JPH0731485B2 - Liquid crystal display - Google Patents

Description

The present invention relates to a liquid crystal display device, and more particularly to an active matrix type liquid crystal display device in which an active element is provided for each pixel electrode.

(B) Prior Art FIG. 6 is a partial structural explanatory view of a conventional active matrix type liquid crystal display device, and shows a plurality of video signal lines S1, S2, S3, ..., Sn provided in parallel in the vertical direction. , And a plurality of scanning lines G1, G2, G3, ..., Gm provided in parallel in the horizontal direction, and a pixel electrode a arranged corresponding to each intersection, and a counter electrode facing the pixel electrode a. A video signal is supplied to a liquid crystal cell c having a counter electrode b connected to a line E via an active element d, and interlaced scanning is performed by signals from scan lines G1, G2, G3, ..., Gm to form an image. Is displayed.

Generally, in a liquid crystal display device that requires AC drive, the polarity of a signal is inverted in every scan period of all liquid crystal cells c (period of scanning all arranged pixel electrodes a). Driving is performed, and the driving frequency of the liquid crystal is half the scanning frequency of all the liquid crystal cells c.

If this drive frequency falls below approximately 30 Hz, flicker (flicker on the screen) occurs.

In an active matrix type liquid crystal display device, when an image is displayed by interlaced scanning of a television signal of the NTSC system, the number of scanning lines (the number of scanning lines m) of the liquid crystal panel (panel in which the liquid crystal cells c are arranged) is In the case of partial screen display with the number of effective display scanning lines (240 lines) or less for one field of the signal, the liquid crystal panel is driven by overlapping the odd field signal and the even field signal of the television signal. 1/2 the frequency, or 30Hz
Next, flicker is not a problem. However, when the number of scanning lines of the liquid crystal panel indicates a full screen display of the number of effective display scanning lines (480 lines) for one frame of the television signal, the liquid crystal driving frequency is 1/2 of the frame frequency, that is, 15H.
It becomes z and flicker becomes a problem.

Several driving methods have been proposed to solve this problem. One of them is a method in which two scanning lines G1, G2, G3, ..., Gm are combined, and the combination of the two is changed for each field, and two scanning lines are simultaneously driven by the in-phase video signal. The other one uses a frame memory or the like to scan one horizontal scanning line Gi (i =
The image data for two video signal lines is displayed within the scanning period of 1 to m). However, the former leads to a decrease in vertical resolution because two scanning lines G1, G2, G3, ..., Gm are driven simultaneously with the same signal, and the latter requires a large-capacity memory corresponding to the number of display liquid crystal cells c. , Active element d
It is necessary to increase the clock frequency of the driving driver for driving the drive circuit, which increases the cost (see Japanese Patent Laid-Open No. 61-239787).

Therefore, a method compatible with the current television system has been proposed, which does not reduce the vertical resolution and requires almost no additional hardware. This is a driving method in which the polarities of the video signals of the liquid crystal cells c adjacent to each other in one horizontal scanning line Gi (i = 1 to m) are mutually reversed (Journal of the Television Society, Vol.40, No. 40). .10 (1986) Paper Special,
Flat display technology, posted).

By the way, some liquid crystals have normal white and normal black optical characteristics. The former has the highest light transmittance in the steady state, and the voltage value is increased even when the applied voltage V is increased.
The light transmittance does not change up to Va (threshold value), but when it exceeds it, the light transmittance begins to decrease, and the light transmittance becomes the lowest at the voltage value Vb. On the contrary, the latter has the lowest light transmittance in the steady state, and the light transmittance does not change up to the voltage value Va even when the applied voltage V is increased, but beyond that, the light transmittance begins to increase and the voltage The light transmittance becomes highest at the value Vb. Therefore, in the liquid crystal display, the image is displayed by changing the applied voltage V of the video signal from Va to Vb in the range where the light transmittance changes. At this time, if the applied voltage V is sufficiently close to the voltage value Vb. The normal white liquid crystal can sufficiently block the transmitted light, and the normal black liquid crystal can sufficiently transmit the transmitted light, thereby enhancing the contrast of the image. In order to bring the applied voltage V sufficiently close to the voltage value Vb, it is sufficient to supply a stable voltage with a small amplitude and good response characteristics from the video signal side. A bias driving method is used in which a bias voltage corresponding to the above-described voltage value Va is applied to the electrode b side in advance and the applied voltage V on the video signal side is varied only between Va and Vb.

(C) Problems to be solved by the invention However, in order to eliminate flicker, the polarities of the video signals of the liquid crystal cells c adjacent to each other in one horizontal scanning line Gi (i = 1 to m) described above are eliminated. When a driving method of inverting each other is used, in a conventional active matrix type liquid crystal display device, a counter electrode b facing a pixel electrode a
However, since all are connected to the counter electrode line E, it is impossible to apply a bias voltage corresponding to the voltage value Va in advance to the counter electrode b side. Therefore, the applied voltage V is changed to the voltage value Vb. It is difficult to get close enough to
There is a problem that it is difficult to display an image with high contrast.

The present invention has been made in order to solve such a problem, and applies a bias voltage to the counter electrode b corresponding to the polarities of the video signals which are inverted with respect to each adjacent liquid crystal cell c. The present invention provides an active matrix type liquid crystal display device capable of displaying a high-contrast image without flicker.

(D) Means for Solving the Problems In the present invention, a plurality of video signal lines arranged in parallel in the vertical direction and a plurality of scanning lines arranged in parallel in the horizontal direction are arranged corresponding to respective intersections. In the active matrix type liquid crystal display device in which a video signal is supplied to the picture element electrode via an active element and interlaced scanning is performed by a signal from the scanning line, a scanning signal supply means for supplying a signal to the scanning line, A first video signal supplying means for supplying the first video signal to the odd-numbered columns of the video signal line, and a second video signal for which the polarity of the first video signal is inverted to the even-numbered columns of the video signal line Two video signal supply means, first and second picture element electrodes to which the first picture signal and the second picture signal are respectively supplied, a first counter electrode facing the first picture element electrode, and a second picture element electrode Opposed to Second counter electrode, first counter electrode signal supplying means for supplying the first counter electrode signal to the first counter electrode, and second counter electrode for the second counter electrode in which the polarities of the first counter electrode signal are reversed. It is characterized in that it comprises a second counter electrode signal supply means for supplying a signal.

(E) Action Since the first video signal and the second video signal have a half-cycle phase difference with each other, and the first counter electrode and the second counter electrode also have a half-cycle phase difference with each other, the video A bias voltage can be applied to the counter electrode corresponding to the polarities of the video signals that are inverted with respect to each of the liquid crystal cells of the odd and even lines of the signal, and a high-contrast image without flicker is displayed. It

(F) Embodiment Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings.

FIG. 1 is a partial configuration explanatory view showing a partial configuration of an embodiment of an active matrix type liquid crystal display device of the present invention.

1, 2, 3, and 4 are video signal lines, 1 and 3 are first video signal lines in odd columns, 2 and 4 are second video signal lines in even columns, and 5 is a first video signal supply. Circuit, 6 is second
This is a video signal supply circuit.

7 to 10 are scanning lines. Reference numeral 11 is a scanning signal supply circuit. 12
Reference numerals 19 to 19 denote first pixel electrodes to which the first video signal is supplied. 20-27
Is a thin film transistor connected to the first video signal lines 1 and 3. 28 to 35 are second picture element electrodes to which the second video signal is supplied.
36 to 43 are thin film transistors connected to the second video signal lines 2 and 4.

Further, 44 to 51 are first counter electrodes facing the first picture element electrodes 12 to 19, 52 to 59 are second counter electrodes facing the second picture element electrodes 28 to 35, and 60 is a first counter electrode. A signal supply circuit, 61 is a second counter electrode signal supply circuit, and 62, 63, 64 and 65 are first picture element electrode 12, second picture element electrode 28, first picture element electrode 13 and second picture element. The first and the first corresponding to the electrodes 29, respectively
The second, third and fourth liquid crystal cells.

The video signals are supplied to the first picture element electrodes 12 to 19 through the thin film transistors 20 to 27, respectively, from the first picture signal supply circuit 5, and to the second picture element electrodes 28 to 35. The second video signal is supplied from the second video signal supply circuit 6 via the thin film transistors 36 to 43, respectively. Then, interlaced scanning is performed to display an image. The scanning order is such that in the odd field, the scanning signal is supplied from the scanning signal supply circuit 11 to the scanning lines 7 and 9 in the odd-numbered rows, and the thin-film transistors 20, 36, 24. , 40 are turned on to supply the first video signal to the first pixel electrodes 12 and 16 and the second video signal to the second pixel electrodes 28 and 32, and then the thin film transistors 22, 38, 26. , 42 are turned on to supply the first video signal to the first picture element electrodes 14 and 18, and the second video signal to the second picture element electrodes 30 and 34. Then, in the next even field, the scanning signal is output from the scanning signal supply circuit 11 to the even-numbered scanning lines 8 and 10, and the thin film transistors 21, 37,
The gates of 25 and 41 are turned on so that the first picture signal is supplied to the first picture element electrodes 13 and 17, and the second picture signal is supplied to the second picture element electrodes 29 and 33. The gates of 27 and 43 are turned on so that the first picture signal is supplied to the first picture element electrodes 15 and 19 and the second picture signal is supplied to the second picture element electrodes 31 and 35.

FIG. 2 is a timing chart showing the operation of the first liquid crystal cell 62, the second liquid crystal cell 63, the third liquid crystal cell 64, and the fourth liquid crystal cell 65 in the interlaced scanning of the four liquid crystal cells.

(A) is a sync signal of odd and even fields for image display, the frequency is 60 Hz, and one screen, that is, one frame is composed of 30 Hz between the dotted lines 101 and 102. (B) and (c) are scan synchronization signals of the scan lines 7 and 9 in the odd field, respectively. (D) and (e) are scan synchronization signals of the scan lines 8 and 10 in the even field, respectively. (F) is an analog sample hold signal corresponding to the video signal voltage supplied to the first picture element electrode 12, is output from the first video signal supply circuit 5, and the voltage value changes between V1 and V2. .

(G) to (g) are models of the same signal as (g), and are the four first picture element electrodes 12, the second picture element electrodes 28, and the first picture element electrodes 28.
The first pixel electrode 13 and the second pixel electrode 29 are supplied to the first
And (2) are the drive polarities of the second liquid crystal cell, (G) is the drive polarity of the first liquid crystal cell 62, (H) is the drive polarity of the second liquid crystal cell 63, and (R) is the drive polarity of the third liquid crystal cell 64. , (Nu) indicate the drive polarity of the fourth liquid crystal cell 65, and (ru) to (f) indicate the first, second, third, and fourth corresponding to the signals (g) to (nu). Liquid crystal cell 62,63,64,6
5 is the optical response of each.

As shown in FIG. 2, first in the odd field, the signal (g) from the first video signal supply circuit 5, the signal (h) from the second video signal supply circuit 6, and the scan synchronization signal of the scan line 7. It is output in synchronization with (b). In the next even field, the signal (i) is output from the first video signal supply circuit 5 and the signal (d) is output from the second video signal supply circuit 6.
90 ° from the odd field signal in synchronization with
It is output with a delay of 4 cycles. At this time, the drive polarity signal (h) of the second liquid crystal cell 63 is 180 ° with respect to the drive polarity signal (g) of the adjacent first liquid crystal cell 62, that is, a half cycle (1/2).
It has a phase difference of (cycle) and the phase is inverted. Similarly, the drive polarity signal (nu) of the fourth liquid crystal cell 65
It has a half-cycle phase difference with respect to the drive polarity signal (i) of the adjacent third liquid crystal cell 64. (Y) is a combined optical response obtained by combining optical response No. (L) to optical response (F), and the four first, second, third, and fourth liquid crystal cells 62, 63, 64, 65 are
When viewed as two blocks, the optical response is 60 Hz, which shows that flicker can be eliminated by this driving method.

FIG. 3 is a graph showing an example of the relationship between the applied voltage (effective value) and the light transmittance of the liquid crystal cell of the normal white characteristic used in this example.

In the figure, R, G, and B indicate different measurement wavelengths, and R is red light (6
32 nm), G represents green light (520 nm), and B represents blue light (488 nm). The light transmittance of the liquid crystal cell is high when the applied voltage V = 0 and is a bright color display, and as the applied voltage V is increased, the light transmittance is bordered by the voltage value Va (threshold value). Begins to decrease, the light transmittance is the lowest at the voltage value Vb,
The display is dark.

FIG. 4 is a timing chart showing applied voltage signals of the first liquid crystal cell 62 and the second liquid crystal cell 63 which are adjacent to each other when a dark color display is performed using a liquid crystal cell having a normal white characteristic, and threshold values are shown for each. In order to apply a voltage corresponding to the above, the first counter electrode signal and the second counter electrode signal are supplied to the first counter electrode 44 and the second counter electrode 52, respectively.

(A) is a sync signal for odd and even fields for image display, similar to FIG. 2 (A). 2 (f) is the same signal as in FIG. 2 (f), which is an analog sample hold signal corresponding to the video signal voltage supplied to the first pixel electrode 12, and is output from the first video signal supply circuit 5 The value changes between V1 and V2. (SO) is an analog sample hold signal supplied to the second picture element electrode 28,
It is output from the video signal supply circuit 6 and has a phase difference of a half cycle with the signal (re). (T) and (N) are the bias voltages of the first counter electrode signal supplied to the first counter electrode 44 and the second counter electrode signal supplied to the second counter electrode 52 in advance, and the voltage values It changes in two ways: low level of V3 and high level of voltage value V4. The signal (ne) has a half-cycle phase difference with respect to the signal (tsu). (A) and (ra) are signals of the applied voltage applied to the second liquid crystal cell 63 of the first liquid crystal cell 62, respectively.

The adjacent first liquid crystal cell 62 and second liquid crystal cell 63 are scanned from the first video signal line 1 and the second video signal line 2 when the scanning line 7 is scanned and the gates of the thin film transistors 20 and 36 are made conductive. , A signal (re) and a signal (so) are supplied, respectively. At this time, the first counter electrode 44 and the second counter electrode 52
Since a bias voltage signal (tsu) and a signal (ne) are respectively supplied to the first liquid crystal cell 62, the voltage applied to the first liquid crystal cell 62 (na) = signal (re) −signal (tsu), Signal (La) applied to liquid crystal cell 63 = Signal (So) -Signal (Ne)
Then, the signal (na) is applied to the first liquid crystal cell 62 and the signal (la) is applied to the second liquid crystal cell 63, respectively, and the maximum value (V1
The amplitude changes from -V3) to the minimum value (V2-V4). The signal (LA) of the applied voltage to the second liquid crystal cell 63 has a half cycle phase difference from the signal (NA) of the applied voltage to the adjacent first liquid crystal cell 62.

FIG. 5 is a timing chart similar to FIG. 4 when a bright color display is performed using a liquid crystal cell having a normal white characteristic.

(M) is a sync signal for odd and even fields for image display, similar to FIG. 4C shows an analog sample and hold signal corresponding to the video signal voltage supplied to the first picture element electrode 12, which is output from the first video signal supply circuit 5 as in FIG. Due to the color display, the voltage value changes between V5 and V6. (A) is an analog sample hold signal supplied to the second picture element electrode 28, which is output from the second video signal supply circuit 6 and has a half cycle phase difference from the signal (C). (No) and (o)
Is a bias voltage signal of the first counter electrode signal and the second counter electrode signal, and is the same signal as the signal (T) and the signal (N) in FIG. (Ku) and (ya) are the first
This is a signal of an applied voltage applied to the liquid crystal cell 62 and the second liquid crystal cell 63.

The signal supply system is the same as that shown in FIG.
Since the bias voltage signal (No) and the signal (E) are supplied to the 44 and the second counter electrode 52, respectively, the signal (K) of the applied voltage of the first liquid crystal cell 62 = the signal (C) -the signal. (No)
Then, the signal (YA) applied to the second liquid crystal cell 63 = (signal) (I) − (O), the signal (KU) is sent to the first liquid crystal cell 62 and the signal is sent to the second liquid crystal cell 63. (Y) is applied, and changes in the amplitude of (V5-V3) to (V6-V4). Then, the signal (Y) of the voltage applied to the second liquid crystal cell 63
Has a half-cycle phase difference with respect to the signal (H) of the voltage applied to the adjacent first liquid crystal cell 62.

Although the above description has been made only with respect to the signals of the applied voltage of the first liquid crystal cell 62 and the second liquid crystal cell 63, all the first liquid crystal cell columns to which the first video signal is supplied from the first video signal supply circuit 5,
The same applies to all the second liquid crystal cell columns to which the second video signal is supplied from the second video signal supply circuit 6, and the liquid crystal cells adjacent to each other are all supplied with the video signals having a half-cycle phase difference, Further, the first counter electrode row facing the first picture element electrode row of the first liquid crystal cell row and the second counter electrode row facing the second picture element electrode row of the second liquid crystal cell row have a half cycle. Since the first and second counter electrode signals having the phase difference of 1 are respectively supplied, the liquid crystal cell columns adjacent to each other are all driven by the applied voltage having the phase difference of a half cycle.

As described above, the adjacent liquid crystal cells are driven by the driving method of the present invention in which the counter electrode is divided into the first and second counter electrodes and the counter electrodes have a half-cycle phase difference. For example, the applied voltage V of the video signal as shown in FIG. 3 can be varied only between the voltage value Va and the voltage value Vb, and the applied voltage V can be sufficiently close to the voltage value Vb. It is possible to display a high-contrast image without flicker.

Although a liquid crystal cell having a normal white characteristic was used in this example, the contrast effect is the same even when a liquid crystal cell having a normal black characteristic is used, and the TV signal is shown only by applying an NTSC signal. , PAL system (50H
It is also applicable to the signal of z).

(G) Effect of the Invention According to the present invention, it is possible to apply a bias voltage to the counter electrode corresponding to the polarities of the video signals which are inverted with respect to each of the liquid crystal cells of the odd line and the even line of the video signal. Thus, an active matrix type liquid crystal display device that displays a high-contrast image without flicker is provided.

[Brief description of drawings]

FIG. 1 is a partial configuration explanatory view showing a partial configuration of an embodiment of an active matrix type liquid crystal display device of the present invention. FIG. 2 shows the first liquid crystal cell, the second liquid crystal cell, and the third liquid crystal cell.
6 is a timing chart showing the operation of a liquid crystal cell and a fourth liquid crystal cell in interlaced scanning of four liquid crystal cells. FIG. 3 is a graph showing an example of the relationship between the applied voltage (effective value) and the light transmittance of the liquid crystal cell of the normal white characteristic used in this example. FIG. 4 is a timing chart showing applied voltage signals of the first liquid crystal cell and the second liquid crystal cell which are adjacent to each other when dark color display is performed using the liquid crystal cell having the normal white characteristic. FIG. 5 is a timing chart similar to FIG. 4 when a bright color display is performed using a liquid crystal cell having a normal white characteristic. Sixth
FIG. 1 is a partial structural explanatory view of a conventional active matrix type liquid crystal display device. 1,3 ... First video signal line, 2,4 ... Second video signal line, 5 ... First video signal supply circuit, 6 ... Second video signal supply circuit, 7-10 ... Scan line, 11 ... Scan signal supply circuit, 12-19 ... First pixel electrode, 28-35 ... Second pixel electrode, 20-27, 36-43 ... Thin film transistor, 44-51 ... First counter electrode , 52 to 59 ... second counter electrode, 60 ... first counter electrode signal supply circuit, 61 ... second counter electrode signal supply circuit,

Claims (1)

[Claims] 1. A pixel element electrode arranged corresponding to each intersection of a plurality of video signal lines provided in parallel in the vertical direction and a plurality of scanning lines provided in parallel in the horizontal direction, through an active element. In the active matrix type liquid crystal display device which is supplied with a video signal and is interlaced-scanned by the signal from the scanning line, a scanning signal supply means for supplying a signal to the scanning line, and a first odd-numbered column of the video signal line. A first video signal supplying means for supplying a video signal, a second video signal supplying means for supplying a second video signal whose polarity is inverted from that of the first video signal in an even column of the video signal line, and a first video A first signal to which a signal and a second video signal are respectively supplied
And a second pixel electrode, a first counter electrode facing the first pixel electrode, a second counter electrode facing the second pixel electrode, and a first counter electrode signal supplied to the first counter electrode. A liquid crystal comprising: a first counter electrode signal supply means; and a second counter electrode signal supply means for supplying to the second counter electrode a second counter electrode signal whose polarity is inverted from that of the first counter electrode signal. Display device.