JP3263415B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matrix type liquid crystal display (LCD), and more particularly to a liquid crystal display driven by an alternating current in synchronization with a horizontal synchronizing signal.

[0002]

2. Description of the Related Art Conventionally, when an image is displayed using a liquid crystal, the liquid crystal is generally driven by an alternating current in order to improve the reliability and life of the liquid crystal. That is, when displaying an interlaced scanning video signal, L having 240 scanning lines is used.
In a case where odd-field and even-field signals are alternately output to a CD to display a one-frame image,
For example, Japanese Patent Publication No. 2-28874 (G09G 3/3)
No. 6) discloses a technique of inverting the polarity of a video signal in synchronization with a field cycle or a horizontal scanning cycle in a television image display by AC driving.

FIG. 5 shows an example of a driving circuit of a liquid crystal panel of a matrix display. Reference numeral a denotes an input video signal, b denotes a synchronization signal separated from the video signal, and 1 denotes a circuit for generating a timing clock sent to the liquid crystal panel driving circuits 2 and 3 from the synchronization separation signal a. The liquid crystal panel drive circuit 2 receives the input video signal a
Is sampled for each line data and output to each data line 4. The liquid crystal panel drive circuit 3 is a gate line drive circuit for sequentially scanning the gate lines 5, and each main circuit is constituted by a shift register. 6 is a liquid crystal pixel, 7 is a switching element connected in series to the liquid crystal pixel 6 and turned on and off according to the output of the gate line driving circuit 3 for outputting a video signal output to the data line 4 by the data line driving circuit 2. It is selectively applied to the electrode of each pixel 6. Reference numeral 8 denotes a common electrode, and when no DC component is applied to the liquid crystal, the potential of the common electrode 8 becomes an optimum predetermined value (a potential at which the absolute levels of the potentials of the video signal and the inverted video signal are roughly equal). However, if the potential deviates from the predetermined value, a DC component is added, and the complete AC drive is not achieved.

That is, when the potential of the common electrode 8 deviates from a predetermined value, the absolute value of the voltage with respect to the common electrode potential applied to the liquid crystal changes and a DC component is added to the liquid crystal, thereby deteriorating the liquid crystal and significantly shortening the life and the like. Cause. Therefore, it is necessary to adjust the potential of the common electrode 8 to a predetermined value.

In the case where the polarity is inverted in synchronization with the field period, as shown in FIG. 9, if the potential of the common electrode 8 deviates from a predetermined value, the brightness of the screen also changes every field. Flicker
r) appears. In such a case, the potential of the common electrode 8 is adjusted to a predetermined value by adjusting the potential of the common electrode 8 so that flicker is not seen while watching the screen on which the image is displayed, and the adjustment can be relatively easily performed as shown in FIG. .

[0006]

In the AC driving of the LCD, besides the method of switching the polarity of the video signal in synchronization with the field period as described above, there is a method of inverting the polarity in synchronization with the horizontal scanning period. In such a driving method, for example, in the odd field, a signal whose polarity is inverted for each line is supplied as shown in FIG. 6, and in the even field, the polarity is inverted for each line in a phase opposite to that of the odd field as shown in FIG. Is supplied.

At this time, if the potential of the common electrode deviates from a predetermined value in the same manner as described above, the voltage applied to the liquid crystal changes every other field in each of the odd and even lines as shown in FIG. The brightness also changes. However,
In a normal video signal, the contents of the video are substantially the same before and after one field, so that flicker also appears on the odd and even lines, and the average brightness of the odd and even fields is also equal. It is hard to catch.

Therefore, even if the flicker is removed by adjusting the potential of the common electrode, the flicker is hard to catch by visual observation, so that the adjustment is very difficult, and there is a possibility that the flicker is adjusted to a position shifted from a predetermined value. The reliability and lifetime of the liquid crystal may be impaired.

[0009]

According to the present invention, there is provided a synchronization separating means for separating a synchronization signal from an input video signal, and a timing control means for generating a timing pulse synchronized with a horizontal scanning period and a field period from the synchronization signal.
16, an adjustment video signal generating means 16 for alternately outputting two types of video signals different in accordance with the timing pulse in synchronization with a field cycle of the input video signal, and the input video signal and the adjustment video signal. Switch means for switching 10
A polarity inversion means 14 for inverting the polarity of the video signal in synchronization with a horizontal scanning cycle by the timing pulse,
An output signal of the polarity inversion means 14 is input, and the polarity of an input video signal is AC-driven with respect to the reference potential with the potential of a common electrode connected to a plurality of liquid crystal pixels arranged in a matrix as a reference potential. The liquid crystal display means 9 for displaying an image, and the common electrode potential adjusting means 15 for adjusting the potential of the common electrode of the liquid crystal display means 9 by changing the potential, and displaying the adjustment video signal on the liquid crystal display means 9 A liquid crystal display device wherein the common electrode potential is adjusted to a predetermined value by operating the common electrode potential adjusting means 15 while watching the image.

[0010]

Since the present invention is configured as described above, even when the polarity of the video signal is inverted in synchronization with the horizontal scanning period, the potential of the common electrode can be visually adjusted to a predetermined value. The absolute levels of the potentials of the inverted video signal and the non-inverted video signal are roughly equal, so that no DC component is applied to the liquid crystal.

[0011]

FIG. 1 shows an embodiment of a liquid crystal display device according to the present invention. FIGS. 2 (i) to (iii) show (A) to (C) of FIG.
It is a waveform diagram of a point.

When the video signal A is displayed on the liquid crystal panel 9, the switch 10 is switched to the position (a). At this time, the input video signal A is supplied to the sync separation circuit 11 and the video / chroma circuit 12.
Is input to The synchronization separation circuit 11 extracts a synchronization signal from the video signal A and outputs it to the timing control circuit 13. The timing control circuit 13 outputs a timing for inverting the polarity of the output signal of the video chroma circuit 12 to the polarity inversion circuit 14, and further outputs a timing pulse for driving the liquid crystal panel 9 by the output signal of the polarity inversion circuit 14. I do. Further, the potential of the common electrode can be adjusted by the common electrode potential adjustment circuit 15.

When adjusting the potential of the common electrode, a switch
10 is switched to the (b) side, and the adjustment video signal C is input from the adjustment video signal generation circuit 16 to the video chroma circuit 12. The adjustment signal generation circuit 16 includes resistors R1, R2, R3 connected in series between the power supply Vcc and the reference potential point, and resistors R2,
A switching transistor TR1 having a collector connected to a connection point of R3, and a resistor connected between the base of the switching transistor TR1 and the timing control circuit 13.
R4. Here, the resistance ratio of the resistors R1, R2 and R3 is set so that R2 / R1 + R2 · Vcc becomes a black level (luminance 0%) as shown in FIG. 2 (iii), and R2 + R3 / R1 + R
2 + R3 · Vcc is set to be a white level (brightness 100%). At this time, the timing pulse B is supplied from the timing control circuit 15 to the adjustment video signal generation circuit 16.
, And the timing pulse B is shown in FIG.
The pulse is synchronized with the video signal A as shown in i).
When the timing pulse B is "H", TR1 turns on and the adjustment video signal C

[0014]

(Equation 1)

## EQU1 ## When the timing pulse B is "L", TR1 is turned off and the adjustment video signal C
Is

[0016]

(Equation 2)

## EQU1 ## Accordingly, the adjustment video signal C has a waveform as shown in FIG. here,

[0018]

(Equation 3)

If the value of the input signal A is made coincident with the pedestal level of the input video signal A, when the timing pulse B is "L", the adjustment video signal C is adjusted to the black level (white 0) of the input signal A. %). further,

[0020]

(Equation 4)

Is set to the white level (black 0) of the input video signal A.
%), The adjustment video signal C is a white level signal when the timing pulse B is “H”.

The driving voltage applied to the liquid crystal panel 9 at this time is as shown in FIG. 3. If the potential level of the common electrode is adjusted to prevent line unevenness on the screen,
As shown in FIG. 4, the potential of the common electrode is adjusted to a predetermined value. After the adjustment is completed, switch 10 is switched to the (a) side to set video signal A
Is displayed on the liquid crystal panel 9.

[0023]

Since the present invention is configured as described above, even when the polarity of the video signal is inverted in synchronization with the horizontal scanning cycle, the user can easily visually observe the potential of the common electrode by applying a DC component to the liquid crystal. Can be adjusted to a predetermined value at which no liquid crystal is applied, thereby improving the reliability of the liquid crystal and extending the life.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a liquid crystal display device according to the present invention.

FIG. 2 is a main part signal waveform diagram of the circuit of FIG. 1;

FIG. 3 is a liquid crystal drive voltage waveform before adjustment when the polarity changes in a horizontal scanning cycle.

FIG. 4 is an adjusted liquid crystal drive voltage waveform when the polarity changes in a horizontal scanning cycle.

FIG. 5 is a structural diagram of a matrix type liquid crystal panel.

FIG. 6 is a liquid crystal drive voltage waveform before adjustment when the polarity changes in a field cycle.

FIG. 7 is a liquid crystal drive voltage waveform after adjustment when the polarity changes in a field cycle.

FIG. 8 is a liquid crystal drive voltage waveform when the polarity changes in a horizontal scanning cycle.

FIG. 9 is a liquid crystal drive voltage waveform before adjustment when the polarity changes in a horizontal scanning cycle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Timing clock generation circuit 2, 3 Liquid crystal panel drive circuit 4 Data line 5 Gate line 6 Liquid crystal pixel 7 Switching element 8 Common electrode 9 Liquid crystal panel 10 Switch 11 Sync separation circuit 12 Video chroma circuit 13 Timing control circuit 14 Polarity inversion circuit 15 Common electrode potential adjustment circuit 16 Adjustment video signal generation circuit

Claims (2)

(57) [Claims] A synchronizing signal separating means for separating a synchronizing signal from an input video signal; a timing control means for generating a timing pulse synchronized with a horizontal scanning period and a field period from the synchronizing signal; Adjustment video signal generating means 16 for alternately outputting two types of video signals having different levels in synchronization with the field period of the input video signal to adjust the common electrode potential.
Switch means 10 for switching between the input video signal and the adjustment video signal, polarity inversion means 14 for inverting the polarity of the video signal in synchronization with a horizontal scanning cycle by the timing pulse, and arranged in a matrix. A plurality of liquid crystal pixels, and inputs the inverted video signal from the polarity inversion means 14 and the potential of the common electrode connected to the plurality of liquid crystal pixels to the plurality of liquid crystal pixels, and sets the potential of the common electrode to Liquid crystal display means 9 for displaying the video signal by AC driving, and a common electrode potential adjusting means 15 for adjusting the potential of the common electrode of the liquid crystal display means 9 by changing the potential. A liquid crystal display device, wherein the common electrode potential is adjusted to a predetermined value by operating the common electrode potential adjusting means 15 while displaying the image on the liquid crystal display means 9 and watching the image. 2. The adjusting video signal output from the adjusting video signal generating means 16 outputs two kinds of signals of a black level signal and a white level signal alternately in synchronization with a field cycle. The liquid crystal display device according to claim 1.