JPS636854B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multiplex type liquid crystal display driving circuit that is AC driven between a plurality of potential levels.

Generally, a liquid crystal display can obtain a display effect based on the optical anisotropy of the liquid crystal by changing the orientation state of molecules by applied electrolysis. Therefore, in this type of liquid crystal display, it is not necessary to apply a steady current, and if the direct current component is large, electrolysis and other factors may combine to cause the liquid crystal material itself to deteriorate. For this reason, conventional liquid crystal displays have used complicated drive circuits on the premise that they are driven by applying an alternating current voltage of several tens of Hz or more.

FIGS. 1 and 2 show examples of multiplex drive waveforms and drive circuits for TN-type liquid crystal displays, which are conventionally known as the voltage averaging method. The potential levels required to drive the liquid crystal are shown in Figure 1.
5 level. 16 is an example of a signal applied to the scanning electrode side during multiplex driving. 17 is an example of a signal applied to the data electrode side. In FIG. 1, 12 and 14 are symmetrical with respect to potential level 13, and 11 and 15 must also be symmetrical.
The value of each potential level changes depending on the number of electrodes to be multiplexed, and the relative value to the reference level is
It is determined based on the theory of voltage averaging method. Further, its absolute value is determined by the liquid crystal material and changes depending on the operating temperature.

FIG. 2 is a general example of a liquid crystal drive circuit corresponding to FIG. 1. Each circuit element consists of a MOS type FET, and each of the N channel type and P channel type are always connected in pairs. The source potential of each transistor is separated from the substrate potential, and is set to each potential from 11 to 15 in FIG. 1, respectively.
Therefore, in the case of FIG. 2, the number of power supply potential levels required by the entire liquid crystal display drive circuit section is V _DD , V _SS
Including this, there are 7 levels in total.

FIG. 3 shows a liquid crystal drive waveform and its potential level based on the conventional two-frequency method. 35 is an example of a signal applied to the scanning electrode side during multiplex driving, and 36 is an example of a signal applied to the data electrode side. Potential levels 31 and 3
4, and 32 and 33 must be symmetrical to each other about the dashed line. Said symmetry must also be maintained in the temperature correction for the absolute value of each level. The liquid crystal drive voltage in the conventional two-frequency system is about 20V to 40V, and the output circuit for the liquid crystal drive signal 35 or 36 requires a power supply voltage of about 20V to 40V. On the other hand, the so-called logic circuit section at the stage before the liquid crystal drive signal output circuit only needs a power supply voltage of several volts to more than ten volts. 37 and 38 respectively show the potential level of the data signal of the scanning signal on the scanning electrode side. There are six potential levels shown in FIG.

While the conventional liquid crystal display drive circuit required many power supply potential levels and a complicated drive signal output circuit, the present invention provides a drive circuit that uses a small number of power supply potential levels and a simplified output circuit. The present invention provides a circuit that makes it possible to drive a liquid crystal display.

FIG. 4 is a sectional view of a panel of a liquid crystal display and its equivalent circuit. 41 and 42 are the front glass and rear glass of the panel, respectively, and 43 and 44 are transparent electrodes formed on the respective glasses.
45 is formed on the transparent electrode 44, and the liquid crystal 46
This is an insulating layer sandwiched between the electrode 44 and the electrode 44, and is made of a material such as SiO ₂ . Therefore, the liquid crystal and the insulating layer are connected in series between the two electrodes. If the dielectric constant of the insulating layer is sufficiently larger than that of the liquid crystal, or the thickness of the insulating layer is sufficiently smaller than the thickness of the liquid crystal layer, it is necessary to The capacitance of the connected insulating layer has a sufficiently large value, and the voltage generated between the liquid crystal driving electrodes is applied almost as is to the liquid crystal. Therefore, the liquid crystal can be stably driven with an alternating current voltage regardless of the influence of its own direct current resistance and regardless of the applied voltage level, and the direct current component is blocked by the insulating layer. If an insulating layer is formed on top of the electrode 43 and the liquid crystal 46 is sandwiched between the two insulating layers in a sandwich-like manner, the direct current component can be better blocked.

FIG. 5 shows an example of a conventional liquid crystal display 50 in which a capacitor is inserted between each electrode terminal and a drive circuit. The liquid crystal drive circuit output signal is applied to terminal 55 or 56. At this time capacitor 5
3 and 54 must be sufficiently larger than the capacitance of the equivalent capacitor formed between the electrode to which each capacitor is connected and the opposing electrode. In that case, in the same way as the explanation of Fig. 4,
The voltage generated between the liquid crystal drive circuit output terminals 55 and 56 is directly applied to the liquid crystal pixels, and regardless of the potential level of the drive circuit output signal, stable AC voltage drive is performed, and the DC component is transferred to the capacitor 53. , 54.

When a panel structure as shown in FIG. 4 or a circuit configuration as shown in FIG. There is no need to set it so as to maintain symmetry. Therefore, by omitting unnecessary potential levels and setting the potential so that the number of potential levels is the minimum, it is expected that the power supply circuit and the drive circuit will be simplified.

FIG. 6 is a diagram showing an example of potential levels omitted from the conventional example of FIG. 3. The highest potential level is set to GND, and the high level of each of the logic circuit, data electrode application signal output circuit, and scanning electrode application signal output circuit is commonly set to GND. There are 62 low levels of the data electrode application signal output circuit, and 63 low levels of the scan electrode application signal output circuit. At this time, in FIG. 6, the output signal 64 of the data electrode application signal output circuit and the output signal 65 of the scanning electrode application signal output circuit do not have the same amplitude center level, and the potential levels 62 and 63 are changed depending on the temperature characteristics of the liquid crystal, etc. When making corresponding corrections, it is sufficient to use the GND level as a reference. Therefore, there are four potential levels in FIG. 6, two levels less than the six levels in FIG. 3. Also, there are three power supply circuits in Figure 6,
In Figure 3, there are six, so it is halved. Similarly, when driving a TN liquid crystal based on the voltage averaging method, the power supply and circuit can be simplified. It can be reduced to. In addition, the temperature compensation of the potential level in FIG.
Whereas it was necessary to correct a total of four potentials symmetrically between 1 and 34, in Fig. 6, it is only necessary to correct two potentials, 62 and 63, with GND as a reference.

As described above, in the present invention, a liquid crystal is sandwiched between a liquid crystal drive electrode formed on at least one of a pair of substrates sandwiching a liquid crystal, and an output circuit that applies a drive signal to the drive electrode. A capacitor having a larger capacitance than the capacitance interposed between the electrode and the liquid crystal driving electrode formed on the opposing substrate is coupled in series with each electrode to drive the liquid crystal. A liquid crystal drive electrode formed on one of a pair of substrates sandwiching a liquid crystal has at least three types of potential levels. A rectangular signal that inverts between the first potential level and the third potential level is applied to the liquid crystal drive electrode formed on the other substrate, and a rectangular signal that inverts between the first potential level and the third potential level is applied to the liquid crystal drive electrode formed on the other substrate. Since the liquid crystal drive electrodes constitute a matrix type liquid crystal display device consisting of strip-shaped electrodes that are orthogonal to each other, no direct current is applied to the liquid crystal, so that the life of the liquid crystal display device can be extended. Furthermore, since the potential level is small, the power supply circuit can be simplified.

[Brief explanation of the drawing]

FIGS. 1 and 2 are examples of multiplex drive signals and circuits based on the voltage averaging method for conventional TN liquid crystals. FIG. 3 shows an example of a conventional signal based on a two-frequency drive system. 4 and 5 show the structure of a liquid crystal display panel according to the present invention and a simplified example of an equalization circuit. FIG. 6 is an example of a signal of a two-frequency drive system according to the present invention. 16, 35, 65...Scanning electrode drive signal, 1
7, 36, 64...data electrode drive signal, 43,
44... Drive electrode, 45... Insulating layer, 53, 54
...Capacitor.

Claims (1)

[Claims] 1. Between a liquid crystal drive electrode formed on at least one of a pair of substrates sandwiching a liquid crystal and an output circuit that applies a drive signal to the drive electrode, a A capacitor having a capacitance value larger than the capacitance value interposed between the configured liquid crystal driving electrode and the electrode is coupled in series with each electrode, and at least three types of potentials are applied to drive the liquid crystal. A rectangular signal that inverts between a first potential level and a second potential level among the potential levels is applied to a liquid crystal drive electrode formed on one of a pair of substrates sandwiching a liquid crystal. is applied, a rectangular signal that inverts between the first potential level and the third potential level is applied to the liquid crystal drive electrodes formed on the other substrate, and the liquid crystal drive electrodes on the pair of substrates are mutually connected. A matrix-type liquid crystal display device consisting of strip-shaped electrodes that are perpendicular to the .