal high level in the impulse manner in the beginning of each selection period. In the even-numbered frame periods when the black voltage Vb is at the high level, the white voltage Vw becomes lower than a normal low level in the impulse manner in the beginning of each selection period.

Length of the control period, and a highest level and a lowest level of the white voltage Vw in the control period are determined so that later-described effects can be attained. For example, the highest level of the white voltage Vw in the control period is determined to have a level that is higher than the normal high level by about 10% of a difference between the white voltage Vw and the black voltage Vb. The lowest level of the white voltage Vw in the control period is determined to have a level that is lower than the normal low level by about 10% of the above-described difference.

FIG. 6is a detailed timing chart of the liquid crystal display device10.FIG. 7is a diagram continued fromFIG. 6.FIG. 6describes changes of the signals and the voltages in the first frame period, andFIG. 7describes the changes of the signals and the voltages in the second frame period. InFIGS. 6 and 7, VCij represents a voltage applied to the liquid crystal capacitance23in the pixel circuit20in the i-th row and the j-th column, Lij represents luminance (transparency) of the pixel Pij in the i-th row and the j-th column. Note that, in order to facilitate understanding of the drawings, a waveform of the white voltage Vw is depicted using a broken line overlapping on a waveform of the voltage VCij, and portions where the white voltage Vw changes in the impulse manner are depicted in an enlarged manner in an amplitude direction and a time direction.

As a liquid crystal display device according to a comparative example, there is considered a liquid crystal display device having the same configuration as the liquid crystal display device10, in which the white voltage Vw does not change in the impulse manner in the beginning of each selection period.FIG. 8is a detailed timing chart of the liquid crystal display device according to the comparative example.FIG. 8describes changes of the signals and the voltages in the same case asFIG. 6with respect to the liquid crystal display device according to the comparative example.

Referring toFIGS. 6 to 8, effects of the liquid crystal display device10according to the present embodiment will be described. InFIGS. 6 and 8, in the beginning of the first selection period in the first frame period, the voltage of the scanning line G1changes to the high level, and the voltage of the data line D1also changes to the high level. Thus, in the pixel circuit20in a first row and a first column, the control signal SW11changes to the high level, the control signal SB11changes to the low level, and a voltage VP11(not shown) of the pixel electrode24changes to the high level. The common electrode voltage Vcom is at the low level in the first frame period. Therefore, the voltage VC11applied to the liquid crystal capacitance23changes from the low level to the high level, and accordingly a color of the pixel P11changes from black to white. The liquid crystal display device10and the liquid crystal display device according to the comparative example are the same with respect to the points described so far.

In the liquid crystal display device according to the comparative example (FIG. 8), liquid crystal molecules positioned in a surrounding portion of the pixel P11are in a state of being difficult to move, because they are affected by electric field from the pixel electrodes of neighboring pixels and neighboring wirings. Thus, even if an electric field is applied between the pixel electrode and the common electrode of the pixel P11in the beginning of the first selection period in the first frame period, orientations of the liquid crystal molecules existing in the surrounding portion of the pixel P11do not change immediately, and an orientation abnormality occurs. Thus, luminance L11of the pixel P11changes slowly. Similar phenomena occur in other selection periods when the color of the pixel changes from black to white.

On the contrary, in the liquid crystal display device (FIGS. 6 and 7), the white voltage output circuit15controls the white voltage Vw to have the level that is distant from the black voltage Vb in the impulse manner, in accordance with the timing when the voltage of the pixel electrode24changes. For example, the white voltage Vw becomes higher than the normal high level in the impulse manner in the beginning of the first selection period in the first frame period. Thus, the voltage VC11applied to the liquid crystal capacitance23in the pixel circuit20in the first row and the first column becomes higher than the normal level in the impulse manner in the beginning of the first selection period in the first frame period. With this, even if the liquid crystal molecules existing in the surrounding portion of the pixel P11are in the state of being difficult to move, a trigger for the liquid crystal molecules included in the liquid crystal capacitance23to start to move can be provided. Therefore, the orientations of the liquid crystal molecules existing in the surrounding portion of the pixel P11can be changed quickly, and an afterimage caused by the orientation abnormality that occurs when a display image is switched can be prevented. Furthermore, by controlling the white voltage Vw in the impulse manner in accordance with the timing when the voltage of the pixel electrode24changes, the white voltage Vw having the normal level can be applied after the liquid crystal molecules start to move, and the color of the pixel P11can be controlled to be white. Similar effects can be attained in other selection periods when the color of the pixel changes from black to white.

As described above, the liquid crystal display device10according to the present embodiment is a reflective type liquid crystal display device performing the binary display, and includes the display section11including the scanning lines G1to Gm, the data lines D1to Dn, and the pixel circuits20, the scanning line drive circuit13that drives the scanning lines G1to Gm, the data line drive circuit14that drives the data lines D1to Dn, a first voltage output circuit (white voltage output circuit15) that outputs a first voltage (white voltage Vw), and a second voltage output circuit (black voltage output circuit16) that outputs a second voltage (black voltage Vb). The pixel circuit20includes the liquid crystal capacitance23having the pixel electrode24, and applies one of the first voltage and the second voltage to the pixel electrode24in accordance with the data written by driving the scanning line Gi and the data line Dj. The first voltage output circuit controls the first voltage to have a level that is more distant from the second voltage than the normal level (a level higher than the normal high level, or a level lower than the normal low level), in accordance with the timing when the voltage of the pixel electrode24changes.

According to the liquid crystal display device10according to the present embodiment, by controlling the first voltage to have the level that is more distant from the second voltage than the normal level, in accordance with the timing when the voltage of the pixel electrode24changes, a trigger for the liquid crystal molecules included in the liquid crystal capacitance23to start to move can be provided. Therefore, the orientations of the liquid crystal molecules existing in the surrounding portion of the pixel can be changed quickly, and the afterimage caused by the orientation abnormality that occurs when the display image is switched can be prevented.

The first voltage output circuit makes the first voltage change in the impulse manner in accordance with the above-described timing. Therefore, the first voltage having the normal level can be applied after the liquid crystal molecules start to move, and the color of the pixel can be controlled to be a color corresponding to the first voltage.

The second voltage output circuit controls the second voltage to have a constant level in the frame period. Therefore, the above-described effects can be attained without performing any special control with respect to the second voltage. The first voltage output circuit outputs, as the first voltage, a same voltage to all of the pixel circuits20, and controls the first voltage in accordance with all of the timings when the voltage of the pixel electrode24changes. Therefore, the above-described effects can be attained with a simple configuration.

The liquid crystal display device10further includes the common electrode drive circuit17that drives the common electrode25of the liquid crystal capacitance23, and the first voltage output circuit, the second voltage output circuit, and the common electrode drive circuit17invert a level of a voltage output from each circuit, for each frame period. Therefore, the above-described effects can be attained with respect to a liquid crystal display device performing frame inversion drive.

The pixel circuit20further includes a write control transistor (TFT Q1) having a control terminal (gate terminal) connected to the scanning line Gi, and one conduction terminal connected to the data line Dj, a memory circuit (flip-flop circuit) that memorizes the data input through the write control transistor and outputs the control signals SWij, SBij in accordance with the data, and the voltage selection circuit22that applies one of the first voltage and the second voltage to the pixel electrode24according to the control signals SWij, SBij. Therefore, the above-described effects can be attained with respect to a memory type liquid crystal display device.

The memory circuit is the flip-flop circuit that outputs, as the control signal, a first control signal (control signal SWij) and a second control signal (control signal SBij) that change complementarily, and the voltage selection circuit22includes a transistor (TFT Q6) that applies the first voltage to the pixel electrode24according to the first control signal, a transistor (TFT Q7) that applies the second voltage to the pixel electrode24according to the first control signal, a transistor (TFT Q8) that applies the first voltage to the pixel electrode24according to the second control signal, and a transistor (TFT Q9) that applies the second voltage to the pixel electrode24according to the second control signal. Therefore, the above-described effects can be attained with respect to a memory type liquid crystal display device including such a pixel circuit20.

Note that, it is assumed that in the liquid crystal display device according to the present embodiment, a timing when the voltage of the scanning line Gi becomes the high level and a timing when the voltage of the data line Dj becomes a level in accordance with the video signal VS are almost the same. In a case where the two timings are different, the voltage of the pixel electrode24changes according to a later timing. Therefore, in this case, it is enough for the white voltage output circuit15to make the white voltage Vw change in the impulse manner in accordance with the later timing.

Second Embodiment

A liquid crystal display device according to a second embodiment has the same configuration (FIGS. 1 to 3) as that of the liquid crystal display device10according to the first embodiment, and controls the white voltage in a manner different from that of the first embodiment. Differences from the first embodiment will be described below.

FIG. 9is a timing chart of the liquid crystal display device according to the present embodiment.FIG. 9describes changes of the signals and the voltages in the same case asFIG. 5with respect to the liquid crystal display device according to the present embodiment.FIG. 10is a detailed timing chart of the liquid crystal display device according to the present embodiment.FIG. 10describes changes of the signals and the voltages in the first frame period.

As shown inFIGS. 9 and 10, also in the liquid crystal display device according to the present embodiment, the white voltage output circuit15controls the white voltage Vw to have the level that is more distant from the black voltage Vb than the normal level in accordance with the timing when the voltage of the pixel electrode24changes. However, in the present embodiment, differently from the first embodiment, the white voltage output circuit15makes the white voltage Vw change in a rectangular pulse manner in accordance with the timing when the voltage of the pixel electrode24changes.

Thus, in the odd-numbered frame periods when the black voltage Vb is in the low level, the white voltage Vw becomes higher than the normal high level in the rectangular pulse manner in the beginning of each selection period. In the even-numbered frame periods when the black voltage Vb is in the high level, the white voltage Vw becomes lower than the normal low level in the rectangular pulse manner in the beginning of each selection period.

As described above, in the liquid crystal display device according to the present embodiment, the first voltage output circuit (white voltage output circuit15) makes the first voltage (white voltage Vw) change in the rectangular pulse manner in accordance with the timing when the voltage of the pixel electrode24changes. According to the liquid crystal display device according to the present embodiment, the same effects attained by the first embodiment can be attained.

Third Embodiment

A liquid crystal display device according to a third embodiment has the same configuration (FIGS. 1 to 3) as that of the liquid crystal display device10according to the first embodiment, and controls the black voltage in a manner similar to the white voltage. Differences from the first embodiment will be described below.

FIG. 11is a timing chart of the liquid crystal display device according to the present embodiment.FIG. 11describes changes of the signals and the voltage in the same case asFIG. 5with respect to the liquid crystal display device according to the present embodiment.

As shown inFIG. 11, also in the liquid crystal display device according to the present embodiment, the white voltage output circuit15controls the white voltage Vw to have the level that is more distant from the black voltage Vb than the normal level, in accordance with the timing when the voltage of the pixel electrode24changes. In addition, in the present embodiment, the black voltage output circuit16controls the black voltage Vb to have a level that is more distant from the white voltage Vw than a normal level (final level that the black voltage Vb should have), in accordance with the timing when the voltage of the pixel electrode24changes. The black voltage output circuit16makes the black voltage Vb change in the impulse manner in accordance with the timing when the voltage of the pixel electrode24changes.

Thus, in the odd-numbered frame periods when the black voltage Vb is in the low level, in the beginning of each selection period, the white voltage Vw becomes higher than the normal high level in the impulse manner, and the black voltage Vb becomes lower than the normal low level in the impulse manner. In the even-numbered frame periods when the black voltage Vb is in the high level, in the beginning of each selection period, the white voltage Vw becomes lower than the normal low level in the impulse manner, and the black voltage Vb becomes higher than the normal high level in the impulse manner.

As described above, in the liquid crystal display device according to the present embodiment, the second voltage output circuit (black voltage output circuit16) controls the second voltage (black voltage Vb) to have the level that is more distant from the first voltage (white voltage Vw) than the normal level (a level lower than the normal low level, or a level higher than the normal high level), in accordance with the timing when the voltage of the pixel electrode24changes. The second voltage output circuit makes the second voltage change in the impulse manner in accordance with the timing when the voltage of the pixel electrode24changes. According to the liquid crystal display device according to the present embodiment, in addition to the afterimage caused by the orientation abnormality that occurs when the color of the pixel is made to change from a color corresponding to the second voltage to the color corresponding to the first voltage, the afterimage caused by the orientation abnormality that occurs when the color of the pixel is made to change from the color corresponding to the first voltage to the color corresponding to the second voltage can be prevented.

As for the present embodiment, a following modification example can be configured. In the liquid crystal display device according to the modification example, in accordance with the timing when the voltage of the pixel electrode24changes, the white voltage output circuit15makes the white voltage Vw change in the rectangular pulse manner, and the black voltage output circuit16makes the black voltage Vb change in the rectangular pulse manner.FIG. 12is a timing chart of the liquid crystal display device according to the modification example. According to the liquid crystal display device according to the modification example, same effects attained by the liquid crystal display device according to the third embodiment can be attained.

Fourth Embodiment

A liquid crystal display device according to a fourth embodiment has a configuration in which the white voltage output circuit15is replaced with a later-described circuit in the liquid crystal display device10according to the first embodiment (FIG. 1), and controls the white voltage in a manner different from that of the first embodiment. Differences from the first embodiment will be described below.

FIG. 13is a diagram showing a detailed configuration of the liquid crystal display device according to the present embodiment. The liquid crystal display device shown inFIG. 13includes a white voltage output circuit35in place of the white voltage output circuit15. The pixel circuits20are classified into three groups corresponding to the scanning lines G1to G3. The pixel circuits20in the first row are classified as a first group, the pixel circuits20in a second row are classified as a second group, and the pixel circuits20in a third row are classified as a third group. The white voltage output circuit35outputs, as the white voltage, three voltages corresponding to the three groups. The white voltage output circuit35outputs a white voltage Vw1corresponding to the first group, outputs a white voltage Vw2corresponding to the second group, and outputs a white voltage Vw3corresponding to the third group. The white voltage output circuit35controls the white voltage corresponding to an i-th group to have a level that is more distant from the black voltage Vb than the normal level, in accordance with a timing when the voltage of the pixel electrode24in the pixel circuit20in the i-th group changes.

FIG. 14is a timing chart of the liquid crystal display device according to the present embodiment.FIG. 14describes changes of the signals and the voltages in the same case asFIG. 5with respect to the liquid crystal display device according to the present embodiment. In the liquid crystal display device according to the present embodiment, the voltage of the pixel electrode24in the pixel circuit20in the first row changes in the beginning of the first selection period, the voltage of the pixel electrode24in the pixel circuit20in the second row changes in the beginning of the second selection period, and the voltage of the pixel electrode24in the pixel circuit20in the third row changes in the beginning of the third selection period (not shown).

In the control period set in the beginning of the first selection period, the white voltage output circuit35controls the white voltage Vw1to have the level that is more distant from the black voltage Vb than the normal level in the impulse manner. In the control period set at the beginning the second selection period, the white voltage output circuit35controls the white voltage Vw2to have the level that is more distant from the black voltage Vb than the normal level in the impulse manner. In the control period set in the beginning of the third selection period, the white voltage output circuit35controls the white voltage Vw3to have the level that is more distant from the black voltage Vb than the normal level in the impulse manner.

Thus, in the odd-numbered frame periods when the black voltage Vb is in the low level, the white voltage Vw1becomes higher than the normal high level in the impulse manner in the beginning of the first selection period, the white voltage Vw2becomes higher than the normal high level in the impulse manner in the beginning of the second selection period, and the white voltage Vw3becomes higher than the normal high level in the impulse manner in the beginning of the third selection period. In the even-numbered frame periods when the black voltage Vb is in the high level, the white voltage Vw1becomes lower than the normal low level in the impulse manner in the beginning of the first selection period, the white voltage Vw2becomes lower than the normal low level in the impulse manner in the beginning of the second selection period, and the white voltage Vw3becomes lower than the normal low level in the impulse manner in the beginning of the third selection period.

As described above, in the liquid crystal display device according to the present embodiment, the pixel circuits20are classified into groups corresponding to the scanning lines G1to Gm, and the first voltage output circuit (white voltage output circuit35) outputs, as the first voltage (white voltage), voltages (white voltages Vw1, Vw2, Vw3) corresponding to the groups, and controls the first voltage that corresponds to the group, in accordance with a timing when the voltage of the pixel electrode24in the pixel circuit20in the group changes. According to the liquid crystal display device according to the present embodiment, effects similar to those attained by the first embodiment can be attained. In addition, since the first voltage output circuit outputs the voltages as the first voltage, wirings that propagate the first voltage can be divided, capacitance of the wirings can be reduced, and the wirings that propagate the first voltage can be driven easily.

As for the above-described liquid crystal display device according to each embodiment, a variety of modification examples can be configured. For example, by arbitrarily combining features of each embodiment unless contrary to their characteristics, a liquid crystal display device having features of a plurality of embodiments may be configured. In a liquid crystal display device according to a modification example of the fourth embodiment, the white voltage output circuit may make the white voltages Vw1to Vw3change in the rectangular pulse manner. In a liquid crystal display device according to a modification example of the first and second embodiments, the black voltage output circuit may make the black voltage Vb change in the impulse manner or in the rectangular pulse manner. In a liquid crystal display device according to a modification example of the fourth embodiment, the black voltage output circuit may output, as the black voltage, voltages corresponding to the groups. Furthermore, a liquid crystal display device according to a modification example may include a pixel circuit other than the pixel circuit20shown inFIG. 3. For example, a liquid crystal display device according to a modification example may include a pixel circuit obtained by removing the TFTs Q8, Q9from the pixel circuit20, in place of the pixel circuit20.

Although the present invention is described in detail in the above, the above description is exemplary in all of the aspects and is not restrictive. It is understood that various other changes and modification can be derived without going out of the present invention.