CN1310082C - Thermomechanical approach for optically compensated bend-mode liquid crystal displays - Google Patents

Abstract

The invention is a thermal method of Optically Compensated Bend (OCB) mode LCD, wherein the LCD has pixel unit array, and each pixel unit includes a thin film transistor, the thin film transistor can determine whether to conduct according to the grid signal of the grid terminal, make the data signal of the source transmit to the pixel electrode, and have a common electrode on the other side relative to the pixel electrode, and a liquid crystal layer is sandwiched between pixel electrode and common electrode, the method includes the following steps at least. First, the source of the thin film transistor is floated. Then, a gate signal is applied to the gate electrode, whereby the voltage level of the pixel electrode is coupled to a level similar to that of the gate signal, thereby accelerating the transition of the liquid crystal molecules in the liquid crystal layer from the splay state to the bend state.

Description

Thermomechanical approach for optically compensated bend-mode liquid crystal displays

technical field

The present invention is related to a driving mode of an optically compensated bend (OCB) mode liquid crystal display (OCB mode LCD), in particular, a method of coupling the gate voltage level of a thin film transistor to a pixel electrode (pixel ) method to accelerate the conversion of liquid crystal molecules from a splay state to a bend state.

Background technique

With the rapid progress of thin-film transistor manufacturing technology, liquid crystal displays are widely used in personal digital assistants (PDAs), notebook computers, digital cameras, camcorders, mobile phones, etc. In various electronic products such as telephones. Coupled with the industry's active investment in research and development and the adoption of large-scale production equipment, the quality of liquid crystal displays has been continuously improved, and the price has continued to decline, which has also rapidly expanded the application fields of liquid crystal displays.

In order to further increase the reaction rate of the liquid crystal layer and widen the viewing angle, in the production of the current liquid crystal display, three main improvement methods are designed based on the material properties of the liquid crystal molecules. These three improvement methods include: (1) adopting vertical alignment (Vertical Alignment; VA) liquid crystal mode; (2) developing low-viscosity liquid crystal molecules; and (3) adopting optical compensation bending (OCB) mode. Among them, the way of vertical alignment is to change the surface shape of the alignment film, so that the liquid crystal molecules are arranged and distributed along the surface of the alignment film. In this way, when a voltage is applied to the pixel electrode (pixel electrode), the liquid crystal molecules can rotate rapidly. presents a vertical arrangement. As for the way to develop low-viscosity liquid crystal materials, it focuses on the proportional relationship between the liquid crystal reaction time and the viscosity of liquid crystal molecules. Therefore, when the viscosity of liquid crystal molecules decreases, the reaction time will be shortened.

As for the liquid crystal display using the OCB mode, the liquid crystal molecules distributed on the surface of the upper and lower glass substrates are aligned in parallel, but the liquid crystal molecules in the inner layer are not twisted, but are arranged in a bend in a plane. The birefringence of the light is due to the addition of a biaxial retardation film (Biaxial Retardation Film), which can compensate the phase difference of each axis and overcome the influence of the angle of view being affected by the change of optical characteristics caused by the tilt of the liquid crystal molecules, so it can provide the effect of wide viewing angle . In addition, since the liquid crystal molecules in the OCB mode are only arranged in a curved manner, unlike the liquid crystal molecules in the TN mode, it is not necessary to overcome the backflow (Backflow) hysteresis that changes the twisted arrangement, so the liquid crystal display using the OCB mode can reduce the reaction rate. To 1 ~ 10ms, much shorter than the response time of the traditional TN liquid crystal mode (about 50ms).

It is worth noting that although the OCB mode liquid crystal display has the above-mentioned advantages, there are still many defects in application. For example, the existing OCB mode liquid crystal display often needs a long warm-up time to make the liquid crystal molecules in the liquid crystal layer change from the splay state to the bend state for actual operation. )state. In order to accelerate the transition of the liquid crystal molecules from the slanted state to the curved state, in the current design of the OCB mode liquid crystal display, a high voltage is often applied to both ends of the liquid crystal layer to accelerate the rotation of the liquid crystal molecules.

Please refer to Figure 1, which shows the circuit structure of a unit pixel in a liquid crystal display. The unit pixel is mainly used as a switch by a thin film transistor 10 . Wherein, the gate of the thin film transistor 10 is connected to the gate driver chip (Gate Driver) 13 via a scanning line 12, and the source is connected to the source electrode driver chip (Source Driver) 15 via a data line 14. The drain is connected to the storage capacitor C _st and the pixel electrode (pixel electrode) 16 respectively. On the other side of the pixel electrode 16, a common electrode (common electrode) 17 is provided. A liquid crystal layer 18 is just filled and sandwiched between the pixel electrode 16 and the common electrode 17 . When the scan signal (Vg) output by the gate drive chip 13 turns on the thin film transistor 10, the data signal (V _data ) from the source drive chip 15 can be transmitted to the pixel electrode 16 through the drain terminal, and communicate with The common electrode 17 generates a cross voltage to make the liquid crystal layer 18 generate the desired image.

In order to apply a high voltage to the pixel electrode 16 to accelerate the rotation of the liquid crystal molecules in the OCB mode, in the existing liquid crystal display, the design of the source driver chip 15 is often changed so that it has the ability to output a high voltage (for example, by 5 Volts are increased to 15 volts); or the design of the common electrode 17 is changed to reduce its voltage level (for example, from 6 volts to -16 volts), so that between the pixel electrode 16 and the common electrode 17, a Greater cross-pressure. However, in this way, it may be necessary to change the high-voltage process specification of the driver chip, or change the pattern design of the entire pixel, which will increase the overall cost and design difficulty.

Contents of the invention

The present invention discloses a thermomechanical method of an optically compensated bend (OCB) mode liquid crystal display. By coupling the level of the gate voltage of a thin film transistor to a pixel electrode (pixel), the liquid crystal molecules can be accelerated from splay ) state transitions to the bend state.

The invention discloses a thermomechanical method for an optically compensated bend (OCB) mode liquid crystal display, wherein the liquid crystal display has an array of pixel units, and each of the pixel units includes a thin-film transistor, and the thin-film transistor can be connected according to the gate signal at the gate terminal. The high and low potentials determine whether it is turned on or not, so that the data signal can be transmitted to the pixel electrode through the source electrode and the drain electrode. There is a common electrode on the other side of the pixel electrode, and a liquid crystal layer is sandwiched fit between the pixel electrode and the common electrode. The thermomechanical method provided by the present invention can be divided into two sections. In the previous warm-up period, the source of the thin film transistor is floated, and at the same time, a high-potential gate signal is continuously applied to the gate, so that the voltage level of the pixel electrode is coupled to the high level of the gate signal, which can accelerate the liquid crystal layer. The liquid crystal molecules switch from the slanted state to the curved state. As for, in the later warm-up time, the data signal supply of the source is resumed, and at the same time, the gate signal of high potential is continuously applied to the gate, and the data signal is input to the pixel electrode through the source and drain of the thin film transistor.

In addition, the present invention also provides another two-stage warm-up method. In the first warm-up period, the source of the thin film transistor is floated, and at the same time, a high-potential gate signal is continuously applied to the gate to make the voltage of the pixel electrode The level will be coupled to the high level which is similar to the gate signal, and can accelerate the transition of the liquid crystal molecules in the liquid crystal layer from the slanted state to the curved state. As for, in the later warm-up time, the data signal supply of the source is resumed, and at the same time, the periodic pulse of the gate signal is applied to the gate to turn on the thin film transistor, and the data signal is input to the pixel through the source and drain. electrode.

In addition, the present invention also provides another warm-up method. During the warm-up time, the source electrodes of the floating thin film transistors are floated, and the gates are sequentially supplied with pixel electrode scan signals (Vg) in a general scan mode, so that The voltage level of the pixel electrode will be coupled to the high level of the gate signal, which can accelerate the transition of the liquid crystal molecules in the liquid crystal layer from the slanted state to the curved state.

Description of drawings

Fig. 1 has shown the circuit structure of the unit pixel in the liquid crystal display at present;

Fig. 2 shows the situation that the source of the thin film transistor is in a floating state in the present invention, so that the high-level gate signal can be coupled to the pixel electrode through the coupling capacitance between the gate and the drain;

Fig. 3 shows the situation that the present invention controls the chip to output synchronous signal and data signal in time sequence, and controls the situation of the gate driver chip and the source driver chip;

Fig. 4 shows the signal waveforms output by the source driver chip and the gate driver chip in the first embodiment of the present invention;

5 shows signal waveforms output by the source driver chip and the gate driver chip in the second embodiment of the present invention;

FIG. 6 shows signal waveforms output by the source driver chip and the gate driver chip in the third embodiment of the present invention;

7 shows signal waveforms output by the source driver chip and the gate driver chip in the fourth embodiment of the present invention;

FIG. 8 shows signal waveforms output by the source driver chip and the gate driver chip in the fifth embodiment of the present invention.

Symbol Description:

TFT ~ 10

Scanline ~ 12

Gate driver chip ~ 13

Data line ~ 14

Source driver chip ~ 15

Pixel electrode ~ 16

Common electrode ~ 17

Liquid crystal layer ~ 18

Timing control chip ~ 20

Detailed ways

The present invention provides a thermomechanical method for an optically compensated bend (OCB) mode liquid crystal display. The liquid crystal display has an array of pixel units, and each pixel unit includes a thin film transistor, which can determine whether to conduct according to the potential of the gate signal, so that the data signal on the data line can pass through the source of the transistor. The electrode and the drain are transmitted to the pixel electrode. By floating the source of the thin film transistor, the voltage level of the pixel electrode can be coupled to the level of the gate signal through the gate-drain coupling capacitance (C _gd ). In this way, when the gate signal has a high potential, the high voltage level coupled to the pixel electrode can accelerate the transition of the liquid crystal molecules from the slanted state to the curved state. A detailed description of the present invention is as follows.

Please refer to Fig. 1, as mentioned above, take the circuit structure of the unit pixel in the current liquid crystal display as an example, the gate of the thin film transistor 10 is connected to the gate driver chip (GateDriver) 13 through the scan line 12, and the source is connected to the gate driver chip (GateDriver) 13 through the data The line 14 is connected to a source driver chip (SourceDriver) 15, and the drain is connected to an auxiliary capacitor C _st and a pixel electrode (pixel electrode) 16, respectively. Taking the NMOS transistor in the figure as an example, when the gate signal (Vg) output by the gate driver chip 13 has a high level, the thin film transistor 10 can be turned on, so that the data signal (V _data ) output by the source driver chip 15 , applied to the pixel electrode 16 through the source and drain, so that the liquid crystal layer 18 produces the desired image.

It is worth noting that the level of the above-mentioned data signal (V _data ) is often only a few volts (~5 volts), so when applied to the pixel electrode 16, the liquid crystal molecules in the liquid crystal layer 18 cannot be rapidly switched. to the working state. In comparison, the gate signal (Vg) output by the gate driver chip 13 is generally between -5 and 20 volts, and the high potential gate signal (V _gh ) is about ten volts level (~15 volts). Therefore, by coupling the high potential (V _gh ) of the gate signal to the pixel electrode 16, the transition of the liquid crystal molecules from the slanted state to the curved state can be accelerated, thereby shortening the heating time of the entire liquid crystal display.

Please refer to Fig. 2, in order to speed up the heat-up speed of the optically compensated bending (OCB) mode liquid crystal display, in the heat-up method of the present invention, be to make the source electrode of thin film transistor be in floating (floating) state first, to cut off the data signal (V _data ) supply. Next, a high potential gate signal (V _gh ) is applied to the gate. At this time, since the level of the gate signal (V _gh ) will be coupled to the pixel electrode 16 through the gate-drain coupling capacitance (C _gd ), the voltage level on the pixel electrode 16 will be Approximate to the level of the gate signal (V _gh ). For example, when the gate signal (V _gh ) is 15 volts, the voltage coupled to the pixel electrode 16 has a level of approximately 13.6 volts. In this way, the voltage difference across the pixel electrode 16 and the common electrode 17 (˜0 volts) can be as high as 13.6 volts, which can effectively accelerate the transition of the liquid crystal molecules in the liquid crystal layer 18 from the slanted state to the curved state.

It should be pointed out that when using the thermal engine method of the present invention, it is not necessary to increase the high-pressure process of the driver chip, but can be achieved by using the existing gate driver chip 13 and source driver chip 15 . Please refer to Fig. 3, because in current liquid crystal display design, drive chips 13 and 15 all operate by a timing control chip (ASIC IC), so when using the heat engine method of the present invention, only need to revise the timing control chip 20 Just control the signal. For example, by modifying the synchronous signal and data signal output by the timing control chip 20 , the data output of the source driver chip 15 can be controlled to be in a floating state, while the gate signal of the gate driver chip 13 can be maintained at a high potential.

Please refer to FIG. 4 , which shows signal waveforms output by the source driver chip 15 and the gate driver chip 13 in the first embodiment of the present invention. Wherein, the source driver chip 15 has an LD pin. When the output LD signal has an "ON" level, it means that the source driver chip 15 can latch the data signal sent to the pixel electrode (latch data to pixel). Therefore, when the warm-up program is started, the data signal can be latched by outputting the LD signal, so that the data signal output terminal of the source driver chip 15 (whether it is an odd-numbered row or an even-numbered row) generates high impedance and presents a floating state. set state.

On the other hand, there is an Xon pin on the gate driving chip 13, which can simultaneously control the gates of all thin film transistors to be in a high potential state. When the Xon signal is “OFF”, all gate signals are maintained at the high potential V _gh . As shown in the figure, during the entire warm-up time, the Xon signal is kept in the "OFF" state, so that the gate signal on each scan line (X1, X2, ... X5) is always kept at a high level The state of _Vgh . At this time, since the output of the data signal (V _data ) of the source driver chip 15 is in a floating state, for the thin film transistor 10 , the source for transmitting the data signal is also in a high-impedance floating state. In this way, the voltage level of the pixel electrode 16 will couple the gate signal (V _gh ) corresponding to the high potential through the gate-drain coupling capacitance C _gd , and accelerate the liquid crystal molecules in the liquid crystal layer 18 The conversion (transition).

Please refer to Figure 5. In order to further improve the warm-up effect of the liquid crystal display, in the second embodiment of the present invention, the entire warm-up time can be divided into the front section and the back section. In the front section of the warm-up program, the LD signal is continuously maintained at " ON” level, and latch the data signal transmitted to the pixel electrode, so that the data signal output terminal of the source driver chip 15 (including the odd row and the even row) presents a floating state. At the same time, keep the Xon signal of the gate driver chip 13 at “OFF”, and keep the gate signals on all the scan lines (X1, X2, . . . X5) at the high potential V _gh .

As for, in the back-stage heat-up program, the gate drive chip 13 continues to maintain the Xon signal at

In the "OFF" state, the high-level gate signal V _gh is continuously output. It is worth noting that, in the part of the source driver chip 15, the LD signal can be restored to the normal periodic switching. At this time, the data output terminal will also return to the normal data signal supply from the high-impedance floating state. As shown in the figure, after entering the later warm-up time, the data output terminal will output positive or negative data signals according to the difference between odd-numbered lines or even-numbered lines.

Please refer to Fig. 6. In the third embodiment of the present invention, the whole warm-up time is also divided into the front section and the back section. The data signal output terminals (including odd and even rows) of the pole driver chip 15 are in a high-impedance floating state. At the same time, keep the Xon signal of the gate driver chip 13 at “OFF”, and keep the gate signals on all the scan lines (X1, X2, . . . X5) at the high potential V _gh .

After entering the later warm-up program, the gate driver chip 13 controls the Xon signal to the "ON" state, at this time, the gate signals on all scan lines (X1, X2, ... X5) will be at a low level (V _gl ), and according to the periodic fluctuation of the timing reference signal (CPV), output the gate signal V _gh pulse to each scan line (X1, X2, ... X5) one by one. That is, the normal line-by-line scanning mode of the gate driver chip 13 is restored, and the conduction or non-conduction of the thin film transistors on each scanning line is controlled. Similarly, in the part of the source driver chip 15, the normal LD signal cycle can also be restored, so that the data output terminal will also be restored to the normal data signal supply from the high-impedance floating state, and according to the odd-numbered row or the even-numbered row The difference, respectively output positive or negative data signal.

It should be pointed out that, in addition to the above-mentioned method of continuously applying a high potential gate signal (V _gh ), a gate signal (V _gh /V _gl ) supply method of rapidly switching between high and low potentials can also be used to drive liquid crystal molecules to switch. Referring to FIG. 7 , in the fourth embodiment of the present invention, the data signal output terminals (odd and even rows) of the source driver chip 15 are still in a high impedance and floating state during the whole warm-up period. As for the gate signal output by the gate driver chip 13 , it switches back and forth between high and low potentials (V _gh /V _gl ) to form a specific periodic signal. In this case, the signal potential coupled to the pixel electrode will also switch back and forth between high and low levels, forcing the liquid crystal molecules to switch from a slanted state to a curved state.

In addition to the way of applying a gate signal (V _gh /V _gl ) for rapid switching between high and low potentials in FIG. 7 , it is also possible to apply a gate signal in a normal state (normal) to achieve the purpose of driving liquid crystal molecules to switch. Please refer to FIG. 8 , in the fifth embodiment of the present invention, during the whole warm-up time, the data signal output terminals (odd and even rows) of the source driver chip 15 are still in high impedance and present a floating state. As for the gate signal output by the gate driver chip 13, the pixel electrode scan signal (Vg) is sequentially supplied to the pixel electrodes in a general scan manner, and is applied to the scan lines (X1, X2, . . . The periodic pulse gate signal on X5) makes the voltage level of the pixel electrode be coupled to a high level close to the gate signal, and can accelerate the liquid crystal molecules in the liquid crystal layer to change from the slanted state to the curved state.

In actual operation, the warm-up time will vary with different products, but generally speaking, the whole warm-up time is about 0-2 seconds; the front part is about 0-0.5 seconds, and the latter part is 0- 1.5 seconds; that is, the ratio of the warm-up time in the front section to the warm-up time in the back section is controlled at about 1:3.

The heating method of the OCB mode liquid crystal display provided by the present invention has quite a lot of advantages. First, according to the design of the present invention, only the existing gate driver chip and source driver chip can be used, and there is no need to increase the high-voltage process of the driver chip. In other words, as long as the setting control of the timing control chip (Tcon) is adjusted, the output signal waveform of the driver chip can be changed, so that the potential of the gate signal is coupled to the pixel electrode, thereby accelerating the transition of the state of the liquid crystal molecules. In this case, the method of the present invention can obviously save the cost of changing the design of the driver chip in the prior art, and couple the high-potential gate signal to the pixel electrode to generate the required heat engine effect.

Claims (16)

1. the hot machine method of a LCD, wherein this LCD has the pixel unit array, and each this pixel unit has comprised a thin film transistor (TFT), this thin film transistor (TFT) can be according to the signal of gate terminal, determine whether conducting, make the data-signal of source electrode be sent to this pixel capacitors, with respect to the opposite side of this pixel capacitors and have and use electrode altogether, and a liquid crystal layer clamping is between this pixel capacitors and this common electrode, and this method comprises the following step at least:

Float this source electrode of this thin film transistor (TFT);

Apply this signal in this grid, thus, the position standard that the voltage level of this pixel capacitors can be coupled and be similar to this signal, and can apply a high voltage in pixel capacitors.

2. the hot machine method of LCD according to claim 1, wherein above-mentioned LCD is an optical compensation bending mode liquid crystal display, and the high voltage that puts on pixel capacitors help to quicken liquid crystal molecule in this liquid crystal layer by oblique exhibition state exchange to case of bending.

3. the hot machine method of LCD according to claim 1, wherein above-mentioned LCD also has the one source pole chip for driving, via a data line, is linked to this source electrode of this thin film transistor (TFT), wherein this source driving chip is to export by interrupting this data-signal, and this source electrode of floating.

4. the hot machine method of LCD according to claim 3, wherein above-mentioned LCD also has a grid drive chip, via a plurality of scanning linears, is linked to all these thin film transistor (TFT)s in this cell array.

5. the hot machine method of LCD according to claim 4, wherein above-mentioned signal is to be periodic pulse signal, and is the cycle along with reference frequency, puts on this thin film transistor (TFT) on same this scanning linear one by one.

6. the hot machine method of LCD according to claim 1, wherein above-mentioned signal has high levels and two kinds of voltage levels of low level, when applying the high levels signal, can this thin film transistor (TFT) of conducting.

7. the hot machine method of LCD according to claim 6 wherein in the portion of hot machine period, is that this signal with high levels is continuously applied in this grid.

8. the hot machine method of LCD according to claim 1 in the portion of hot machine period, is to put on this grid with this signal that high/low position quasi periodic is switched wherein.

9. the hot machine method of an optical compensation bending mode liquid crystal display, wherein this LCD has the pixel unit array, and each this pixel unit has comprised a thin film transistor (TFT), whether this thin film transistor (TFT) can determine conducting according to the high and low current potential of gate terminal signal, and make the data-signal can be via source electrode, drain electrode, be sent to this pixel capacitors, with respect to the opposite side of this pixel capacitors and have and use electrode altogether, and a liquid crystal layer clamping is between this pixel capacitors and this common electrode, and this method comprises the following step at least:

In the hot machine of the leading portion time, float this source electrode of this thin film transistor (TFT), this signal that is continuously applied noble potential simultaneously is in this grid, make the voltage level of this pixel capacitors be coupled in the high levels of this signal, and can quicken liquid crystal molecule in this liquid crystal layer by oblique exhibition state exchange to case of bending;

In the hot machine of the back segment time, to recover the data-signal of this source electrode and supply with, this signal that is continuously applied noble potential simultaneously is in this grid, and via this source electrode and this drain electrode of this thin film transistor (TFT), input data signal is to this pixel capacitors.

10. the hot machine method of optical compensation bending mode liquid crystal display according to claim 9, wherein above-mentioned LCD also has the one source pole chip for driving, via a data line, be linked to this source electrode of this thin film transistor (TFT), wherein this source driving chip is to export by interrupting this data-signal, and this source electrode of floating.

11. the hot machine method of optical compensation bending mode liquid crystal display according to claim 10, wherein above-mentioned source driving chip also has the function of breech lock data signal, can interrupt the transmission of data-signal on all data lines.

12. the hot machine method of an optical compensation bending mode liquid crystal display, wherein this LCD has the pixel unit array, and each this pixel unit has comprised a thin film transistor (TFT), whether this thin film transistor (TFT) can determine conducting according to the high and low current potential of gate terminal signal, and make the data-signal can be via source electrode, drain electrode, be sent to this pixel capacitors, with respect to the opposite side of this pixel capacitors and have and use electrode altogether, and a liquid crystal layer clamping is between this pixel capacitors and this common electrode, and this method comprises the following step at least:

In the hot machine of the leading portion time, float this source electrode of this thin film transistor (TFT), this signal that is continuously applied noble potential simultaneously is in this grid, the voltage level of this pixel capacitors can be coupled be similar to the high levels of this signal, and can quicken liquid crystal molecule in this liquid crystal layer by oblique exhibition state exchange to case of bending;

In the hot machine of the back segment time, recover the data-signal of this source electrode and supply with, put on this grid with the signal recurrent pulse simultaneously, with this thin film transistor (TFT) of conducting, and, import this data-signal to this pixel capacitors by this source electrode and this drain electrode.

13. the hot machine method of optical compensation bending mode liquid crystal display according to claim 12, wherein above-mentioned LCD also has the one source pole chip for driving, via a data line, be linked to this source electrode of this thin film transistor (TFT), wherein this source driving chip is to export by interrupting this data-signal, and this source electrode of floating.

14. the hot machine method of optical compensation bending mode liquid crystal display according to claim 13, wherein above-mentioned source driving chip also has the function of breech lock data signal, can interrupt the transmission of data-signal on all data lines.

15. the hot machine method of optical compensation bending mode liquid crystal display according to claim 12, wherein above-mentioned LCD also has a grid drive chip, via a plurality of scanning linears, is linked to all these thin film transistor (TFT)s in this cell array.

16. the hot machine method of optical compensation bending mode liquid crystal display according to claim 15, wherein the signal of above-mentioned recurrent pulse is the cycle along with reference frequency, puts on this thin film transistor (TFT) on same this scanning linear one by one.

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