JPH071621Y2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an active matrix type liquid crystal display device.

(B) Conventional technology In recent years, a portable type liquid crystal television using a liquid crystal matrix panel has been actively developed. For example, the magazine “Nikkei Electronics NO.351” (published on September 10, 1984) No. 211. -The details are introduced on page 240.

FIG. 12 shows an example of an electrode circuit diagram of an active matrix panel using a TFT (thin film transistor) in the liquid crystal television. In FIG. 12, (1), (1), ... Are segment electrodes formed on the first substrate, and (2), (2), ... Corresponding to these segment electrodes (1), (1) ,. Of the TFTs (2) and (2) connected to the corresponding segment electrodes (1) (1). (3) (3) ...
Are TFT lines corresponding to the segment electrodes (1) (1) in the column direction ... (2) (2) ... Drain lines connected to the drains of each column, and (4) (4) ... are the segment in the row direction. TFTs (2) (2) corresponding to electrodes (1) (1) ...
It is a gate line connected to the gate for each row.

On the other hand, (5) is each segment electrode (1) (1) ...
TFT (2) (2) ..., Drain line (3) (3) ...,
A common electrode (counter electrode) formed on a second substrate facing the first substrate on which the gate lines (4) (4) ... Are formed, and liquid crystal is filled between the first and second substrates. There is.

Further, the number of rows, that is, the gate lines (4) (4) ...
The number of scanning lines is 240, and the number of scanning lines per field in NTSC is 2
This is roughly equivalent to the number of effective scanning lines out of 62.5.

Therefore, when driving, all 250 lines are used in each of the odd field and the even field, and the same element is driven again after 1/60 seconds.

A video signal is applied to the drain lines (3), (3) ... Of the active matrix panel. Normally, when driving the liquid crystal, AC driving is performed in consideration of durability thereof, that is, at a predetermined cycle. It is preferable to invert the polarity of the signal, and the video signal is as shown in FIG. 13, for example.

That is, if the nth of the odd field is O _n and the _{nth of} the even field is E _n , the odd field (01) (02)
Has a positive polarity and even fields (E1) and (E2) have a negative polarity, so that the polarities are inverted for each field.

Therefore, the cycle in which the same element is driven with the same polarity is 1/30 second, that is, one frame cycle. Therefore, flicker (flickering) on the screen due to polarity reversal is almost invisible.

However, in the above conventional example, the number of rows is 240,
It has a drawback that the screen has a relatively low resolution with a small number of pixels.

Therefore, the number of rows is set to 480 and the number of pixels is increased,
A method for improving image quality has been proposed.

FIG. 14 shows an electrode circuit diagram of the active matrix panel in the second conventional example. The same parts as those in FIG. 12 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 14, there are 480 gate lines (41) (42) ... Which are drawn out to the left and right for each row, and a gate signal is applied to the gate lines (41) ... 42) ... A gate signal is applied to every even field.

The polarities of the video signals applied to the drain lines (3), (3), ... Of the active matrix panel are inverted every two fields as shown in FIG. 1/15 seconds, or 2 frame cycles.

Therefore, the flicker on the screen due to the polarity reversal has a low frequency and is very noticeable.

When the LCD panel (1) is viewed from the front, the flicker occurs in one frame cycle as shown in FIG. 16 (b) with respect to the drive waveform of two frame cycles shown in FIG. 16 (a). However, when the LCD panel (1) is viewed obliquely, for example, when it is displaced from the front by 10 °, the brightness is reduced as shown in FIG. It will be.

(C) Problems to be solved by the present invention The present invention has been made in view of eliminating the above-mentioned drawbacks of the conventional example, and the number of rows of the color matrix display device is increased from 240 to 480, for example. An object of the present invention is to make flicker on the screen inconspicuous due to AC driving of liquid crystal even when the number of pixels is increased and resolution is improved.

(D) Means for Solving the Problems The liquid crystal display device of the present invention is an active matrix type and has a counter electrode facing a pixel electrode of a display pixel unit extended in a row and in a column direction so as to intersect diagonally. This is divided into a suitable number of rows and a suitable number of columns, and the polarity of the video signal applied to each display pixel electrode is inverted at a predetermined cycle and the voltage of each applied DC voltage independent between each divided counter electrode. It is characterized in that the value is switched and set between a first value and a second value in a predetermined cycle.

(E) Action The present invention can reverse the polarity of the video signal to be applied at least for each one or a plurality of display pixels adjacent in the same column (vertical direction) and in the same row (horizontal direction). The flicker of the entire screen is visually compensated by the above means.

Further, the present invention is such that the polarity of the video signal is inverted every one horizontal scanning period or a plurality of horizontal scanning periods, and the above-mentioned means make the brightness of each part on the screen uniform and prevent horizontal stripes. can do.

Further, the present invention provides a liquid crystal panel in which a plurality of display elements are arranged in a matrix, a polarity inversion circuit that inverts the polarity of a video signal applied to the liquid crystal panel for each field, and a counter electrode of the liquid crystal panel for each field. A liquid crystal display comprising a circuit for supplying a selected first or second DC voltage and a brightness level adjusting circuit for simultaneously changing the first and second DC voltages in opposite directions to adjust the brightness level of the video signal. The device can be realized.

(F) Example First, FIGS. 1 and 2 show an example of a driving method adopted in a liquid crystal display device.

FIG. 1 is a block diagram of the circuit of this embodiment.
LCD panel (10), first and second column drive units (20), (3
0), first and second row drive units (40), (50), first and second
It is composed of polarity inversion circuits (60) and (70) and a synchronization control circuit (80).

The LCD panel (10) is an active matrix panel of 480 rows with mosaic color filters facing each other, and color unit display elements such as G, R, B are arranged in order horizontally from the upper left. ing.

The first and second column drive units (20) and (30) are synchronous control circuits (8
0) generate the clock pulse (CP) and the first start pulse (ST ₁ ) respectively, the first and second shift registers (21) and (31), and the output pulse of each digit of this shift register is a sampling pulse. The first and second sample and hold circuits (22) for sampling the video signal output of the first or second polarity inversion circuit (60), (70) and holding for one horizontal scanning period by the horizontal synchronizing pulse (HP). ), (32), the pixels in odd columns are driven by the output of the first sample and hold circuit, and the pixels in even columns are driven by the output of the second sample and hold circuit.

The first row driving unit (40) outputs a second start pulse (S) generated by the synchronization control circuit (80) at the start of an odd field.
T ₂ ) is a data input and a horizontal synchronizing pulse (HP) is a clock input, and the shift register is configured to output the respective digit outputs to drive the respective odd-numbered gate lines. The second row driving section (50) receives the third start pulse (ST ₃ ) generated at the start of the even field as the data input and outputs the horizontal sync pulse (H
P) is a clock input
Each digit output drives an even number of gate lines.

The first polarity reversing circuit (60) reverses the polarity of the video signal frame by frame according to the control signal from the synchronization control circuit (80) and supplies it to the first sample hold circuit (22).

The output of the first polarity inverting circuit (60) is further inverted by the second polarity inverting circuit (70) for the entire period, and the inverted output is supplied to the second sample hold circuit (32).

Therefore, the signals applied to horizontally adjacent pixels on the LCD panel (10) have opposite polarities.

Furthermore, the synchronization control circuit (80) has a built-in PLL circuit,
Synchronized with the first start pulse (ST ₁ ) synchronized with the horizontal sync pulse (HP), the vertical sync pulse (VP), and the second start pulse (ST ₂ ) generated at the start of the odd number field with the vertical sync pulse (VP) However, the third start pulse (ST ₃ ) generated at the start of the even field and the PLL circuit
Create a clock pulse (CP) that is the divided output of the VCO.

According to the drive circuit described above, horizontally adjacent pixels are driven by video signals of opposite polarities. Therefore, flicker due to AC driving of the adjacent pixels is visually offset from each other, and the flicker of each pixel is 2%. Even if the frame period and the low frequency are set, the flicker of the entire screen hardly occurs.

Further, FIG. 2 is a waveform diagram for explaining flicker when the LCD panel (10) is viewed from a direction deviated from the front by 10 °,
2 (a) to 2 (d) show driving waveforms applied to the pixels on the LCD panel (10), respectively, and FIG.
(H) indicate the brightness of each pixel. In this case, 4
Flicker occurs in each of the 2 pixels per frame,
When the four pixels are regarded as one as a whole, the visual luminance in FIG. 2 (i) is a combination of the luminances of the respective pixels, and the flicker period becomes one field and the frequency increases, Flicker is virtually unnoticeable.

Incidentally, in the above-mentioned driving method, the polarity of each one pixel adjacent in at least the same row is inverted, but the polarity may be inverted every plural adjacent pixels.

According to the driving method as described above, in a liquid crystal display device in which a video signal whose polarity is inverted at a predetermined cycle is applied to a liquid crystal panel in which a plurality of display pixels are arranged in a matrix, at least one or a plurality of adjacent display pixels in the same row are provided. For each of the display pixels of
By newly providing a liquid crystal display device characterized by inverting the polarity of the video signal to be applied, the number of rows of a color LCD panel is set to, for example, 500, and low frequency is applied to each pixel by driving in an interlace system. Even if the flicker occurs, the flicker does not appear visually on the entire screen.

Also, when viewing a color LCD panel from an angle,
Even if the frequency of the flicker of a pixel is lower than that when viewed from the front, the flicker can be visually compensated.

Another driving method is shown in FIGS. 3, 2, and 4.

FIG. 3 is a block diagram of the drive circuit. The LCD panel (1
0), first and second column driving units (20) and (30), first and second row driving units (40) and (50), first and second polarity reversing circuits (60),
(70) and each circuit configuration of the synchronization control circuit (80) are exactly the same as those in FIG. 1, and their explanations are omitted.

This embodiment is different from the first embodiment in that the first polarity reversing circuit (60) reverses the polarity of the video signal for each frame in response to the control signal from the synchronization control circuit (80), and the first horizontal scanning period (1H ) Is also the point that the polarity can be reversed. Second
3A to 3D show drive waveforms applied to each pixel of FIG. 3, and FIGS. 2E to 3H show the luminance of each pixel. As in the case of the driving method described above, even in the driving method of the present embodiment, flicker occurs in each of the four pixels in a two-frame cycle, but if the four pixels are regarded as one as a whole, Visual brightness FIG. 2 (i) is a composite of the brightness of each pixel, and the flicker period becomes one field, and the frequency increases, and the flicker becomes substantially inconspicuous.

FIG. 4 is another waveform diagram showing the operation of the drive circuit shown in FIG. In FIG. 4, V _v is a video signal whose polarity is inverted every 1H and every frame, VG ₁ , VG ₂ ... VGN is a gate electrode line (G) of each row corresponding to an odd field.
The gate signals applied to (G) ..., VP ₁ , VP ₂ ... VPN are voltages held by the liquid crystal in each row corresponding to the odd fields.

First, in the odd field, the video signal (V _v ) sampled at the high timing of the gate signal (VG ₁ ) at 1H.
Voltage is applied to the liquid crystal and the gate signal goes low, and then it is going to be held for one frame period. Actually, as described above, the source electrode line is charged and discharged through the off resistance of the TFT and held. The voltage becomes like VP ₁ . The amount of charging / discharging in one frame depends on the voltage of the video signal of the source electrode line, but since the video signal is inverted every 1H, the average voltage of the source electrode line in one frame is The parts are almost the same. Therefore,
Each of the holding voltages VP ₁ , VP _2, ... VPN has the same charge / discharge amount as illustrated. This also applies to even fields. At this time, it should be noted that the video signal has a polarity opposite to that of the previous time when the same pixel is driven one frame later.

Therefore, uneven brightness does not occur at the top and bottom of the screen.

Further, since pixels adjacent to each other in the horizontal direction are driven by video signals having polarities opposite to each other, the flicker caused by the AC driving of the adjacent pixels is visually canceled each other, and the flicker of each pixel is 2 frame periods and low frequency. However, there is almost no flicker on the entire screen.

Although the polarity of the video signal is inverted every 1H in the above embodiment, it may be inverted every several H. Further, the polarity may be inverted for each of a plurality of adjacent pixels.

According to the driving method described above, in a liquid crystal display device in which a video signal whose polarity is inverted at a predetermined cycle is applied to a liquid crystal panel in which a plurality of display pixels are arranged in a matrix, one horizontal scanning period or a plurality of horizontal scanning periods is performed. In addition, a new liquid crystal display device characterized by reversing the polarity of the video signal is provided to lower the brightness at the bottom of the screen, or to reduce the brightness of even lines compared to odd lines in the interlace method. It is possible to obtain a substantially uniform brightness in any part of the screen.

FIG. 5 is a circuit diagram of a liquid crystal display device adopting the above-mentioned driving method. In the figure, (10) is a well-known active matrix type liquid crystal panel, (T) is a TFT (thin film transistor), and (LC) is a liquid crystal panel. Represents a liquid crystal. Reference numeral (20) is a Y driver which drives each drain line (D) (D) of the TFT (T) including a shift register and a sample hold circuit, and samples a video signal at a predetermined sampling clock. (40) is composed of a shift register
An X driver for driving each gate line (G) (G) of (T) (T) ..., One bit of data is set by a vertical synchronizing signal, and a predetermined gate line is sequentially shifted by a horizontal synchronizing signal. The signal selected and held by the Y driver is supplied to TFT (T) (T).

(100) is a T-flip-flop (T-FF) whose outputs are inverted every clock input (vertical synchronization signal), (S ₁ ) (S ₂ )
(S ₃ ) and (S ₄ ) are the Q output of the T-FE and the first, second, third, fourth, and analog switches controlled by the output. (110) is a brightness level adjusting circuit, which is composed of a first resistor (R ₁ ), a variable resistor (VR) and a second resistor (R ₂ ) connected in series between the direct current (+ V _DD ) and the ground. , The connection point (first connection point) (P ₁ ) between the first resistance (R ₁ ) and the variable resistance (VR) is the first analog switch (S ₁ )
In addition, the connection point of the variable resistor (VR) and the second resistor (R ₂ ) (second
The connection point) (P ₂ ) is connected to the second analog switch (S ₂ ). The first and second analog switch outputs are connected to the counter electrode line (90) of the liquid crystal (LC) (LC) ... And the third and fourth analog switch outputs are connected to the counter electrode line (91). There is. Reference numeral (60) is a polarity inversion circuit that inverts the polarity of the video signal in a field cycle by a control signal such as a vertical synchronizing signal.

Next, the operation of the above circuit will be described.

First, since the T-FF100 output is inverted at the field period, for example, the first and fourth analog switches (S ₁ ) (S ₄ ) are turned on at odd field, off at even field, second, third.
The analog switches (S ₂ ) (S ₃ ) are opened / closed so that they are off during odd field and on during even field. Therefore, as shown in FIG. 5, in the odd-numbered field, the high voltage (VH) of the first connection point (P ₁ ) of the brightness level adjusting circuit 110 is applied to the opposite electrode line (90) and the second connection point (P _2). ) Is applied to the counter electrode line (91), and the voltage (VL) is applied to the line (90) in the even field.
Then, a voltage (VH) is applied to line (91).

On the other hand, the video signal is inverted by the polarity inversion circuit (6) in the field cycle, and its level is set between VH and VL as shown in FIG.

Then, when changing the brightness level, for example, when increasing the brightness, it suffices to adjust so that the resistance value of the variable resistor (VR) becomes large, that is, the voltage (VH) at the first connection point (P ₁ ) is higher. Since the voltage becomes higher and the voltage (VL) at the second connection point (P ₂ ) becomes lower, the voltage between the counter electrode level and the video signal level becomes large in FIG. 11 and the brightness becomes high.

The above-mentioned circuit of FIG. 5 is for line switching, but as a modification of FIG. 5, FIG. 6 shows full line line switching, and the same operation as in FIG. It can be effective.

Further, FIG. 7 shows a circuit for realizing driving of dot switching in the horizontal direction, and FIG. 8 shows a driving circuit for line switching and dot switching in the vertical direction. In the case of FIG. 7, only the line switching in the vertical direction of FIG. 5 is changed to the dot switching in the horizontal direction, and a flicker compensation effect similar to that of the system of FIG. In this case, the flicker compensation effect obtained by synergizing the effect of FIG. 5 with that of FIG. 7 can be obtained. Further, FIG. 9 shows a case where both line and dot are switched in full line, and as in FIG. 8, high flicker compensation effect is exhibited.

FIG. 10 shows a specific example of the electrode arrangement in the panel structure of the liquid crystal display device of the present invention. The electrode arrangement shown in the figure corresponds to the circuit of the embodiment shown in FIG. The panel (P) in the figure has a liquid crystal material interposed between a first substrate (for example, a glass substrate) and a second substrate (for example, a glass substrate), and a TFT (not shown) is provided on the first glass substrate. No.) are segment electrodes (1), (1), ... On the other hand, the counter electrode of the second substrate facing it is in a direction intersecting both the gate line direction and the drain line direction of the display pixel at an angle of about 45 °, that is, in the right oblique downward direction intersecting the row direction and the column direction of the segment electrodes. It is composed of a plurality of diagonally divided counter electrodes (51) (52) (51) (52) ... Divided into one row and one column so as to extend, and has odd diagonal rows and diagonally divided counter electrodes (51) (51). ... are connected to each other and diagonally divided counter electrodes (52) (52) in even diagonal rows ...
Are also connected to each other.

As shown in the circuit configuration of FIG. 8 and the signal waveform diagram of FIG. 11, a video signal whose polarity is inverted in the field cycle is applied to the segment electrodes (1) (1) ... The first DC voltage VL and the second DC voltage VH are alternately switched and applied to the diagonally divided counter electrodes (51), (51) ... 52) is applied with a voltage in the opposite phase to that of the odd diagonal row.

(G) Effect of the Invention According to the present invention, in an active matrix type liquid crystal display device in which a plurality of display pixels are arranged in a matrix, the counter electrode facing the pixel electrode of each display pixel unit is divided into a proper number of diagonal rows. The polarity of the video signal applied to each display pixel electrode is inverted in a predetermined cycle, and the voltage values of the respective applied constant voltages independent between adjacent division-corresponding electrodes are set to a first value and a second value in a predetermined cycle. It is possible to invert the polarity of the video signal to be applied for each one or a plurality of display pixels adjacent in the same column and in the same row because the setting is switched between the values of It is possible to compensate for flicker. In addition, since the brightness of the video signal can be adjusted extremely easily and the power consumption of the power supply voltage can be reduced, it is possible to configure a liquid crystal display device which is easy to see even if the ambient brightness changes.

[Brief description of drawings]

FIG. 1 is a block diagram of a drive circuit that can be adopted in a liquid crystal display device, FIG. 2 is a waveform diagram of a main part of FIG. 1, FIG. 3 is a block diagram of a drive circuit of another liquid crystal display device, and FIG. Is the second
FIG. 5 is a waveform diagram in the main part of the figure, FIG. 5 is a circuit diagram of a drive circuit of a liquid crystal display device according to the present invention, FIG. 6, FIG. 7, FIG.
And FIG. 9 are circuit diagrams showing a modification of the circuit of FIG. 5, respectively.
FIG. 10 is a plan view showing a specific example of the electrode arrangement in the panel of the liquid crystal display device of the present invention, and FIG. 11 is a waveform diagram showing the relationship between the counter electrode potential and the video signal in the circuit of FIG.
FIG. 12 is an electrode circuit diagram of a conventional 240-row active matrix panel, FIG. 13 is a waveform diagram of a video signal applied to the panel of FIG. 9, and FIG. 14 is an electrode circuit diagram of a conventional 480-row active matrix panel. FIG. 15 is a waveform diagram of a video signal applied to the panel of FIG. 11, and FIGS. 16A to 16C are waveform diagrams for explaining flicker. (1) ... Segment electrode, (10) ... LCD panel, (2
0), (30) ... First and second row drive units, (40), (50) ...
1, second row drive section, (51), (52) ... diagonally divided counter electrodes,
(60), (70) ... First and second polarity reversing circuits, (80) ... Synchronous control circuit.

Claims (1)

[Scope of utility model registration request] 1. A first array of a plurality of display pixel electrodes arranged in a matrix.
In a liquid crystal display device of an active matrix type in which a liquid crystal material is interposed between a second substrate and a second substrate having a counter electrode facing the substrate, the counter electrodes are arranged in rows and columns. Are divided into a suitable number of rows and a suitable number of columns by extending so as to cross each other diagonally, and the polarity of the video signal applied to each display pixel electrode is inverted with respect to the divided counter electrode at a predetermined cycle and is adjacent. It is characterized in that the voltage value of each applied DC voltage independent between the divided counter electrodes is set to be switched between a first value and a second value within a predetermined period and within a variation range of the video signal before inversion. Liquid crystal display device.