JPH04180015A - Driving method for liquid crystal electrooptical element - Google Patents

Abstract

PURPOSE:To suppress crosstalks and to eliminate unequal display by respectively outputting the waveforms for displaying on 1st and 2nd scanning electrodes and repetitively outputting both waveforms as a method for outputting the on-pulses of the driving waveforms to be impressed to signal electrodes. CONSTITUTION:The period t1 of the driving waveforms is determined as a 1st frame and the polarities of the impressed voltage are alternated at every selection of the two lines of the scanning electrodes 410. The waveform B is impressed in the period t9, the waveform A in the period t10, the waveform A in the period t11 and the waveform B in the period t12. The periods t7 and t8 are alternately repeated in such a manner. The period t2 is determined as a 2nd frame and this period is so determined that the polarities of the voltage impressed to picture elements 408, 409 on the scanning electrode 410 are reversed when the same scanning electrode 410 as the period t1 and that the waveform B is impressed at the time of the period t2 if the signal electrode waveforms 105, 106 while the same scanning electrode 410 is selected in the periods t1, t2 are selected are the waveform A at the time of the period t1 and that waveform A is impressed at the time of the period t2 when the above-mentioned waveforms are the waveform B at the time of the period t1.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to a method for driving a liquid crystal electro-optical element.

[Prior Art] A driving method for a liquid crystal electro-optical element by multiplexing using a conventional voltage averaging method, in particular a driving method for displaying gradations by pulse width modulation, uses a driving waveform as shown in Fig. 5. The method was as follows.

[Problems to be Solved by the Invention] A conventional drive waveform is shown in FIG. The waveform shown at 502 in FIG. 5 is applied to 405 in FIG. 4, and the waveform at 503 in FIG. 5 is an example of an ideal waveform that should be applied to 406 in FIG. However, the actual waveforms output from the liquid crystal driver 401 in FIG. 4 are as shown by 502 in FIG. 5 and 506 in FIG. This is because the waveform is distorted due to wiring resistance and output resistance of the drive power supply in the liquid crystal driver, or spikes as shown in waveform B of 505 are caused by the influence of other waveforms within the same liquid crystal driver. Voltage fluctuations occur.

Therefore, even though the same effective voltage should be applied to the pixels 408 and 409 in FIG. 4, a difference in effective voltage actually appears, causing crosstalk and deteriorating display quality.

Furthermore, looking at the applied voltage waveform of the liquid crystal electro-optical element before the polarity switching of the applied voltage shown at 603 in FIG. Looking at the waveform of the voltage applied to the liquid crystal electro-optical element when switching the polarity of the applied voltage shown at 606 in b), the effective voltage becomes lower as shown by part D in the selection period t+4.

The main cause of this is due to the influence of voltage changes in the signal electrode waveform, and crosstalk occurs in the lateral direction due to the difference in effective voltage during this selection period.

[Means for Solving the Problems] A method for driving a liquid crystal electro-optical element according to the present invention includes a method for outputting an ON pulse of a driving waveform to be applied to a signal electrode. It is characterized in that waveform B is output as a waveform to be displayed on the second scanning electrode by inputting 8 inputs of waveform A, and waveform A and waveform B are repeatedly output.

[Example] Hereinafter, the details of the present invention will be shown by Examples. In this embodiment, a display mode in which the display data is 4-bit 16-gradation display and black is displayed when no voltage is applied will be described as an example.

(Example 1) FIG. 1 is a drive waveform showing an example of a driving method in Example 1, and FIG. 3 is a diagram showing an example of a gradation pulse waveform in each display data, and the period indicated by t15 is an ON pulse. The width of the ON pulse is the narrowest when the data is oooo, the width of the ON pulse becomes wider as the number increases to 0001, 0010, and the width of the ON pulse is the widest when the number is 1111. In waveform A, the width of the ON pulse is expanded to the left with the right end of the gradation pulse waveform as a reference, and in waveform B, the width of the ON pulse is expanded to the left with the left end of the gradation pulse waveform as a reference.
The width of the pulse is expanded to the right. FIG. 4 is a block diagram showing an example of a liquid crystal display module.
■The drive voltage is determined by resistor division between V9 and V5, and the voltage is received by the voltage follower operational amplifier 412.
vl, V2. V3. Drive voltages V4 and V5 are generated and input to signal electrode drivers 401 and 402 and scan electrode drivers 403 and 404. Then, the scan electrode driver outputs a scan electrode waveform that selects the scan electrodes line-by-line according to the scan line selection signal.
The ideal waveform outputted to is shown at 101 in FIG.

Further, signal electrode waveforms are output from the signal electrode drivers according to display data input to the signal electrode drivers 401 and 402, and an example of an ideal waveform outputted to 405 is shown at 102 in FIG. An example of an ideal waveform output to is shown at 103 in FIG. However, in the actual drive waveform, 101 becomes 104, and 102 becomes 10.
5, and 103 becomes 106.

For example, about half of the output of the signal electrode driver 401 in FIG. It is assumed that ), 40
The display on signal electrode No. 5 is black for the top three pixels, the next five pixels are halftone, and the remaining four pixels are black, and the display on signal electrode No. 406 is black for the top three pixels and the next five pixels. If it is a halftone darker than 405 and the remaining 4 pixels are black, the ideal value is 4°5.
The waveform applied to 405 should be 102 in Figure 1 and the waveform applied to 406 should be 103 in Figure 1, but if you look at the actual waveform, the waveform applied to 405 will be 105. The waveform applied to 406 is as shown in 106. The period t in FIG. 1 is the first frame, and the polarity of the applied voltage is switched every time two lines of scanning electrodes are selected. Looking at the periods t7 and t8 within the period t, waveform B is applied between t9 and waveform A is applied between t+s, so the voltage waveform between t9 and t+ll is There is no change and no effect on the scanning electrode waveform. Furthermore, at the and 1++ points where the polarity of the applied voltage changes, waveform A is applied between tl11 and waveform A is also applied between tl, so the polarity of the voltage applied to the liquid crystal electro-optical element changes. However, there is no change in the voltage actually applied, and there is no effect on the scan electrode waveform. Also, regarding the periods 1++ and tap, waveform A is applied between 1+1 and waveform B is applied between tl2, so there is no change in the voltage waveform between the periods tll and tl2, and the waveform changes to the scanning electrode waveform. There is no influence either. In this way, the period t7 and the period t8 are alternately refined. And t
The period No. 2 is the second frame, and during this period, when the same scan electrode as the period tl is selected, the polarity of the voltage applied to the pixel on the scan electrode is reversed. If the signal electrode waveform when the same scanning electrode is selected in the period t2 is waveform A at tl, it becomes waveform B at t2, and if it is waveform B at tl, it becomes waveform A at t2. That's what I do. By using such a drive waveform, the voltage pulse applied during the selection period of the scanning electrode can be applied without being influenced much by the signal electrode waveform, and moreover, the voltage pulse applied during the selection period of the scanning electrode can be applied without being influenced much by the signal electrode waveform. Since the distortion of the waveform shown in FIG. 10 is averaged over the waveforms 105 and 106, the effective voltage applied to the liquid crystal electro-optical element is less likely to be affected by the display content, and crosstalk can be suppressed.

(Example 2) FIG. 2 shows a driving waveform showing an example of the driving method in Example 2, and is a composite waveform of a scanning electrode waveform and a signal electrode waveform applied to a liquid crystal electro-optic element. The voltage applied to the element is the same as in Example 1. The difference from the first embodiment is that the voltage of the signal electrode waveform is kept low to several volts, and the voltage of the scan electrode waveform is about twice that of the first embodiment. By doing so, the breakdown voltage of the signal electrode driver can be kept extremely low.

In FIG. 2, 201 is the ideal waveform that should be applied to the first line of the scanning electrode, 202 is the ideal waveform that should be applied to the second line, and 203 is the ideal waveform that should be applied to the third line. 204 and 205 are the ideal waveforms that should be applied to the signal electrode. This is an example of a waveform. However, in actual driving waveforms, 201 becomes like 206, 204 becomes like 207, and 205 becomes like 208. The driving waveforms of 206, 207, and 208 correspond to the driving waveforms of Example 1, and the waveforms of 206, 105, 207, 208 instead of 104 correspond to those of the liquid crystal display as shown in FIG. When applied to the spray module, the composite voltage applied to each pixel is the same as in Example 1, so the voltage pulse applied during the selection period of the scanning electrode is the signal electrode waveform, similar to that described in Example 1. The liquid crystal electro-optical The effective voltage applied to the element is less likely to be affected by the displayed content, and crosstalk can be suppressed.

In this embodiment, the polarity is switched every two lines of scanning electrode selection, but this can be done every any number of lines. For example, the shape of the signal electrode waveform in the case of switching every four lines is different from that of the positive polarity. If the order is waveform A, waveform B, waveform A, waveform B in negative polarity, waveform B, waveform A, waveform B in negative polarity.
, liquid form A, and if the order is waveform B, waveform A, waveform B, and fTL form A for positive polarity, the order is waveform A, waveform B, waveform A, and waveform B for negative polarity. The number of lines for this polarity switching may be any number of lines, but it is particularly preferable to switch the polarity for every 2n (n is an integer) line.

In addition, in this embodiment, 16 gradations have been explained, but no matter how many gradations there are, driving can be done using the same concept, and even in the case of binary display, driving is performed using the waveforms shown by the data 0000 and 1111 in Figure 3. do it.

U Effects of the Invention As described above, according to the present invention, distortion of the applied voltage waveform when selecting the scanning electrode and distortion of the signal electrode liquid shape due to the wiring resistance and output resistance of the power supply line in the signal electrode driver can be avoided. Display unevenness can be eliminated and a display with higher display quality can be provided.

[Brief explanation of drawings]

FIG. 1 is a timing chart showing drive waveforms in Example 1 of the present invention. FIG. 2 is a timing chart showing drive waveforms in Example 2 of the present invention. FIG. 3 is a diagram showing gradation pulse waveforms of waveform A and waveform B. FIG. 4 is a block diagram showing an example of a liquid crystal display module. FIG. 5 is a timing chart showing conventional drive waveforms. FIG. 6 is a timing chart showing waveforms when scanning electrodes are selected using conventional drive waveforms. 101: Ideal scanning electrode waveform 102.103: Ideal signal electrode waveform 104: Actual scanning electrode waveform 105.106: Actual signal electrode waveform 201.202
, 203: Ideal scanning electrode waveform 204.205:
Ideal signal electrode waveform 206 + Actual scanning electrode waveform 207.208 + Actual signal electrode waveform 401.402
: Signal electrode driver 403, 404: Scanning electrode driver 405, 406: Signal electrode waveform 407: Scanning electrode waveform 408, 409: Pixel 410: Scanning electrode 411: Signal electrode 412: Operational amplifier or above Representative of Seiko Epson Corporation Patent attorney Kizobe Suzuki (1 person) Figure 4

Claims (3)

[Claims] (1) At least in a method of multiplex driving a liquid crystal electro-optical element in which a liquid crystal is sandwiched between a substrate on which a scanning electrode is formed and a substrate on which a signal electrode is formed, an ON pulse of a driving waveform is applied to the signal electrode. As an output method, waveform A is output as a waveform to be displayed on the first scanning electrode, waveform B is output as a waveform to be displayed on the second scanning electrode, and waveform A and waveform B are A method for driving a liquid crystal electro-optical element characterized by repeated output. (2) Waveform A and waveform B are alternately repeated while the polarity of the voltage applied to the liquid crystal electro-optical element is the same, and the same waveform continues where the polarity of the applied voltage changes. A method for driving a liquid crystal electro-optical element according to item 1. (3) The liquid crystal electro-optical element according to claim 1 or 2, wherein the polarity of the voltage applied to the liquid crystal electro-optical element is switched every n scanning lines (n is an integer). Driving method.