JPH02196218A - Driving method for liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain an LCD which has a small image flicker by varying a scanning signal potential in synchronism with the inversion of an image signal and not varying the scanning signal, the image signal, and the potential difference between common potentials, at every field. CONSTITUTION:The driving waveform of the LCD is so set that the image signal 2 is written in picture elements of an (N)th row with a scanning pulse 41 when the polarity is positive or with a scanning pulse 42 when negative and the pulses 41 and 42 differ in peak height. Further, the potential of the part where none of pulses of the scanning signal 3 is applied is made different according to the polarity of the image signal 2. In this constitution, the image signal 2 is inputted from a drain electrode through a TFT for the period of the scanning pulse 41 when the image signal 2 is in a positive to hold charges in liquid crystal. This driving waveform makes scanning pulses that the TFT senses invariably constant irrelevantly to the positive and negative fields to reduce the flickering of the LCD.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a liquid crystal display (LCD) using a thin film transistor (TPT).

(Summary of the Invention) The present invention has been made in order to further reduce flickering of an LCD by changing the scanning signal input to the TPT in synchronization with the image signal.

[Conventional technology]

Conventionally, the input signal of an LCD using TPT has a signal level as shown in FIG.

[Problem to be solved by the invention]

In the driving method described above, the TF depends on the polarity of the image signal.
Because the potential difference between the gate potential and drain potential caused by T is different, the signal written to each pixel of the LCD changes every time the polarity of the image signal is reversed, and this change causes flickering on the screen. Ta.

[Means to solve problems]

In order to solve the above problems, the present invention changes the potential of the scanning signal in synchronization with the inversion of the image signal, so that the potential difference between the scanning signal and the image signal is made equal to the potential difference between the scanning signal and the common potential. be.

[Effect]

According to the above driving method, a flicker-free LCD can be provided.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows driving waveforms of the LCD of the present invention. 1 is a common potential, which is the potential on the side of the substrate (counter substrate) on which no TPT is attached. 2 is an image signal which is input to the drain electrode of the TPT. It is necessary to reverse the polarity of the image signal 2 with respect to the common potential 1 every 1 field (1 field is the period in which the image signal is written once from top to bottom on the entire screen), which means that the DC voltage is applied to the liquid crystal material. This is because adding a bias accelerates the deterioration of the material. 3
is manually applied to the gate electrode of TPT in scan No. 18. 41
．． 42 is the scanning pulse (scanning pulse N) input to the TPT in the Nth row. Image signal 2 is written to the pixels in the Nth row by 41 when the polarity of the image signal 2 is positive with respect to the common potential. , and 42 when the polarity is negative, but the scanning pulses N41 and 42 have different peak heights. Further, the potential of the portion where the pulse of the scanning signal 3 is not included also differs depending on the polarity of the image signal 2. Writing of image signal 2 to pixels using scanning pulses N41 and N42 will be explained with reference to FIG.

FIG. 3 is an equivalent circuit of the pixel section (including TPT). In FIG. 3, 8 is a gate electrode group, and 7 is a drain electrode group. Reference numeral 9 denotes TPT, whose source electrode side is connected to the liquid crystal 10, and the other side of the liquid crystal IO is electrically connected to the common potential 11.

Let us now consider a field in which the image signal 2 is positive.

When the scanning pulse N41 is applied to the gate electrode in the Nth row of the gate electrode group 8, the TPT9 turns on. If we switch back, the switch in the Nth row is turned on,
Image signal 2 enters from the drain electrode through TPT9 only during the period of scanning pulse N41. written signal,
That is, the positive charge stored in the liquid crystal 10 is held until the next scanning pulse N42 arrives. The next image signal 2 is written to T I''T again by the scanning pulse N42.The signal at this time has a negative charge and is opposite in polarity to the previous charge.

The signal writing ability of the TPT9 is determined by the electrical characteristics of the TFTQ itself. An example of this is shown in FIG. In this figure, the drain current I and the source-drain voltage CD S *
This is a characteristic diagram plotted by changing the gate potential V from O to 20 (■) every 5M.This electrical characteristic is the relative potential applied to each terminal of the TPT, that is, the gate electrode group drain 1, and the source bridge. However, as can be seen in Fig. 2, the conventional scanning signal 6 sends a constant scanning pulse in every field, regardless of the polarity of the image signal 5. Therefore, if the polarity of the image signal 5 is positive, If the negative field differs, the relative potential between the terminals of the TPT 9 also differs between fields.Specifically, when the image signal 5 is in the negative field, the scanning pulse becomes relatively large.-All Inventions With the drive waveform, the scanning pulse felt by the TPT 9 is always constant regardless of the positive or negative field.Therefore, the LCD of the present invention has less flicker than the LCD driven with the conventional drive waveform.

〔Effect of the invention〕

As described above, in the present invention, the scanning number 13, the image signal,
The relative potential between each common potential is always constant regardless of the polarity of the image signal, resulting in a good L with little flickering on the screen.
CD) E: Obtained.

[Brief explanation of the drawing]

FIG. 1 is a drive waveform diagram of CD according to the present invention, FIG. 21J is a drive waveform diagram of a conventional LCD, FIG. 3 is an equivalent circuit diagram of a pixel portion, and FIG. 4 is a diagram of electrical characteristics of TPT. l...Common potential 2.5...Image signal 3.6...Scanning signal 9...TPT Applicant Seiko Electronic Industries Co., Ltd. Agent Patent attorney Keiyuki Hayashi Assistant ablA inner ear circuit diagram Figure 3 TFT 17″ltL characteristic diagram Dream 4 figure

Claims (1)

[Claims] In a method for driving a liquid crystal display device in which a plurality of thin film transistors are arranged in a matrix and used as switching elements, the potential of the scanning signal input to the thin film transistor is set such that the potential of the scanning signal input to the thin film transistor is synchronized with the polarity reversal of the image signal input to the thin film transistor. 1. A method for driving a liquid crystal display device, characterized in that a potential difference between the scanning signal, the image signal, and a common potential does not vary from field to field.