JPH05304647A - Display system for liquid crystal television - Google Patents

Abstract

PURPOSE:To attain a high contrast display with a few flickers by providing a field memory which stores display data for one field at the driving circuit of a liquid crystal television. CONSTITUTION:A field memory 2 is constituted of a memory for one field, and while a digital signal 14 is written in the memory 2 according to a control signal 15 from a control circuit 3, data are read by a control signal 16 whose cycle is 1/2 time as long as the signal 15 from the control circuit 3, which is controlled so as not to pass the writing address, and a signal 19 is transmitted to a signal electrode driving circuit 5. An STN panel 4 is constituted by enclosing a liquid crystal between a substrate having a scanning electrode and the substrate having a signal electrode, and driven by a signal electrode driving circuit 5 and a scanning electrode driving circuit 6 which are controlled by control signals 17 and 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving system of a liquid crystal television using a super twist nematic liquid crystal (hereinafter referred to as STN liquid crystal), and more particularly to a display system for reducing flicker and improving contrast and response speed. ..

[0002]

2. Description of the Related Art A liquid crystal display element in which twisted nematic liquid crystal (hereinafter, referred to as TN liquid crystal) having a twist angle of 90 degrees is enclosed is one of the most widely used liquid crystal elements for liquid crystal televisions. FIG. 4 shows changes in drive signal and transmittance when time-division driving is performed by the voltage averaging method using the liquid crystal display device in which the TN liquid crystal is enclosed. In the figure, (a) is a write signal, (b) is a data signal, and (c) is a transmittance. In this example, only one of the binary display is written at each writing timing.
The transmittance curve changes smoothly. However, as the number of time divisions increases, the ratio between the voltage for lighting the liquid crystal display element and the voltage for non-lighting cannot be taken, and sufficient contrast cannot be obtained.

Here, the voltage transmittance characteristic diagram (T
A liquid crystal having a steeper rise characteristic of the transmittance with respect to a voltage change in the −V curve is required. A liquid crystal that meets this requirement is an STN liquid crystal having a twist angle of more than 90 degrees, and has a rising characteristic that is much steeper than that of a TN liquid crystal. At this time, the change in the transmittance of the STN liquid crystal due to the elliptically polarized light is as high as about 1 msec. By the way, a liquid crystal display device enclosing STN liquid crystal is
When time-division driving is performed by the same method as the liquid crystal display device in which the N liquid crystal is sealed, a new problem which is not in the TN liquid crystal occurs. FIG. 5 shows the drive signal and the transmittance for the liquid crystal display device in which the STN liquid crystal is enclosed.
(B) and (c) correspond to FIG. As shown in FIG. 5C, during one field cycle, the state of high transmittance at the time of selection is changed from the state of high transmittance at the time of non-selection to the desired transmittance while repeating the state of decreasing the transmittance by the display signal for each field. There is. Therefore, this becomes flicker, the contrast is lowered as a whole, and the average transmittance changes as shown by the dotted line, so that the speed at which the target transmittance is reached, that is, the response speed of the transmittance is lowered. The display system of FIGS. 4 and 5 is the NTSC system, and one screen is displayed in two fields.

On the other hand, the inventor of the present application has filed Japanese Patent Application No. 1-2.
In No. 33978, a drive circuit for driving a liquid crystal display element is provided with a field memory for two fields, and while writing data for one field into the field memory, the data of the previous field already written is written. A method of reducing flicker by displaying on a liquid crystal display element a plurality of times is disclosed. With this method, changes in the drive signal and the transmittance when displaying twice in one field are the same as those in FIG. 3, which will be described later in an embodiment of the present invention.

[0005]

According to the driving method of the liquid crystal television provided with the STN liquid crystal display element by the inventor of the present application, the data in the field memory is read a plurality of times during one field and displayed on the liquid crystal display element. Therefore, flicker is reduced and display quality can be significantly improved, but in order to downsize the driving circuit, it is required to reduce the capacity of the field memory. An object of the present invention is to provide a display system of a liquid crystal television capable of displaying a high contrast with less flicker, only by providing a field memory having a smaller capacity.

[0006]

To achieve the above object, the present invention provides a drive circuit of a liquid crystal television with a field memory for storing display data for one field, and the field memory stores one field. In the first half of the period in which the display data is written, the display data of the previous field remaining in the field memory is read and displayed, and in the second half, the newly written display data is read and displayed. To do.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. In FIG. 1, the input video signal 11 is digitized by the A / D converter 1 into a 4-bit digital signal 14 according to the control signal 13 from the control circuit 3 and transferred to the field memory 2. The field memory 2 is composed of a memory for one field, and while the digital signal 14 is being written in the field memory 2 according to the control signal 15 from the control circuit 3, it is controlled so as not to overtake the write address. The control signal 16 is read from the control circuit 3 by a control signal 16 having a cycle slightly more than half the control signal 15, and the signal 19 is transmitted to the signal electrode drive circuit 5. The STN panel 4 has a twist angle of 180 ° to 2 between a substrate having scan electrodes and a substrate having signal electrodes.
70 ° liquid crystal is enclosed, and control signals 17 and 1
It is driven by the signal electrode drive circuit 5 and the scan electrode drive circuit 6 controlled to 8. 3A and 3B show driving signals of the present invention, the read cycle T ₂ from the field memory is the write cycle T ₁ to the field memory (equal to the cycle of one field). 1 /
With a little over two, the signal of the previous field is sent to the panel twice while being written in the memory of one field. In the case of FIG. 3 as well, as in FIG. 4 and FIG. 5, one screen is composed of two fields.

FIG. 2 is a diagram showing the timing of the read address and the write address of the present invention, the horizontal axis is time,
The vertical axis represents the memory address. The solid line indicates the write timing and the dotted line indicates the read timing. The write address is incremented in synchronization with the video signal sent after the vertical blanking interval including the vertical sync signal period, and the addresses are sequentially stored in the memory. The read timing starts within the vertical blanking interval without overlapping the write timing, and ends when the write timing is near the center. The read data at this time corresponds to the data one field before. When the reading is completed, the read address is cleared and the previously written data starts to be read immediately. This reading is controlled so that it ends after the end of writing.
As is apparent from the above description, the reading from the memory is performed twice while the data for one field is written in the memory. Further, the read cycle at this time corresponds to ½ of the sum of the write time and the time of the vertical blanking interval, which is slightly more than ½ of the write cycle.

FIG. 3 shows the drive signal and the transmissivity when driven by the drive system of the present embodiment. (A) is a write signal, (b) is a data signal, and (c) is a transmissivity. is there. As compared with the case where the driving method of the TN liquid crystal of FIG. 5 is used as it is, it can be seen that the flicker in the change of the transmittance in (c) is significantly reduced.

Table 1 shows the response speed and contrast when time-divisionally driven at a duty of 1/200 using the method of the present invention, and the STN liquid crystal display device by the TN liquid crystal driving method without the field memory. This is shown in comparison with the driven conventional example. The response speed indicates the time when the average transmittance shown by the dotted line in FIG. 3C changes from 10% to 90% when a signal that changes from non-lighting to lighting is input, and the contrast ratio is non-lighting. The ratio of lighting darkness is shown. From the table, it can be seen that the contrast ratio is significantly improved and the response speed is also faster.

Table 1

[0012]

As is apparent from the above description, according to the present invention, a liquid crystal television having an STN liquid crystal display element can display a high-speed response and a high contrast only by using a field memory having a small capacity. Is.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing address timing of a field memory according to the present invention.

FIG. 3 is a diagram showing changes in drive signal and transmittance according to an embodiment of the present invention.

FIG. 4 is a diagram showing changes in drive signal and transmittance of a TN liquid crystal display element.

FIG. 5 is a diagram showing changes in drive signal and transmittance of an STN liquid crystal display element.

FIG. 6 is a diagram showing a voltage transmittance characteristic of liquid crystal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 A / D converter 2 Field memory 3 Control circuit 4 STN panel 5 Signal electrode drive circuit 6 Scan electrode drive circuit 11 Video signal 13 Control signal 14 4 bit data signal 15 Control signal 16 Control signal 17 Control signal 18 Control signal 19 4 Bit data signal

Claims (1)

[Claims] 1. A liquid crystal display element in which a liquid crystal (super twist nematic liquid crystal) having a twist angle of more than 90 degrees is sandwiched between a pair of substrates each having a scanning electrode and a signal electrode on opposite surfaces, and a drive for driving the liquid crystal display element. In a liquid crystal television display system in which display data is displayed on the liquid crystal display element of a liquid crystal television having a circuit, the drive circuit is provided with a field memory for storing display data for one field, and the field memory stores one field for one field. In the first half of the period in which the display data is written, the display data of the previous field remaining in the field memory is read and displayed, and in the second half, the newly written display data is read and displayed. LCD television display system.