JPH0667626A - Liquid crystal driving method - Google Patents

Abstract

PURPOSE:To provide a liquid crystal driving method capable of preventing a drop in contrast and the flickering of a screen. CONSTITUTION:When a liquid crystal panel constituted holding a nematic liquid crystal having relatively high responsiveness is driven by a voltage averaging method, a frame frequency is set at over 80Hz and below 100Hz. As the frame frequency is set high from 80Hz to 100Hz, the period of time for selection is shortened, the response of the liquid crystal during the selection period is made small and thus, the drop in the contrast is prevented and the flickering of the screen is limited for the thining of a frame at the time of a gradation display.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal driving method and, more particularly, to a technique effective for use in a voltage averaging method using a simple matrix type liquid crystal display panel.

[0002]

2. Description of the Related Art When a simple matrix type liquid crystal display panel is driven by a line-sequential type and a voltage averaging method, it is common to make the frame frequency as small as possible without causing flicker. 50-111935
The frequency is set to about 40 Hz to 70 Hz as described in the publication.

[0003]

When a liquid crystal material having a fast response is used, there arises a problem that the liquid crystal material responds with both a selective pulse and a non-selective pulse. In particular, if a response is made with a non-selection pulse, the transmittance at the non-selection level increases in the negative mode, the contrast decreases, and the screen flickers during gradation display.

An object of the present invention is to provide a liquid crystal driving method which prevents the deterioration of contrast and the flickering of the screen. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0005]

The outline of a typical one of the inventions disclosed in the present application will be briefly described as follows. That is, when driving a liquid crystal display panel formed by sandwiching a nematic liquid crystal having a relatively high response by the voltage averaging method, a frame frequency of 80 Hz or more
Set below 00HZ.

[0006]

According to the above means, the frame frequency is 80
Depending on the high setting such as Hz to 100 Hz, the selection period can be shortened and the response of the liquid crystal in the selection period can be reduced, so that it is possible to prevent the deterioration of the contrast, and it is possible to prevent the frame from being displayed in gradation. Flickering of the screen due to thinning can be suppressed.

[0007]

1 is a schematic sectional view of an embodiment of a liquid crystal display panel to which the present invention is applied. In the liquid crystal display panel, pixels are formed at the intersections of scanning line electrodes and signal line electrodes arranged in a matrix. In the figure, 1 is a glass substrate, 2 is a nematic liquid crystal, 3 is a transparent electrode constituting the scanning line electrode and the signal line electrode, 4 is a spacer, 5 is a polarizing plate, and 6 is a drive circuit. A transparent electrode 3 as a scanning line electrode is formed on one of the two glass substrates 1 and a transparent electrode 3 as a signal line electrode is formed on the other of the two glass substrates 1, and a scanning line voltage and a signal line voltage are respectively supplied from a drive circuit 6 to each of them. Supplied. In the figure, only the drive circuit 6 that forms the scanning line voltage is shown.

Although not particularly limited, the signal line drive circuit is arranged separately on both ends of the signal line electrode of the liquid crystal display panel. For example, in the display screen of the liquid crystal display panel, the upper left signal line drive circuit drives the odd-numbered signal electrodes, and the lower right signal line drive circuit in the above display screen drives the even-numbered signal electrodes. Drive the line electrodes. By dividing the signal line driving circuit as described above, the serial input speed can be equivalently doubled, and the pitch of the signal line electrodes arranged at high density can be doubled, thereby configuring the signal line driving circuit. It is possible to secure a mounting space for the semiconductor integrated circuit device.

One semiconductor integrated circuit device forming the signal line driving circuit has a function of driving m signal line electrodes 1 to m. Although not particularly limited, when the number of odd-numbered and even-numbered signal lines in the liquid crystal display panel is larger than m, m signal lines are divided by the semiconductor integrated circuit device forming the plurality of signal line drive circuits. Are driven respectively. The signal line drive circuit is supplied with serial data as pixel data, a clock pulse for capturing the serial data, and a selection / non-selection signal.

The signal line drive circuit takes in pixel data serially input by an input latch circuit which operates in synchronization with the clock pulse. When the pixel data for one line is fetched, it is transferred in parallel to the data latch circuit in synchronization with the data latch signal. When the above-mentioned pixel data is transferred in parallel, the input latch circuit fetches the pixel data corresponding to the next line. The scanning line drive circuit is arranged on the display screen of the liquid crystal panel. The scanning line driving circuit sequentially selects scanning lines extending in the horizontal direction of the liquid crystal panel.

FIG. 2 shows an example of the voltage waveform applied to the liquid crystal. (A) shows a voltage waveform when selected, and (b) shows a voltage waveform when not selected. T1
Is a selection period and T2 is a bias period, T1 + T2
Is the frame period T, and f = 1 / T is the frame frequency. The T1 corresponds to the selection time of one scanning line electrode.

When the drive voltage is Vo, (a) in the selection voltage waveform, the voltage in the selection period is Vo and the voltage in the bias period is Vo / a. On the other hand, in the non-selection voltage waveform (b), the voltage during the selection period is (1-2 / a) V.
and the voltage during the bias period becomes Vo / a. Here, 1 / a is called a bias ratio, and when the number of time divisions is N, (a) the execution value Von of the selected voltage waveform and (b) the execution value Voff of the non-selected voltage waveform are respectively expressed by the following equations (1) and ( It is represented by 2). Von = Vo [[1+ (N-1) / a 2 ] / ^{N]] 1/2 ······ (1) Voff =} Vo [ [a ² -4a + N + 3] / a ² N] ^1/2 · (2) From these equations (1) and (2), Von / Voff becomes maximum when a = N ^1/2 +1.

The liquid crystal 2 shown in FIG. 1 has a viscosity of 19 mPa · S.
Chiral substance S-811 on nematic liquid crystal at (20 ℃)
If a twist angle of 240 ° is used by using a small amount of (made by Merck), N is 200,
Driving at a = 15.1 and f = 90 Hz gives the following results.

FIG. 3 shows (a) the selected waveform and the corresponding transmittance, and (b) the non-selected waveform and the corresponding transmittance under the above conditions. In the figure, (b) the transmittance B2 of the non-selected waveform is small, there is no response during the selection period, and it is possible to prevent flickering of the screen while maintaining sufficient contrast.

FIG. 4 shows a case where the same liquid crystal display panel as described above is used and N = 200, a = 15.1, and only the frame frequency f is driven at 60 Hz as in the conventional case (a).
A selected waveform and its corresponding transmittance, and (b) a non-selected waveform and its corresponding transmittance are shown. When a liquid crystal material having good responsiveness as described above is used and driven at a low frame frequency, the selection period is lengthened by that much, and as a result, the transmittance B2 of the non-selected waveform changes drastically as shown in FIG. The change itself is not perceived by the human eye as a change in transmittance, but the averaged (integrated) transmittance at the time of non-selection increases, and the contrast drops significantly.

As described above, when a liquid crystal material having high responsiveness is used, if it is driven at a conventional frame frequency, the contrast is significantly lowered. For this reason,
When a liquid crystal material with high responsiveness is used, the contrast ratio can be secured by setting the frame frequency high accordingly. Further, even when the frame thinning method is adopted for increasing the number of gradations, the original frame frequency itself is increased, so that it is possible to prevent the flickering of the screen during gradation display.

The response times tr and tf of the TN liquid crystal are expressed by the following equations (3) and (4), respectively. tr = 4πηd ² / (ε ₀ ΔεV ² -4πK ³ ) ... (3) tf = ηd ² / KπK ² ) (4) where η is the viscosity , D is the liquid crystal layer thickness, ε ₀ is the dielectric constant of vacuum, Δε is the discharge anisotropy, V is the applied voltage, and K is the elastic constant.

The γ characteristic of LCD almost depends on the elastic constant K, and when Δφ / γ is specified, the relationship between the response time and the viscosity is as shown in the characteristic diagram of FIG. Under the condition of high time division driving of N = 200 or more, Δφ / γ is considerably limited, so that the response time is considered to be almost determined by ηd ² . When d = 6 μm, η is 20 mP
The present application was effective for liquid crystals of a · S or less. Therefore, the range of high response liquid crystal is ηd ² ≦ 720 mPa · S
・ Specify as μm ² .

In the LCD shown in the embodiment, N = 200, a =
The contrast when driving at a different frequency in 15.1 is shown in the characteristic diagram of FIG. 6, and the flicker is shown in Table 1.

[0020]

[Table 1]

The effects obtained from the above embodiment are as follows. That is, (1) When driving a liquid crystal display panel formed by sandwiching a nematic liquid crystal having a relatively high responsiveness by a voltage averaging method, a frame frequency is 80 Hz.
By setting to 100 HZ or less, the selection period can be shortened and the response of the liquid crystal in the selection period can be reduced, so that the deterioration of contrast can be prevented and the screen flickering due to frame thinning at the time of gradation display can be prevented. The effect of being able to suppress is obtained.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention of the present application is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Needless to say. For example, in FIG.
In the above, any liquid crystal material may be used as long as it has relatively high responsiveness as described above. The frame frequency can be variously set within the above range according to the liquid crystal material, the number of scanning line electrodes, and the like. INDUSTRIAL APPLICABILITY The present invention can be widely used for driving a liquid crystal using a liquid crystal material having high responsiveness by a voltage averaging method.

[0023]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows. That is, when driving a liquid crystal display panel formed by sandwiching a nematic liquid crystal having a relatively high response by the voltage averaging method, a frame frequency of 80 Hz or more
By setting it to 00HZ or less, the selection period can be shortened and the response of the liquid crystal in the selection period can be reduced, so that it is possible to prevent the deterioration of the contrast, and
It is possible to suppress flicker on the screen due to frame thinning during gradation display.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a liquid crystal display panel to which the present invention is applied.

FIG. 2 is a waveform diagram for explaining a liquid crystal driving method according to the present invention.

FIG. 3 is a diagram showing voltage waveforms and transmittances according to the liquid crystal driving method of the present invention.

FIG. 4 is a diagram showing a voltage waveform and a transmittance according to a conventional driving method.

FIG. 5 is a characteristic diagram showing a relationship between response time of liquid crystal and viscosity.

FIG. 6 is a characteristic diagram showing the relationship between the contrast ratio of liquid crystal and frequency.

[Explanation of symbols]

1 ... Glass substrate, 2 ... Nematic liquid crystal, 3 ... Transparent electrode,
4 ... Spacer, 5 ... Polarizing plate, 6 ... Driving circuit.

Claims (1)

[Claims] 1. A liquid crystal display panel in which a nematic liquid crystal having relatively high responsiveness is sandwiched between two substrates provided with transparent electrodes so as to intersect with each other in a matrix on opposite surfaces, and driven by a voltage averaging method. To do this, set the frame frequency to 8
A liquid crystal driving method, characterized in that the range is set to 0 Hz or more and 100 Hz or less.