JPH0534659A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To offer the liquid crystal display device which suppresses panel driving power consumption at the time of driving a memory, and also, reduces a flicker. CONSTITUTION:The device is provided with a liquid crystal panel for inverting spontaneous polarization by applying an electric field from the outside by using a liquid crystal for showing ferroelectricity in which the spontaneous polarization concerned exists in a state that an electric field is not applied from the outside, a pulse voltage applying means 2 for applying a pulse voltage of a prescribed voltage value to a ferroelectric liquid crystal, and a data comparing means for comparing image data to be displayed on the liquid crystal panel 1 and image data displayed at present, and constituted so that a scanning non- selection voltage is set to the same voltage as a data non-selection voltage as a driving voltage of the liquid crystal panel 1 by the pulse voltage applying means 2 in a period in which data is not changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device,
Specifically, it relates to a liquid crystal display device using a ferroelectric liquid crystal, which is suitable for use in the field of flat panel displays.
In recent years, fast response speed, wide viewing angle,
Ferroelectric liquid crystal (FL)
A liquid crystal display device using C: Ferroelectric Liquid Crystal has been receiving attention.

Ferroelectric liquid crystal refers to one in which the smectic C phase exhibits ferroelectricity in the arrangement of liquid crystal molecules, that is, one in which the spontaneous polarization of the smectic C phase liquid crystal molecule is extremely large. General liquid crystal, eg TN
(Twisted Nematic), STN (Super Twisted Nemati)
Unlike c), which is displayed by using the dielectric torque generated by an electric field, it has a memory effect (memory characteristic) by its own bistable state.

However, since the panel gap of the ferroelectric liquid crystal is about ⅓ of the STN liquid crystal display device, the cell capacity becomes about three times, and such a liquid crystal display device usually has the structure shown in FIG. Since the driving is performed by the 1/4 bias method as shown in (1), the cell voltage is generally high, and if the scanning drive is always performed for image display, a driving power larger than that of the STN liquid crystal display device is required and power consumption is increased. It is disadvantageous in terms of electricity.

Therefore, in order to take advantage of the excellent characteristics of the ferroelectric liquid crystal, it is necessary to suppress the power consumption during driving.

[0005]

2. Description of the Related Art Conventionally, as shown in FIG. 6, a liquid crystal display device using a ferroelectric liquid crystal has been driven by a black color including initialization (indicated by a black circle in the drawing) for a liquid crystal cell forming a pixel. (2) and writing of white (indicated by ◯ in the figure) including initialization are combined into one set to perform writing on one screen, that is, so-called AC driving is general.

In this case, as the drive driver, a 4-value output STN driver is used, and the bias ratio of the drive voltage is between the selected cell voltage and the half-selected cell voltage because the ferroelectric liquid crystal has a peak value response. To maximize the ratio,
The 1/4 bias method described above is used. For this reason,
The data non-selection voltage is the same voltage regardless of the state of the alternating signal (DF).

As a method of writing black (hereinafter referred to as a dark cell) including initialization and writing white (hereinafter referred to as a bright cell) including initialization by the above-described 1/4 bias method, for example, When the pattern shown in FIG. 7 is used as a display pattern, as shown in FIG. 8, a dark cell (●) and a bright cell (◯) are written in each of the first field and the second field which form one frame, Two-field driving method and dark cell (●) for each scanning line as shown in FIG.
There is known a 4-pulse driving method or the like for writing a light cell and a bright cell (◯).

[0008]

However, in such a conventional liquid crystal display device, the output waveform from the scan driver is 1 V and 3 V during the non-selection period due to the functional limitation of the driver. The voltage is output according to the alternating signal (DF), and the cell applied voltage goes back and forth between ± 1V.

That is, the ferroelectric liquid crystal is driven when the memory is driven by utilizing the fact that the ferroelectric liquid crystal has a memory effect when it is in the 0V state, and when the memory is driven, power consumption is originally required. In spite of the memory drive state, there is a problem that the charging / discharging current flows through the display panel, power is consumed by the electrode resistance, and the display image flickers, so-called flicker occurs. ..

[Object] Therefore, an object of the present invention is to provide a liquid crystal display device which suppresses panel driving power consumption at the time of driving a memory and reduces flicker.

[0011]

In order to achieve the above object, the liquid crystal display device according to the present invention uses a ferroelectric liquid crystal in which spontaneous polarization exists in the absence of an external electric field, and an external electric field is applied to the liquid crystal display device. A liquid crystal panel for reversing the spontaneous polarization, a pulse voltage applying means for applying a pulse voltage of a predetermined voltage value to the ferroelectric liquid crystal, image data to be displayed on the liquid crystal panel, and an image currently displayed. Data comparison means for comparing data with each other. As a result of the data comparison by the data comparison means, a scan non-selection voltage is not selected as data as a drive voltage of the liquid crystal panel by the pulse voltage application means during a period when data is not changed. The voltage is set to be the same as the voltage.

[0012]

According to the present invention, as a result of comparison of data by the data comparison means, the scanning non-selection voltage becomes the same voltage as the data non-selection voltage as the drive voltage of the liquid crystal panel by the pulse voltage application means during the period when the data is not changed. The charging / discharging current flowing through the liquid crystal display panel is prevented.

That is, since the charging / discharging current is prevented, the panel driving power consumption at the time of driving the memory is suppressed and the flicker is prevented.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 and 2 are diagrams showing an embodiment of a liquid crystal display device according to the present invention, FIG. 1 is a block diagram showing the whole constitution thereof, and FIG. 2 is a circuit diagram showing the constitution of the main part thereof. First, the configuration will be described.

The liquid crystal display device of this embodiment is roughly classified into a liquid crystal panel 1, a pulse voltage applying means 2 and a data comparing means 3.
Further, the pulse voltage applying unit 2 includes the data driver 4, the scan driver 5, and the power supply circuit 6, and the data comparing unit 3 includes the control signal generating unit 7, the frame memory 8, the comparing circuit 9, and the gate circuit 10. It consists of

HS is a horizontal synchronizing signal, VS is a vertical synchronizing signal, CLK is a clock, XCP is a display data transfer clock, LP is a display data latch pulse, DF is an AC signal, FRM is a scan line signal, and YCP is a scan. A line shift clock, NS is a screen update signal, XD is panel display data, and CMP is a comparison result signal. LCD panel 1
Is an LCD panel using a ferroelectric liquid crystal having m × n pixel display pixels.

The pulse voltage application means 2 selectively applies the bias voltages of 0, 1, 2, 3, 4 V generated in the power supply circuit 6 to the liquid crystal panel 1. Here, the power supply circuit 6 has an output voltage changing circuit 11 as shown in FIG. 2, and the output voltage changing circuit 11 is composed of a resistor R, analog switches SW1 and SW2, and buffer amplifiers B1 to B5. There is.

The data comparison means 3 compares the image data to be displayed on the liquid crystal panel 1 input from the outside with the image data currently displayed on the frame memory 8 by the comparison circuit 9, and outputs both data. The comparison result signal CMP, which is information indicating whether or not is the same, is output to the control signal generator 7. Next, the operation will be described.

3 and 4 show examples in which the present embodiment is applied to the two-field driving method and the four-pulse driving method. Since the display data input from the outside is matched with the writing speed of the liquid crystal display device, it is first taken into the frame memory 8 and, at the same time, is compared with the data of the previous screen by the comparison circuit 9.

In the comparison result by the comparison circuit 9, information indicating that the comparison or non-coincidence is output in dot units or line units to the control signal generation unit 7 as the comparison result signal CMP, and the non-coincidence information is output as the comparison result signal CMP. Is output, the control signal generator 7 suspends the loading of the display data into the frame memory 8 at the end of the frame currently being loaded.

Next, the control signal generator 7 outputs NS of "H".
Is output to the power supply circuit 6, and the analog switches SW1 and SW2 in the output voltage changing circuit 11 are switched by NS. That is, the scanning non-selection voltage is switched by the analog switches SW1 and SW2 depending on the state of NS, and when there is a change in the display content, NS is controlled by the control signal generator 7 so as to be "H". The analog switches SW1 and SW2 are controlled to be connected to the b side when NS is "L", and similarly to the a side when NS is "H". As a result, the scanning non-selection voltage is switched to the same potential as the data non-selection voltage when there is no change in the display content.

In this way, the power supply circuit 6 raises the power supply voltage to each voltage, and the data driver 4,
And a new display data for one screen for updating the screen is transferred together with the output to the scan driver 5, and when this transfer is completed, the control signal generating unit 7 again causes the frame memory 8 of the display data from the outside. Importing into and the comparison with the display data are restarted. NS of FRM is "L"
Is controlled so that it is not output when.

As described above, in this embodiment, the output voltage of the scan driver is set to DF during the memory operation in which NS is "L".
The same as the output voltage of the data driver, that is, the cell applied voltage can be set to 0V regardless of the state of, so that the panel power consumption during the memory operation can be reduced, and especially when the frequency of the screen update is low, the power consumption can be reduced. Can be significantly reduced.

Further, by suppressing the potential fluctuation, the occurrence of flicker can be suppressed and a very easy-to-see display screen can be obtained.
Therefore, when there is no change in the display content, the driving power can be reduced, and a liquid crystal display device using low power consumption and flicker-free ferroelectric liquid crystal can be realized. Although the example using the frame memory has been described in the above embodiment, if the data transfer rate from the outside is suitable for the writing speed of the liquid crystal display device, the 1H delay line memory is sufficient.

[0025]

According to the present invention, as a result of the data comparison by the data comparison means, the scanning non-selection voltage is set to the same voltage as the data non-selection voltage as the drive voltage of the liquid crystal panel by the pulse voltage application means during the period when the data is not changed. It can be set, and the charging / discharging current flowing in the liquid crystal display panel can be prevented.

Therefore, it is possible to suppress the panel driving power consumption during the memory driving and prevent the occurrence of flicker.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a liquid crystal display device of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a main part of this embodiment.

FIG. 3 is a timing chart of the two-field driving method according to the present embodiment.

FIG. 4 is a timing chart of the 4-pulse drive method according to the present embodiment.

FIG. 5 is a diagram for explaining the 1/4 bias method.

FIG. 6 is a diagram for explaining driving and display principles of a ferroelectric liquid crystal display device.

FIG. 7 is a diagram showing an example of a display pattern.

FIG. 8 is a timing chart of a conventional two-field driving method.

FIG. 9 is a timing chart of a conventional 4-pulse drive method.

[Explanation of symbols]

 1 liquid crystal panel 2 pulse voltage applying means 3 data comparing means 4 data driver 5 scanning driver 6 power supply circuit 7 control signal generating section 8 frame memory 9 comparing circuit 10 gate circuit 11 output voltage changing circuit R resistance SW1, SW2 analog switches B1 to B5 Buffer amplifier

Front page continuation (72) Inventor Hiroshi Murakami 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (1)

[Claims] 1. A liquid crystal panel in which a spontaneous polarization is present in the absence of an external electric field and which exhibits ferroelectricity, and which inverts the spontaneous polarization by externally applying an electric field, and the ferroelectric liquid crystal panel. The liquid crystal panel includes pulse voltage applying means for applying a pulse voltage having a predetermined voltage value, and data comparing means for comparing the image data to be displayed on the liquid crystal panel with the currently displayed image data. As a result of the data comparison, the liquid crystal display device is characterized in that the scan non-selection voltage is set to the same voltage as the data non-selection voltage as the drive voltage of the liquid crystal panel by the pulse voltage applying means during the period in which the data is not changed.