KR100369336B1 - LCD with energy recovery and method for driving the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having an energy recovery function capable of reducing power consumption by recovering electric charges already driven when driving a liquid crystal panel and using the same to drive the liquid crystal panel and a driving method thereof.

The present invention provides a liquid crystal panel comprising: a plurality of common electrodes driving a horizontal axis, a plurality of segment electrodes driving a vertical axis, and a plurality of liquid crystal capacitors by liquid crystal between the electrodes; Applying a common voltage for driving the common electrode of the liquid crystal panel, recovering the voltage used when driving one of the common electrodes of the plurality of common electrodes is driven before or next to the one common electrode A common voltage selection circuit for providing the common electrode; A segment voltage selection circuit applying a segment voltage for driving a segment electrode of the liquid crystal panel, recovering a voltage used when driving one segment electrode among the plurality of segment electrodes, and providing the segment voltage for driving the next segment electrode. It includes.

Description

Liquid crystal display device having an energy recovery function and a driving method thereof {LCD with energy recovery and method for driving the same}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof capable of reducing power consumption by recovering and reusing a charge driven from a common electrode or a segment electrode.

1 is a block diagram of a liquid crystal panel in a conventional liquid crystal display device. 1 illustrates a super twisted nematic (STN) liquid crystal panel. Referring to FIG. 1, the conventional STN liquid crystal panel 10 includes a plurality of common electrodes COM0-COM3 driving a horizontal axis; A plurality of segment electrodes SEG0-SEG3 for driving the vertical axis; And a plurality of liquid crystal capacitors (CLC) formed by the liquid crystal existing between the common electrode and the segment electrode. Each liquid crystal capacitor CLC is driven by one corresponding common electrode of the plurality of common electrodes COM0-COM3 and one corresponding segment electrode of the plurality of segment electrodes SEG0-SEG3.

2 is a block diagram of a conventional liquid crystal display device. Referring to FIG. 2, a voltage for driving the common voltage selection circuit 20 and a segment electrode for the liquid crystal panel 10 generating a voltage for driving the common electrode of the liquid crystal panel 10, the liquid crystal panel 10. And a segment voltage selection circuit 30 for generating.

As illustrated in FIG. 1, the liquid crystal panel 10 includes a plurality of common electrodes COM0-COM3, a plurality of segment electrodes SEG0-GSEG3, and a liquid crystal capacitor CLC constituting the unit cell UC.

The common voltage selection circuit 20 is configured such that four MOS transistors MC1-MC4 form a pair to drive one common electrode among the plurality of common electrodes COM0-COM3. For example, in the case of the first common electrode COM1, two PMOS transistors MC1 and MC2 to which the common voltages C01 and C02 are applied to the gates, respectively, and common voltages C03 and C04 to the gates, respectively. Two NMOS transistors MC3 and MC4 are applied to form a pair to drive the first common electrode COM1.

Like the common voltage selection circuit, the segment voltage selection circuit 30 is configured such that four MOS transistors MS1-MS4 form a pair to drive one segment electrode among the plurality of segment electrodes SEG0-SG3. do. For example, in the case of the first segment electrode SEG0, the segment voltages S03 and S04 are applied to the gate and the two PMOS transistors MS1 and MS2 to which the segment voltages S01 and S02 are respectively applied. Two pairs of NMOS transistors MS3 and MS4 are configured to drive the first segment electrode SEG0.

In this case, voltages applied to the four MOS transistors MC1-MC4 and MS1-MS4 of the common voltage selection circuit 20 and the segment voltage selection circuit 30, respectively, are V0, V1, V2, V3, and V4. Using GND, the voltage for each electrode is selectively interrupted and driven.

Accordingly, the STN liquid crystal panel 10 has a voltage corresponding to the voltages V0, V1, V4, and GND applied to the gates of the four MOS transistors MC1-MC4 of the common voltage selection circuit 20 to the corresponding common electrode. The voltage corresponding to the voltages V0, V2, V3, and GND applied to the gates of the four MOS transistors MS1 to MS4 of the segment voltage selection circuit 20 is applied to the corresponding segment electrodes, thereby providing a liquid crystal capacitor. The charge is charged, and the charged charge drives the liquid crystal between the common electrode and the segment electrode of the liquid crystal capacitor. At this time, four MOS transistors MC1-MC4 and MS1-MS4 are applied with V0, V1, V2, V3, V4, and GND (ground voltage) because the voltage values charged according to the characteristics of the liquid crystal are different. to be.

The operation of the liquid crystal display of FIG. 2 will now be described with reference to the operation waveform diagram of FIG. 3. When the pattern shown in FIG. 3A is displayed through the liquid crystal panel 10, the common voltage selection circuit 20 applies a common voltage having a different level from the other common electrodes to the corresponding common electrode in the same manner as described above. Select one common electrode among a plurality of common electrodes, and the segment voltage selection circuit 30 applies a segment voltage corresponding to valid data to the selected common electrode to drive the corresponding liquid crystal capacitor CLC. do. In this manner, a desired pattern is displayed on the liquid crystal panel.

At this time, the liquid crystal capacitor is driven with a different polarity between neighboring frames, for example, one frame and two frames, that is, one frame is driven by a common voltage or a segment voltage of positive polarity, and the next two frames are of negative polarity. Drive with common voltage or segment voltage. This is because, when driven with a voltage of either polarity, the liquid crystal is easily aged and shortened in life.

The control signal for converting polarity in each frame is the polarity signal POL shown in FIG. 3B. The polarity of the common voltage and the segment voltage applied to the common electrode and the segment electrode are alternately driven depending on the polarity signal. However, the voltage levels at the positive polarity and the negative polarity are the same.

Since the conventional liquid crystal display device as described above is mainly used in mobile applications, it is important to reduce power consumption to the minimum.

The present invention is to solve the problems of the prior art as described above, the liquid crystal display having an energy recovery function that can reduce the power consumption by recovering the electric charge already driven in the liquid crystal panel and using it for driving the liquid crystal panel again. An object thereof is to provide a device and a method of driving the same.

1 is a block diagram of a conventional liquid crystal panel,

2 is a configuration diagram of a liquid crystal display device having the liquid crystal panel of FIG. 1;

3 is an operation waveform diagram of the liquid crystal display of FIG. 2;

4 is a configuration diagram of a liquid crystal display device having an energy recovery function according to an embodiment of the present invention;

FIG. 5 illustrates an example of a parasitic diode for providing an energy recovery path in the liquid crystal display of FIG. 4;

6 is a view showing an example of an energy recovery method for a segment monk electrode in the liquid crystal display device of the present invention;

7 is a view showing another example of an energy recovery method in a segment electrode in the liquid crystal display device of the present invention;

8 is an operation waveform diagram at the time of energy recovery from a segment electrode in the liquid crystal display device of the present invention;

9 is a view showing an operating waveform when energy is recovered from a common electrode in the liquid crystal display device of the present invention;

* Description of the symbols for the main parts of the drawings *

100: STN liquid crystal panel 200: common voltage selection circuit

210: common energy recovery means 300: segment voltage selection circuit

310: segment energy recovery means

MC11, MC12, MS11, MS12: PMOS transistor

MC13, MC14, MS13, MS14: NMOS Transistor

SW21-SW23, SW31-SW33: Switch PD: Parasitic Diode

The present invention provides a liquid crystal panel comprising a plurality of common electrodes driving a horizontal axis, a plurality of segment electrodes driving a vertical axis, and a plurality of liquid crystal capacitors by liquid crystal between the electrodes; Applying a common voltage for driving the common electrode of the liquid crystal panel, recovering the voltage used when driving one of the common electrodes of the plurality of common electrodes is driven before or next to the one common electrode A common voltage selection circuit for providing the common electrode; A segment voltage selection circuit applying a segment voltage for driving a segment electrode of the liquid crystal panel, recovering a voltage used when driving one segment electrode among the plurality of segment electrodes, and providing the segment voltage for driving the next segment electrode. It provides a liquid crystal display device comprising a.

The common voltage selection circuit includes four MOS transistors for providing a driving voltage for driving each of the plurality of common electrodes; Energy recovery means for recovering the voltage used when driving the corresponding one common electrode to be used when driving the common electrode before or next to the corresponding one common electrode.

In the common voltage selection circuit, the energy recovery means is connected between two neighboring common electrodes of a plurality of common electrodes, and a driving voltage for driving a MOS transistor from the common voltage selection circuit to each common electrode is applied. In this case, the common electrode is opened, and a plurality of switches for shorting the two common electrodes when recovering the voltage used in driving the common electrode are included.

The segment voltage selection circuit includes four MOS transistors for inputting a plurality of power supply voltages having different levels to provide driving voltages for driving each of the plurality of segment electrodes; Energy recovery means for recovering the driving voltage used when driving the segment electrode to be used when driving the segment electrode of the next frame.

A parasitic diode or a PN diode formed in the MOS transistor is connected between the source and the drain of the four MOS transistors of the segment voltage selection circuit.

In the segment voltage selection circuit, the energy recovery means applies the driving voltage to the four MOS transistors through the first port when driving the segment electrode, and through the second port when recovering the voltage used during the driving. A plurality of switches for applying the used voltage; It is connected to the second port of the switch is provided with an energy recovery capacitor for charging the used voltage.

The recovered voltage is used as the driving voltage of the largest level among the voltages applied to each segment, and the recovered voltage is obtained through a diode formed in the MOS transistor to which the driving voltage of the largest level is applied. It is applied to the capacitor to be charged. In this case, the diode and the anode is connected between the source and the drain, respectively, so that when the recovered voltage is greater than the potential of the capacitor is applied to the capacitor, if small, a reverse vice is formed to block.

The voltage recovered through the capacitor is applied to the segment electrode through the MOS transistor to which the driving voltage of the highest level is applied among the four MOS transistors, thereby precharging, and the recovered voltage is smaller than the potential of the segment. The diode is reverse biased to prevent the diode from being applied to the segment electrode to prevent the loss of the recovered voltage.

In addition, the present invention applies a driving voltage to a corresponding one of the plurality of common electrodes to drive the common electrode, and then to drive each segment electrode by applying different levels of driving voltage to the plurality of segment electrodes. A method of driving a liquid crystal display device, the method comprising driving the corresponding common electrode and recovering a driving voltage to precharge the common electrode before or after the corresponding common electrode and drive the segment driving. A method of driving a liquid crystal display device for recovering a next driving voltage and precharging the segment electrode is provided.

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings in order to describe the present invention in more detail.

4 is a block diagram of a liquid crystal display device according to an exemplary embodiment of the present invention. 4, a liquid crystal display device according to an exemplary embodiment of the present invention includes an STN liquid crystal panel 100 and common energy recovery means 210 for energy recovery from a common electrode of the liquid crystal panel 100. A segment voltage selection circuit 300 having a common voltage selection circuit 200 and segment energy recovery means 310 for energy recovery from the segment electrode of the liquid crystal panel 100 is provided.

The liquid crystal panel 100 is an STN liquid crystal panel and its configuration is the same as that of FIG. 1. The common voltage selection circuit 200 includes two PMOS transistors MC11 and MC12 to which the common voltages C1 and C2 are applied to the gates, and two NMOS transistors to which the common voltages C3 and C4 are respectively applied to the gates. Four MOS transistors of MC13 and MC14 form one set to provide a common voltage according to the power supply voltages V0, V1, V4, and GND to drive the corresponding common electrodes COM0-COM3.

In addition, the common voltage selection circuit 200 includes a common energy recovery means 210 for energy recovery at a common voltage of the liquid crystal panel 100, and the common energy recovery means 210 includes the plurality of common electrodes ( A plurality of switches SW21 to SW23 are configured to short or open common electrodes adjacent to each other among COM0-COM3. That is, in the common energy recovery means 210, the switches SW21 to SW23 are connected between common electrodes adjacent to each other among the plurality of common electrodes COM0-COM3.

The segment voltage selection circuit 300 includes two PMOS transistors MS11 and MS12 to which the common voltages S1 and S2 are applied to the gate, and two NMOS transistors to which the common voltages S3 and S4 are respectively applied to the gate. Four MOS transistors of the MS13 and the MS14 form one set to provide segment voltages corresponding to the power supply voltages V0, V2, V3, and GND to drive the corresponding segment electrodes SEG0-SEG3.

In addition, the segment energy recovery means 310 is composed of a switch (SW31-SW33) for controlling the power supply voltages (V0, V2, V3) and the energy recovery capacitors (Cst1, Cst2). That is, in the segment energy recovery means 310, the switches SW31 to SW33 transfer the respective power supply voltages V0, V2 and V3 to each segment electrode through the first port a when driving the segment electrodes. The second port (b) is connected to the charging capacitors Cst1 and Cst2 to transfer the recovered energy. The energy recovery capacitors Cst1 and Cst2 have a potential greater than that of the capacitors Cst1 and Cst2 among the potentials of the respective segment electrodes after driving the segment electrodes, and is charged through the b ports of the switches SW31 to SW33. Then, the charged charge (recovered energy) is again applied to the power terminal of each segment through port b of the switches SW31 to SW33.

FIG. 5 illustrates an example of a parasitic diode PD formed in four MOS transistors MS11-MS14 for driving each segment electrode SEG0-SEG3 in the segment voltage selection circuit 300 of FIG. will be.

The parasitic diode PD has a structure in which a cathode and an anode are connected to the source and the drain of the MOS transistor, respectively, and has a potential larger than that of the capacitors Cst1 and Cst2 among the potentials of the respective segment electrodes after driving the respective segment electrodes. The potential of the segment is transferred to the capacitor through the parasitic diode PD of one of the four MOS transistors, where a potential smaller than the capacitors Cst1 and Cst2 of each of the segment electrodes is a parasitic diode PD. Since a reverse bias is formed in () and is not transmitted to the segment electrode, no reverse current flow occurs.

In addition, when the potential of the segment electrode is smaller than the recovered energy after the energy recovery, the parasitic diode PD also has a reverse vice structure, so that the energy recovered in the capacitor does not occur. Therefore, it becomes possible to recover energy more efficiently than using another separate switch.

In the embodiment of the present invention, a parasitic diode typically formed in a MOS transistor is used for energy recovery of a segment, but as another embodiment, a PN diode separate from the MOS transistor may be formed to be connected to the MOS transistor. have.

6 and 7 illustrate an example of a liquid crystal display device in a segment energy recovery operation in the segment electrode, and the segment energy recovery operation in FIG. 6 drives the levels of the power supply voltages V0 and V2 in FIG. 3B. FIG. 7 illustrates a configuration for the energy recovery operation when driving the levels of the power supply voltages V3 and VSS (GND) of FIG. 3B.

The method of recovering the segment energy of the present invention drives the corresponding one segment electrode of the STN liquid crystal panel, and then recovers the electric charges used to drive the segment electrode of the next frame. To reduce it.

FIG. 8 shows an operational waveform diagram of the liquid crystal display element during the recovery operation of the segment energy in FIG. 6, wherein the upper waveform diagram shows the drive waveform during the recovery operation of the segment energy at the level of the power supply voltages V0 and V2. The lower waveform diagram shows an enlarged view of the upper driving waveform diagram.

Referring to FIG. 8, when looking at the first energy recovery operation duty, the first segment electrode SEG0 is the power supply voltage V2 and the second segment electrode SEG1 is the power supply voltage V0. In operation, the switch SW1 moves to the port b in FIG. 6 during the energy recovery operation.

Therefore, in the energy recovery means 310 of the segment voltage selection circuit 3000, all of the power supply terminals V0 are connected to the capacitor Cst1, and since the potential of the third segment electrode SEG2 is the highest, When only the potential of the three-segment electrode SEG2 moves to the capacitor Cst1, and the potentials of the remaining first and second segment electrodes SEG0 and SEG1 are all V2, the potential of the capacitor Cst1 is higher than V2. There is no reverse bias applied to the parasitic diode PD as shown in Fig. 5. Therefore, only the potential higher than the capacitor Cst1 moves to the capacitor Cst1, and the potential of the capacitor Cst1 is higher than the potential of the capacitor Cst1. In the low case, no reverse current flows.

The movement path for energy recovery is a PMOS transistor MS11 connected to the power supply terminal V0 of the segment voltage selection circuit 300 and moves through the parasitic diode PD path of FIG. 5 formed in the PMOS transistor MS11. Done. In this way, the energy recovered through the capacitor Cst1, that is, the charge accumulated in the capacitor Cst1, is used for the precharge before the next drive (drive of d2 in FIG. 8).

The movement path for precharge of the energy recovered through the segment energy recovery means 310 is from the capacitor Cst1 to the b port of the switch SW1, the power supply voltage V0 terminal of each segment electrode, and the PMOS transistor of each segment electrode. Is passed to (MS11). When the precharge operation is completed through the switching of the PMOS transistor MS11, the switch SW1 is connected to the a port again, so that each segment electrode is driven by a power supply in a conventional manner.

As described above, after driving each segment electrode, the energy used to drive each segment electrode is charged and recovered through a capacitor, and the recovered energy is used for driving the next segment to enable energy recovery and reuse. do.

In the above energy recovery operation, when the energy of the segment is less than the amount charged in the capacitors Cst1 and Cst2, the parasitic diode PD formed in the MOS transistor of each segment electrode is reverse biased to the capacitors Cst1 and Cst2. No loss of charged charge occurs.

FIG. 7 illustrates a case in which the driving voltages of the segment electrodes are V3 and VSS, and the energy recovery path is formed in the parasitic diode PD and the switch SW2 of FIG. 5 formed in the PMOS transistor MS12 connected to the power supply voltage V2. The energy recovered through the recovery port is stored in the capacitor Cst2, and then the power supply voltage V3 terminal of each segment electrode through the b port of the switch SW3 and the NMOS transistor MS13. Precharged through, and after the precharge is connected to a port of the switch (SW3) to supply power to each segment electrode.

FIG. 9 shows a waveform diagram in the energy recovery operation of the common electrode, wherein the upper waveform diagram shows a driving waveform diagram during the energy recovery operation of the common electrode, and the lower waveform diagram shows a driving waveform diagram of the upper waveform diagram. It is enlarged.

In the common electrode energy recovery waveform, the first common electrode COM0 is driven to VSS in the d1 section and to V1 in the d2 section. The second common electrode COM1 adjacent to the first common electrode COM0 is driven opposite to the first common electrode COM0.

The energy recovery at the common electrode shorts a corresponding one common electrode among the plurality of common electrodes, for example, the second common electrode COM1 and the adjacent third common electrode COM2 to be driven next to the common electrode COM1. Energy is recovered, and the recovered energy precharges the previously driven first common electrode COM0 and the common electrode COM2 to be driven next to the corresponding common electrode C1. do. During the recovery of the energy of the common electrode, all four MOS transistors MC11 to MC14 for driving each common electrode remain off.

After the energy recovery operation as described above, the common electrode is supplied from the common voltage selection circuit 200 to each common electrode in a conventional manner to drive the common electrode. Therefore, the energy used in the precharge is charged to the previous or next common electrode, thereby enabling energy recovery and use.

According to the liquid crystal display of the present invention as described above, the power source used when driving the segment electrode or the common electrode is recovered and used for driving the segment electrode of the next frame, or the common electrode sphere of the next common electrode or the next frame. By using at the same time, power consumption can be reduced.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (16)

A liquid crystal panel having a plurality of common electrodes driving a horizontal axis, a plurality of segment electrodes driving a vertical axis, and a plurality of liquid crystal capacitors by liquid crystal between the electrodes; Applying a common voltage for driving the common electrode of the liquid crystal panel, recovering the voltage used when driving one of the common electrodes of the plurality of common electrodes is driven before or next to the one common electrode A common voltage selection circuit for providing the common electrode; A segment voltage selection circuit applying a segment voltage for driving a segment electrode of the liquid crystal panel, recovering a voltage used when driving one segment electrode among the plurality of segment electrodes, and providing the segment voltage for driving the next segment electrode. Liquid crystal display device comprising a. The method of claim 1, wherein the common voltage selection circuit Four MOS transistors for providing a driving voltage for driving each of the plurality of common electrodes; And an energy recovery means for recovering the voltage used when driving the corresponding common electrode and using the same voltage when driving the common electrode before or after the corresponding common electrode. The method of claim 2, wherein the energy recovery means is connected between two neighboring common electrodes of a plurality of common electrodes, and a driving voltage for driving a MOS transistor from the common voltage selection circuit to each common electrode is applied. And a plurality of switches for shorting the two common electrodes when the common electrode is opened and the voltage used to drive the common electrode is recovered. 4. The liquid crystal display device according to claim 3, wherein each common electrode driving MOS transistor is turned off when the voltage used in driving the common electrode is recovered. The circuit of claim 1, wherein the segment voltage selection circuit comprises: Four MOS transistors for inputting a plurality of power supply voltages having different levels to provide driving voltages for driving each of the plurality of segment electrodes; And an energy recovery means for recovering the driving voltage used during the driving of the segment electrode to be used for driving the next segment electrode. 6. The liquid crystal display device according to claim 5, wherein the segment voltage selection circuit further comprises a parasitic diode or a separate PN diode formed between the sources and the drains of the four MOS transistors. 7. The energy recovery means according to claim 6, wherein in said segment voltage selection circuit, A plurality of switches for applying a driving voltage to four MOS transistors through a first port when driving the segment electrode, and applying the used voltage through a second port when recovering the voltage used for driving; And an energy recovery capacitor connected to the second port of the switch to charge the used voltage. 8. The liquid crystal display device according to claim 7, wherein the recovered voltage is a drive voltage having the highest level among the voltages applied to each segment. The liquid crystal display device of claim 8, wherein the recovered voltage is applied to the capacitor through a diode connected to a MOS transistor to which a driving voltage of the highest level is applied among four MOS transistors. 10. The method of claim 9, wherein the cathode and the anode is connected between the source and the drain, respectively, the diode is applied to the capacitor only when the recovered voltage is greater than the potential of the capacitor, if the reverse vice is formed and blocked Liquid crystal display device characterized in that. The liquid crystal display device of claim 7, wherein the voltage recovered through the capacitor is precharged by being applied to the segment electrode through a MOS transistor to which a driving voltage of the highest level is applied among four MOS transistors. . 12. The liquid crystal of claim 11, wherein when the voltage recovered through the capacitor is smaller than the potential of the segment, the diode is reverse biased to prevent the diode from being applied to the segment electrode, thereby preventing the loss of the recovered voltage. Display element. Driving the common electrode by applying a driving voltage to one common electrode among the plurality of common electrodes, and then driving each segment electrode by applying different driving voltages to the plurality of segment electrodes. In the method, Driving the corresponding common electrode and then recovering a driving voltage to precharge the common electrode before or after the corresponding common electrode; And driving the segment driving to recover the driving voltage to precharge the segment electrode. The liquid crystal display device of claim 13, wherein when the driving voltage used to drive the common electrode is recovered, the corresponding common electrode is shorted and recovered with the next common electrode adjacent to each other. Way. The method of claim 14, wherein the driving voltage applied to the common electrode is cut off when the driving voltage used to drive the common electrode is recovered. The liquid crystal display device of claim 13, wherein the driving voltage of the largest level among the driving voltages applied to the segment electrodes is used when the driving voltages used to drive the segment electrodes are recovered. Driving method.