JPH03235918A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent a noise from being generated in a fixed pattern owing to the fast polarity inversion of a video signal without increasing the number of picture elements unnecessarily, and to display an image of high quality by driving picture elements with video signals which are different in polarity among the picture elements at random, and change in polarity with time. CONSTITUTION:This display device uses a liquid crystal panel where liquid crystal display elements constituting the picture elements are connected to intersection parts of address lines in a horizontal scanning direction and signal lines in a vertical scanning direction. Then the liquid crystal display device which drives the address lines in sequence and also drives the signal lines drives the signal lines with video signals which are inverted in polarity at random at intervals of one picture element. Namely, a polarity switching circuit 116 is a circuit which inverts the polarities of input R, G, and B signals with an external polarity switching signals and composed of, for example, a complement circuit 131 and an adding circuit 132. Consequently, the noise in the fixed pattern on the screen due to the polarity inversion is reduced to improve the picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a liquid crystal display device that displays images using a liquid crystal panel, and particularly to a drive circuit for a liquid crystal panel.

(Prior Art) Liquid crystal display devices have recently begun to be used in portable liquid crystal TVs because of their low power consumption and thinness. FIG. 13 shows a general configuration of a liquid crystal TV.

In FIG. 13, a video demodulation circuit 1120 demodulates a luminance signal and a color difference signal from a video signal voltage input via a tuner 1100 and a video intermediate frequency amplifier 1110, and further converts it into R, G, and B primary color signals. Ru. The R, G, and B color signals are switched by the color switching circuit 1150 according to the color filter arrangement of each pixel of the liquid crystal panel 1250, and further converted by the polarity switching circuit into signals that are more positive or negative than the reference potential, and then sent to the horizontal drive circuit 1210. is supplied to On the other hand, horizontal and vertical synchronization signals are separated and extracted by the synchronization separation circuit 1130, and from these synchronization signals, the pulse generation circuit 114o generates a clock to be supplied to the vertical scanning circuit 1200, a clock to be supplied to the horizontal drive circuit 121o, and the like.

A specific example of the liquid crystal panel 1220, vertical scanning circuit 1200, and horizontal drive circuit 1210 is shown in FIG. As shown in FIG. 14, the liquid crystal panel 1220 has an intersection between zero address lines 11 extending in the horizontal direction (horizontal scanning direction) and m signal lines 12 extending in the vertical direction (vertical scanning direction). , a liquid crystal display element (hereinafter referred to as pixel) G11. ...+Gmn are arranged in a matrix. Each of these pixels G11. ...1Gmn is
Each has a switching transistor 13 made of TPT (thin film transistor), a capacitor 14, and a liquid crystal cell 15. The vertical scanning circuit 121° outputs gate pulses vvt and VV2 with mutually different output timings.
, vva, -VVN are output to the liquid crystal panel 122o. Horizontal drive circuit 1210 C video signals DO1, DO2
, DO3°...Outputs the DOM to the liquid crystal panel 1220.

As shown in FIG. 15, the horizontal drive circuit 1210 includes an m-stage shift register 1300 and outputs Q1 to Q, 6 of each stage.
It is composed of m sample and hold circuits 1301 and an output buffer (amplifier) 1302 connected to the circuit.

The operations shown in FIGS. 14 and 15 will be explained with reference to the time chart shown in FIG. 16. When the clock pulse CP and data D are input to the shift register 1300 in FIG. 15, sample pulses are output to Q, to Q, n. The sample and hold circuit 1301 samples the input video signal VIN using a sample pulse, and the held signal is applied to the signal line 12 via the output buffer 1302 as the video signal D01-DOM. On the other hand, the vertical scanning circuit 1200 outputs pulses VVI to VVN corresponding to IH (horizontal scanning period). As a result, for example, the transistor 13 in the pixel G11 is turned on, and the video signal 001-D held by the sample and hold circuit 13o1 is turned on.
The voltage of OM is passed through the transistor 13 to the capacitor 14.
is maintained.

The transmittance of the liquid crystal cell 15 in the pixel G1□ changes according to the video signal voltage held in the capacitor 14, and displays a video.

Similarly, the video signal DO2 is sent from the horizontal drive circuit 1210.
, DO3, . . . each time the DOM is sequentially output, a plurality of pixels G, 1 . ... G.

Among them, the output timing of the video signals DO2, 003, . . . DOM and the gate pulses VVI, VV2. ...VV
Pixels corresponding to N output timings operate sequentially. Through the above series of operations, a video corresponding to the input video signal V1N is displayed on the liquid crystal panel 1220.

As is well known, alternating current driving is generally used in such liquid crystal display devices in order to improve reliability and extend life. For example, when displaying television images, a video signal whose polarity is inverted every frame or field is input to the input video signal VI.
Used as N. FIG. 16 shows the waveform of the video signal in which the polarity of the second field is inverted.

In this case, due to the resistance of the switching transistor of each pixel when it is turned off, the jump in gate pulses v1 to VVN, and the interference between surrounding pixels, there is a difference between when a positive polarity video signal is supplied and when a negative polarity video signal is supplied. The effective voltage of the video signal applied to each pixel differs depending on the time. For example, if the polarity is reversed at 80 Hz for each field, a 30 Hz flicker will occur due to the difference between positive and negative effective voltages. 3
Since flicker at 0 Hz is visually very noticeable, in order to remove it, for example, there are methods in which the polarity of the input video signal VIN is inverted at high speed, that is, for each scanning line, a method in which it is inverted for each signal line, and a method in which the polarity is inverted for each pixel. Various methods have also been proposed, such as a method in which the image is reversed. Both methods have a large area (the entire panel)
By replacing the flicker that occurs with lines or dots, it can be visually identified.

Since all of these methods periodically invert the polarity of the video signal, so-called fixed pattern noise occurs in the form of vertical stripes, horizontal stripes, or dots. To prevent this, the number of pixels can be increased and the frequency of these vertical stripes, horizontal stripes, dotted noise, etc. can be increased to make them invisible. However, increasing the number of pixels increases the number of TPTs, lowering the yield of liquid crystal panels, and also decreasing the area (aperture ratio) that actually contributes to display, resulting in a dark screen.

(Problems to be Solved by the Invention) As mentioned above, in conventional liquid crystal display devices, the polarity of the input video signal is periodically changed in order to realize AC drive, which causes fixed pattern noise and If the number of pixels is increased to avoid this noise, there are problems in that the yield of the liquid crystal panel decreases, and the aperture ratio of the liquid crystal panel decreases, resulting in a dark screen.

The present invention has been made in view of the above points, and it is possible to prevent flicker by using AC drive, and also to prevent fixed pattern noise caused by high-speed polarity reversal of video signals without increasing the number of pixels more than necessary. The purpose of the present invention is to provide a liquid crystal display device that can prevent the above problems and display high-quality images.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the liquid crystal display device of the present invention includes a liquid crystal panel configured by arranging a plurality of liquid crystal display elements constituting pixels in a matrix. is characterized in that it is driven by a video signal whose polarity differs randomly between pixels and whose polarity changes over time.

That is, more specifically, a liquid crystal panel is used in which a plurality of liquid crystal display elements constituting pixels are connected to the intersections of a plurality of address lines along the horizontal scanning direction and a plurality of signal lines along the vertical scanning direction. In a liquid crystal display device that sequentially scans multiple address lines and drives multiple signal lines with video signals, the signal lines are driven by video signals whose polarity is randomly reversed in one pixel cycle. be.

(Function) In the present invention, the signal lines of the liquid crystal display panel are AC-driven by video signals with randomly different polarities between each pixel. Flicker is prevented without creating a fixed pattern of noise on the screen that would occur if the polarity was reversed.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a liquid crystal television as a liquid crystal display device according to an embodiment of the present invention. The NTSC composite video signal supplied to the input terminal IN is sent to the A/D converter 1.
After being digitized by 11, frame memory 1
Written to 2. The video signal read from the frame memory 12 is separated into a luminance signal and a color difference signal by a Y-C separation circuit 113. The current NTSC system uses an interlaced system, so the LCD panel 1
In order to facilitate display at 25, the separated luminance signal and color difference signal are converted by a non-interlace conversion circuit 114 into a signal with 535 scanning lines and a frame frequency of 80 Hz. As is well known, this interlace → non-interlace conversion uses scanning line interpolation when there is large movement.
When there is little movement, field interpolation is used. The luminance signal and color difference signal converted by the non-interlace conversion circuit 114 are further converted into RlG, B by an R, G, B conversion circuit 115 configured using a matrix circuit.
converted into a signal.

In order to AC drive the liquid crystal panel 125, the R, G, and B signals are temporally switched between positive and negative polarities by the polarity switching circuit 116, and then converted back to analog signals by the D/A converter 117 before being sent to the horizontal drive circuit. 124.

The polarity switching circuit 116 is a circuit that inverts the polarity of the input R, G, and B signals by a polarity switching signal from the outside.For example, as shown in FIG.
Consists of 2.

On the other hand, synchronization components such as horizontal synchronization, vertical 0 synchronization, and color burst are separated from the input NTSC composite video signal by a synchronization separation circuit 118, and horizontal and vertical timing clocks, etc. are generated by a timing generator 119 based on these synchronization components. The drive pulse generator 120 is created and further uses the timing clock as a reference.
A drive pulse for driving the vertical scanning circuit 123 and the horizontal drive circuit 124 is thereby generated. Drive pulse generator 12
0 supplies, for example, a one-pixel period clock (referred to as a pixel clock) to the random pattern generator 121.

The random pattern generator 121 randomly generates a binary pattern of "1" and "0" in one pixel period in synchronization with this pixel clock, that is, a random pattern, and sends this to the polarity switching circuit 116 as a polarity switching signal. supply

The operation of the polarity switching circuit 116 shown in FIG. 2 will be explained using the timing chart shown in FIG. 3.

A random pattern Q of “1” and “0” generated by the random pattern generator 121 and cycled with the pixel clock CK. is generated and supplied to polarity switching circuit 1 116 as a polarity switching signal. Qo is “0”
If so, the video signal data input to the polarity switching circuit 116 passes through the complement circuit 131 as is and is output.

If Qo is "1", the input video signal data is converted into complement data by the complement circuit 131 and then output. The output signal of the complement circuit 131 is further sent to the adder circuit 11.
6, a constant value is added thereto, the signal is input to the D/A converter 117, and is output as an analog video signal VIN. The purpose of the adder circuit 132 is to apply an offset voltage to the signal line 12 in accordance with the voltage-transmittance characteristic curve of the liquid crystal panel 125. If the voltage-transmittance characteristics of the liquid crystal panel 125 are different between positive polarity and negative polarity, it is desirable to add different values for each polarity to provide the optimum offset voltage. The video signal data input to the polarity switching circuit 116 is a luminance signal in the case of monochrome display, and is an R, G, B signal in the case of color display.

2. In the case of color display, as shown in FIG. 4, three polarity switching circuits 116+ corresponding to R, G, and B signals are used as the polarity switching circuit 116.

Prepare 1162.1163. In this case, the random pattern generator 121 may be used commonly for each of the R, G, and B signals.

Further, as shown in FIG. 5, R
, G, B switching circuit 126 is inserted, and by this R, G, B switching circuit 126, for example, R, G, B signals are transferred to the liquid crystal panel 1.
After switching according to the 25 color arrays, the polarity switching circuit 116
You can also switch the polarity with .

The display video signal v1N obtained as described above is input to the horizontal drive circuit 124 and is applied to the liquid crystal panel 125. FIG. 6 is a specific example of the horizontal drive circuit]24,
FIG. 7 is a timing chart showing the operation. Pulse Q1. generated from shift register 1241 according to CPH pulse and STH pulse. Q2. ...QM
With VIN as a sample pulse, the input video signal VIN is sampled by the sampling transistor 1242 and held by the hold capacitor 1243. Transfer transistor 124 during the horizontal blanking period
4 is turned on by the ST pulse, the charge in the capacitor 1243 is transferred to the output buffer (amplifier) 124.
5 and supplied to the signal line 12 of the liquid crystal panel 25 as video signals DO1, DO2, . . . DOM.

Note that a random pattern generator 1 for generating polarity switching signals
21 includes, for example, a shift register 1211 and an exclusive OR circuit 12 for feedback as shown in FIG.
A known M-sequence (maximum long period code sequence) generator consisting of 12 can be used. In this case, for example, if a 20-stage shift register 1211 is used, a pseudo-random pattern with a period of 1048575 pulses can be generated. It is also possible to control the repetition period of the pseudo-random pattern by resetting the shift register 1211 every few frames or seconds.

4 FIG. 9 shows another example of the random pattern generator 121, in which the shift register 121 is
At the same time as resetting 1, RES is supplied to the flip-flop 1213 to create a pulse that is inverted every frame, and this pulse is used to reset the exclusive OR circuit 1.
214, the output Q of the shift register 1211 is inverted for each frame. In this case, the polarity of the voltage applied to each pixel on the liquid crystal panel 125 is periodically reversed for each frame, but is random between the pixels on the liquid crystal panel 125 according to a pseudo-random pattern.

In the above embodiment, the polarity switching circuit 116 switches the polarity of the input video signal data as it is digital data, but a polarity switching circuit may be provided after the D/A converter 117 in FIG. In that case, as shown in FIG. 10, the output of the D/A converter 117 is input to the positive phase amplifier 1161 and the negative phase amplifier 11B2 to create the positive and negative analog video signals vlN+ and VI□ shown in FIG. and a random pattern Q from the random pattern generator 121. The configuration is such that v and N are created by selectively turning on switches 1163 and 1184 on the output side of amplifiers 1161 and 1162 using as a control signal. Random pattern Q. is directly supplied to the switch 1163 as a control signal, and the inverter 1 is supplied to the switch 1164.
165 and then supplied as a control signal.

As another example, as shown in FIG. 12, positive and negative video signals vIN+ + VIN- are supplied to the horizontal drive circuit 124 to generate a random pattern Q. According to transistor 12
VIN by selectively turning on 42.1248.
, , VIN- may be selectively sampled and held in the hold capacitor 1248.

In addition, the present invention can be modified and implemented without departing from the gist.

[Effects of the Invention] As explained above, according to the present invention, the polarity of the video signal supplied to the signal line of the liquid crystal panel is inverted randomly among the six pixels, that is, randomly within the screen, or even on the time axis. By making the inversion period random, high-speed AC drive to prevent flicker is achieved for each pixel, while noise in fixed patterns on the screen caused by periodic polarity inversion is reduced.
Image quality can be improved.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a liquid crystal display device according to an embodiment of the present invention, Fig. 2 is a block diagram showing a more detailed embodiment of polarity switching in Fig. 1, and Fig. 3 explains the operation of Fig. 2. 4 and 5 are block diagrams showing a specific example of a random polarity switching circuit for RGB signals for color video display, and FIG. 6 is a specific example of the horizontal drive circuit in FIG. 1. 7 is a timing chart for explaining the operation of FIG. 6, and FIGS. 8 and 9 are block diagrams showing specific examples of the random pulse generator.
Figure 0 is a diagram showing a specific example of the polarity switching circuit, and Figure 11 is a diagram showing a specific example of the polarity switching circuit.
07 Timing chart for explaining the operation in Fig. 12
The figure shows an example of a horizontal drive circuit including a polarity switching circuit, and FIG. 13 is a block diagram of a conventional general LCD television.
FIG. 14 is a diagram showing the liquid crystal panel, vertical scanning circuit, and horizontal drive circuit in a conventional liquid crystal display device, FIG. 15 is a diagram showing the conventional horizontal drive circuit in detail, and FIG. 16 is a diagram showing the conventional horizontal drive circuit in detail. It is a timing chart showing the operation. 11...Address line, 12...Signal line, Gll~G
1llfi...pixel (liquid crystal display element), 13...
Switching transistor, 14... Capacitor, 1
5... Liquid crystal cell, 16... Switching transistor, 116... Polarity switching circuit, 121... Random pattern generator, 123... Vertical scanning circuit, 124...
...Horizontal drive circuit, 125...Liquid crystal panel.

Claims (2)

[Claims] (1) A liquid crystal panel configured by arranging a plurality of liquid crystal display elements constituting a pixel in a matrix, and a video signal whose polarity randomly differs between pixels and whose polarity changes over time. 1. A liquid crystal display device comprising driving means. (2) a liquid crystal panel in which a plurality of liquid crystal display elements constituting pixels are respectively connected to intersections between a plurality of address lines along the horizontal scanning direction and a plurality of signal lines along the vertical scanning direction; and the plurality of addresses. A liquid crystal display device comprising: means for sequentially scanning lines; and means for driving the plurality of signal lines with a video signal whose polarity changes randomly in one pixel period.