JPH07199153A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To embody a picture display device which can reduce a phenomenon of flicker. CONSTITUTION:This device is provided with a controller 15 in which a polarity inversion control signal is generated based on an odd numbered field and an even numbered field discriminated by a synchronizing processing circuit 14 and this polarity inversion control signal is outputted to polarity inversion circuits 41, 43 as it is, while an inversion signal of a polarity inversion control signal is outputted to a polarity inversion circuit 42 through an inverter 40, and polarity inversion circuits 41, 42, 43 which reverse polarity of R, G, B signals so that a phase of a polarity inversion signal supplied to a source driver of a G liquid crystal panel 32 out of three liquid crystal panels of a R liquid crystal panel 31, G liquid crystal panel 32 and B liquid crystal panel 33 is opposite to a phase of a polarity inversion signal supplied to source drivers of the other R, B liquid crystal panels 31, 33. A phase of alternating current driving signal which drives a liquid crystal panel of at least one color out of three liquid crystal panels for R, G, B 31, 32, 33 is shifted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device used in a liquid crystal projector, a liquid crystal television, etc., and more particularly to a liquid crystal display device using a TFT active matrix panel.

[0002]

2. Description of the Related Art Light from one light source is converted into an R (red) component,
The light is decomposed into three lights of G (green) component and B (blue) component, and the corresponding three liquid crystal display modules are irradiated respectively, and each liquid crystal display module is decomposed into three colors of R, G, B and displayed. There is a liquid crystal projector in which a color image such as a television image thus generated is combined by reflection and transmission and enlarged and projected on a screen by one projection lens.

In this liquid crystal projector, three liquid crystal display modules R, G and B are arranged between a light source and a projection lens, and light from the light source is converted into R by two dichroic mirrors and one reflection mirror. , G, B 3
R, G, and B that have been separated into the colors and radiated to the back surface of the corresponding liquid crystal display module and passed through each liquid crystal display module
The image components of the respective colors are combined by two dichroic mirrors, one reflection mirror, and the like, and are made incident on the projection lens and guided to the screen.

The liquid crystal panel acts as a light modulator for generating an image, and a TFT active matrix panel can reproduce a high quality display image.

FIG. 8 is a circuit diagram of a video signal processing section of such a TFT 3-plate color liquid crystal projector.

In FIG. 8, the video signal processing unit is
C separation circuit 11, color demodulation circuit 12, polarity inversion circuit 13,
It is composed of a synchronization processing circuit 14 and a controller 15.

The Y / C separation circuit 11 is a circuit for separating a composite video signal into a luminance signal Y and a chroma signal C.

The color demodulation circuit 12 has a luminance signal Y and chroma signals C to R separated by the Y / C separation circuit 11,
This is a circuit that creates G and B primary color signals.

The polarity reversing circuit 13 is a circuit for reversing the polarity every predetermined period in order to drive the liquid crystal with an alternating waveform.

The synchronization processing circuit 14 is a circuit for outputting a sync signal for controlling the timing of the controller 16 from the composite video signal (composite video signal), and specifically, a vertical sync signal and a horizontal sync signal from the composite video signal. It separates and transmits to the controller 16.

The controller 15 outputs other control signals to the source driver and the gate driver based on the synchronizing signal input from the synchronizing processing circuit 14 and controls these drivers and the entire apparatus.

The controller 15 outputs a polarity inversion control signal to the polarity inversion circuit 13 based on the odd field and the even field determined by the synchronization processing circuit 14,
The polarity of each R, G, B signal is inverted for driving, and other control signals are output to each section.

When a video signal is input to the video signal processing section of the liquid crystal projector, the video signal is input to the Y / C separation circuit 11 and the synchronization processing circuit 14, and the Y / C separation circuit 11 outputs the composite video signal. The color demodulation circuit 12 separates the luminance signal Y and the chroma signal C into R and R from the luminance signal Y and the chroma signal C separated by the Y / C separation circuit 11.
G and B primary color signals are created and output to the polarity reversing circuit 13.

The polarity reversing circuit 13 includes a controller 15
A polarity inversion control signal is supplied from the color inversion circuit 13 and the polarity inversion circuit 13 inverts the polarity of the R, G, B signals output from the color demodulation circuit 12 in each field according to the polarity inversion control signal. Output to each source driver. Each of R, G, and B source drivers (not shown) displays the input video signal on the three R, G, and B liquid crystal panels.

The driving method of the TFT-LCD is as follows.

FIG. 9 is a timing chart of signal waveforms for driving the TFT-LCD, showing a signal waveform for a certain color.

In FIG. 9, VG and VID are signals of the scanning line and the signal line, which are applied to the gate and the source of the TFT. An NTSC video signal is composed of two interlaced fields, and the first field and the second field are combined into one frame to form one picture.

During the selection period T1, when the TFT is turned on, the pixel electrode potential VP becomes equal to the signal line potential VID.
In the selection period T2, the TFT is turned off and the signals written in the liquid crystal capacitance and the holding capacitance are held, but the pixel electrode potential VP is shifted by a certain voltage ΔV at the moment when the TFT is turned off. This is due to the parasitic capacitance between the gate and drain of the TFT and the capacitive coupling between the liquid crystal capacitance and the storage capacitance.

Since this shift voltage always lowers the pixel electrode potential VP regardless of the polarity of the video signal, the common electrode potential VCOM on the color filter side is set lower than the center potential VC of the signal line by this shift amount. To do. As a result, the voltage VLC applied to the liquid crystal becomes a region shown by the hatched portion in FIG.

[0020]

However, in reality, since the liquid crystal has anisotropy of dielectric constant, the liquid crystal capacitance changes depending on the amplitude of the video signal, and the shift voltage ΔV also changes. Therefore, even if the common electrode potential VCOM is optimized, the voltage VLC applied to the liquid crystal cannot have a completely symmetrical waveform. The resulting asymmetrical component becomes an optical component and is recognized as flicker (flicker on the screen).

In the case of the above-mentioned TFT 3-plate type color liquid crystal projector, there is a problem that flicker appears as in the case of a single-panel TFT panel. Especially 3 T
There is a problem that flicker is amplified and felt because one picture is synthesized by synthesizing the images of the FT panel.

Therefore, an object of the present invention is to provide an image display device using a plurality of liquid crystal display panels, which can reduce the flicker phenomenon.

[0023]

The invention according to claim 1 is
In order to achieve the above object, in a plurality of liquid crystal panels and a liquid crystal display device that AC-drives the plurality of liquid crystal panels to synthesize and display an image, at least one of the plurality of liquid crystal panels is provided.
The phases of the AC drive waveforms of the two liquid crystal panels are shifted.

According to a second aspect of the present invention, in a plurality of liquid crystal panels and a liquid crystal display device for alternatingly driving the plurality of liquid crystal panels to display an image, at least one liquid crystal panel of the plurality of liquid crystal panels is provided. The phase of the AC drive waveform is reversed.

According to a third aspect of the present invention, in a plurality of liquid crystal panels and a liquid crystal display device in which the plurality of liquid crystal panels are AC-driven to synthesize and display an image, a phase of a voltage for AC-driving the plurality of liquid crystal panels is changed. , The liquid crystal panels are displaced from each other.

The plurality of liquid crystal panels may be, for example, as defined in claim 4.
It may be three liquid crystal panels for R, G, and B as described in 1.

The plurality of liquid crystal panels are, for example, as defined in claim 5.
As described in [3], the phase of the AC drive waveform of the three liquid crystal panels for R, G, and B, and the liquid crystal panel for G among the three liquid crystal panels for R, G, and B is reversed. ing.

In the liquid crystal display device, for example, as described in claim 6, the images generated on the three liquid crystal panels for R, G and B are combined by reflection and transmission, and enlarged and projected on the screen. It may be a liquid crystal projector that operates.

[0029]

According to the inventions of claims 1, 2, 3, 4, 5 and 6,
The phase of the AC drive waveform of at least one of the plurality of liquid crystal panels is shifted. For example, R, G, B
The polarity inversion signal supplied to the source driver of one liquid crystal panel among the three liquid crystal panels for use is shifted by 180 ° from the polarity inversion signal supplied to the source drivers of the other two liquid crystal panels. Is composed of.

Therefore, the flicker phenomenon can be alleviated when the images of the three liquid crystal panels are combined.

[0031]

EXAMPLES Examples will be described below with reference to FIGS.

1 to 7 are views showing an embodiment of a liquid crystal display device, and this embodiment is an example in which the liquid crystal display device is applied to a TFT 3 plate type color liquid crystal projector.

FIG. 1 is a block diagram of the optical system of a liquid crystal projector. 1, the liquid crystal projector includes a metal halide lamp 21, a reflector 22, a reflection mirror 23,
24, 25, dichroic mirrors 26, 27, 28,
29, heat ray / ultraviolet ray cut filter 30, liquid crystal panels 31, 32, 33, condenser lenses 34, 35, 3
6 and the projection lens 37.

The metal halide lamp 21 is provided at the focal position of the reflector 22 by the parabolic surface, and the light from the metal halide lamp 21 is reflected by the reflector 22 and is incident on the reflection mirror 23 provided in the lower part of FIG. It The light incident on the reflection mirror 23 is incident on the dichroic mirror 26 for color separation through the heat ray / ultraviolet cut filter 30, and the dichroic mirror 26 reflects only the B component light and transmits other light.
The B component light split by the dichroic mirror 26 is reflected by the reflection mirror 24 and is incident on the condenser lens 36. The condenser lens 36 narrows the light and enters the liquid crystal panel 33.

The light transmitted through the dichroic mirror 26 is incident on the color separation dichroic mirror 27, and the dichroic mirror 27 reflects only the G component light and transmits other light. The G component light split by the dichroic mirror 27 enters the condenser lens 35, and the condenser lens 35 narrows the light to enter the liquid crystal panel 32. The G component light transmitted through the liquid crystal panel 32 is incident on the color combining dichroic mirror 28, and is combined with the B component light transmitted through the liquid crystal panel 33.

Similarly, the light of the R component transmitted through the dichroic mirror 27 is made incident on the condenser lens 34, narrowed down by the condenser lens 34 and made incident on the liquid crystal panel 31. The R component light transmitted through the liquid crystal panel 31 is reflected by the reflection mirror 25 and is incident on the color combining dichroic mirror 29, where the B component light and the G component are combined by the color combining dichroic mirror 28. Further combined with the light of. The light combined by the dichroic mirror 29 is projected onto the screen by the projection lens 37.

As described above, the respective lights dispersed in the order of B, G and R are incident on the liquid crystal panels 31, 32 and 33, and the images corresponding to the respective colors are reproduced on the respective liquid crystal panels 31, 32 and 33. The incident light is modulated by each liquid crystal panel 31, 32, 33 for each color.

In this embodiment, each of the liquid crystal panels 31, 3 described above is used.
The driving method for driving the motors 2 and 33 has the following features.

FIG. 2 is a circuit diagram of the video signal processing unit of the TFT3 plate type color liquid crystal projector, and the same components as those of the conventional video signal processing unit shown in FIG. 6 are designated by the same reference numerals.

In FIG. 2, the video signal processing unit is
C separation circuit 11, color demodulation circuit 12, polarity inversion circuit 41,
42, 43, LCD driver circuits 44, 45, 46, a synchronization processing circuit 14, a controller 15, and an inverter 40.

The LCD driver circuit 44 comprises an R liquid crystal panel 31, a horizontal source driver 47, and a vertical gate driver 48.
Is driven by the source driver 47, the gate driver 48, and the controller 15 that controls these drivers. Similarly, the LCD driver circuit 45 includes a G liquid crystal panel 32, a horizontal source driver 49, and a vertical gate driver 50. The LCD driver circuit 46 includes a B liquid crystal panel 33, a horizontal source driver 51, and a vertical gate driver 50. The G liquid crystal panel 32 and the B liquid crystal panel 33 are driven by the source drivers 49 and 51, the gate drivers 50 and 52, and the controller 15 which controls these drivers for display drive.

The Y / C separation circuit 11 is a circuit for separating a composite video signal into a luminance signal Y and a chroma signal C.

The color demodulation circuit 12 is a Y / C separation circuit 1
1 is a circuit for creating primary color signals of R, G, B from the luminance signal Y and the chroma signal C separated by 1. The created primary color signals of R, G, B are respectively polarity inversion circuits 41,
It is output to 42 and 43.

The polarity reversing circuits 41, 42 and 43 are circuits for reversing the polarities of the R, G and B signals every predetermined period (for example, one field) in order to drive the liquid crystal with an AC waveform. And there are the following differences. That is, the polarity reversing circuits 41, 42 and 43 are used for the R liquid crystal panel 3
The signals (R
', G', B'signals) are output.

In this case, of the three liquid crystal panels of the R liquid crystal panel 31, the G liquid crystal panel 32 and the B liquid crystal panel 33, the polarity inversion signal supplied to the source driver of one liquid crystal panel is the other two liquid crystal panels. The phase is shifted by 180 ° with respect to the polarity inversion signal supplied to the source driver of the panel. In the present embodiment, when the polarities of the R, G and B signals are inverted every one field, only the G signal is shifted by 180 ° with respect to the R and B signals and output to the source drivers 47, 49 and 51. .

The synchronization processing circuit 14 is a circuit for discriminating an odd field and an even field from the composite video signal in order to drive by inverting the polarity of the video signal for each field.

The controller 15 is the synchronization processing circuit 1
A polarity inversion control signal is generated based on the odd field and the even field discriminated by 4, and this polarity inversion control signal is output to the polarity inversion circuits 41 and 43 as it is, and the polarity inversion circuit 42 is passed through the inverter 40. An inverted signal of the polarity inversion control signal is output. Further, the controller 15 outputs other control signals to each unit. Other control signals include, for example, gate drivers 48 and 5
There is a gate drive signal output to 0,52.

The polarity inversion control signal is the polarity inversion circuits 41, 4
3, the output of the inverter 40 of the polarity inversion control signal is supplied to the polarity inversion circuit 42, so that the controller 15 drives the polarity inversion circuits 41 and 43 by inverting the polarity for each R and B signal field. Also, the polarity reversing circuit 42 is driven by reversing the phase by 180 ° with respect to the R and B signals and reversing the polarity for each G signal field.

Next, the operation of this embodiment will be described.

When a video signal is input to the video signal processing section of the liquid crystal projector shown in FIG. 2, the video signal is Y /
It is input to the C separation circuit 11 and the synchronization processing circuit 14, and Y /
The C separation circuit 11 separates the input composite video signal into a luminance signal Y and a chroma signal C (RY, BY) and outputs it to the color demodulation circuit 12.

In the color demodulation circuit 12, the Y / C separation circuit 11
The luminance signal Y and the chroma signals C to R separated by
G and B primary color signals are created and output to the polarity inversion circuits 41, 42 and 43 for each R, G and B signal.

On the other hand, a part of the input composite video signal is input to the synchronization processing circuit 14, and the synchronization processing circuit 14
Discriminates an odd field and an even field from the input composite video signal, and the discriminant result is determined by the controller 1
Output to 5. The controller 15 includes the synchronization processing circuit 14
A polarity inversion control signal is generated based on the odd field and the even field discriminated by, and the polarity inversion control signal is output to the polarity inversion circuits 41 and 43 as it is, and the polarity is inverted to the polarity inversion circuit 42 via the inverter 40. The inverted signal of the control signal is output.

A polarity inversion control signal is supplied from the controller 15 to the polarity inversion circuits 41 and 43, and the polarity inversion circuits 41 and 43 output the R and B signals output from the color demodulation circuit 12 in accordance with the polarity inversion control signal. A signal (R ',
B ′ signal) as R and B source drivers 47, 51
Output to.

Further, the polarity reversing circuit 42 is supplied with the reversal signal of the polarity reversing control signal from the controller 15, and the polarity reversing circuit 42 outputs the G signal output from the color demodulation circuit 12 in accordance with the reversal signal of the polarity reversing control signal. Is inverted every one field and output to the G source driver 49. Here, since the polarity reversal circuit 42 is supplied with an inversion signal of the polarity reversal control signal from the inverter 40, the polarity reversal circuit 42 is 180 ° out of phase with the R and B signals, and in every G signal one field. A signal (G ′ signal) with the polarity inverted will be output.

That is, when inverting the polarities of the R, G, and B signals for each field, the phase of only the G signal is shifted by 180 ° with respect to the R and B signals (in other words, only the G signal has the opposite polarity. ) Output to the source drivers 47, 49, 51.

In this case, the reason why the phase is to be shifted is the G signal because the G (green) component has the greatest effect on the visual sense.

Then, as shown in the waveform diagram of the primary color signal and the polarity inversion control signal in FIG.
Signals (R ′, G ′, B ′ signals) obtained by inverting the polarities of the R, G, B signals are output from 2, 43 to the source drivers 47, 49, 51 of the LCD driver circuits 44, 45, 46. And R, G, B source drivers 47, 49, 5
1 displays the input video signal on the three liquid crystal panels 31, 32 and 33 for R, G and B.

FIGS. 4 to 6 are timing charts of signal waveforms of voltages applied to the three liquid crystal panels 31, 32 and 33 for R, G and B, and correspond to the timing charts of the signal waveforms of FIG. is doing.

As shown in FIGS. 4 to 6, the drive waveform of the voltage applied to the G liquid crystal panel 32 shown in FIG.
Further, the drive waveforms of the voltages applied to the R and B liquid crystal panels 31 and 33 shown in FIG.

When an image having a certain degree of correlation among R, G, and B colors is synthesized and displayed, a component for canceling out flicker due to an asymmetrical component of the voltage appears, and therefore, as in the liquid crystal projector shown in FIG. LCD panel 3
The color image formed by combining the images by 1, 32 and 33 by the optical system can reduce the occurrence of flicker as compared with the conventional case in which all three colors are inverted in phase.

As described above, the video signal processing unit of the liquid crystal projector of this embodiment generates the polarity inversion control signal based on the odd field and the even field discriminated by the synchronization processing circuit 14, and the polarity inversion control is performed. The signal is directly output to the polarity inverting circuits 41 and 43, and
A controller 15 that outputs an inversion signal of the polarity inversion control signal to the polarity inversion circuit 42 via an inverter 40;
Liquid crystal panel 31, G liquid crystal panel 32 and B liquid crystal panel 3
Of the three liquid crystal panels of No. 3, the polarity inversion signal supplied to the source driver of the G liquid crystal panel 32 is in phase with the polarity inversion signal supplied to the source drivers of the other two R and B liquid crystal panels 31, 33. Polarity inversion circuit 41 for inverting the polarities of the R, G and B signals so that
3 liquid crystal panels 3 for R, G and B equipped with 42 and 43
Since the phase of the AC waveform drive signal for driving the liquid crystal panel of at least one color among 1, 32, and 33 is shifted, flicker occurs due to the asymmetric component of the voltage when the images of the three liquid crystal panels are combined. The elements can be offset to alleviate the flicker phenomenon.

In this embodiment, the polarity inversion signal supplied to the source driver of the G liquid crystal panel 32 has a phase of 180 ° with respect to the polarity inversion signal supplied to the source drivers of the R and B liquid crystal panels 31 and 33. Although they are shifted, it goes without saying that any phase change may be made as long as the phase of the AC waveform drive signals of the three liquid crystal panels for R, G and B is shifted by at least one color. For example, the object whose phase is to be shifted may be another signal instead of the G signal, and the phase to be shifted may be an arbitrary phase change instead of the opposite polarity shifted by 180 °. In this case, only one color has the phase 1
Similar effects can be obtained by driving the three colors in different phases instead of shifting them by 80 °.

For example, when the phase difference between the polarity reversal control signals of R, G, and B is not 180 °, for example, when it is 60 °, as shown in FIG. 7, in this case, the polarity reversal circuits 41, 42 ,.
Before entering 43, the G and B signals are delayed by the time corresponding to the phase difference (the other control signals are similarly delayed). When the phase difference is not 180 °, it is conceivable that the color shift occurs due to the time difference.

Further, in this embodiment, the common electrode potential VCOM is
However, it is needless to say that the same can be applied to the case of common inversion drive in which VCOM is shaken in order to reduce the breakdown voltage.

In this embodiment, the liquid crystal display device is provided with the TFT3.
Although it is applied to a plate-type color liquid crystal projector, it is not limited to this, and the type, number, arrangement, etc. of liquid crystal panels are arbitrary, and other specific detailed structures and the like can be appropriately changed. Of course.

Further, it goes without saying that the circuits and matrixes constituting the video signal processing section, the number of gates, their types, etc. are not limited to those in the above-mentioned embodiments.

[0067]

According to the first, second, third, fourth, fifth and sixth aspects of the present invention, the phase of the AC drive waveform of at least one liquid crystal panel among the plurality of liquid crystal panels is shifted. It is possible to reduce the flicker phenomenon when the images of the liquid crystal panels are combined.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system of a liquid crystal projector of a first embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a circuit diagram of a video signal processing unit of the liquid crystal projector of the embodiment.

FIG. 3 is a waveform diagram of a primary color signal and a polarity inversion control signal of the liquid crystal projector of the same embodiment.

FIG. 4 is a timing chart of signal waveforms of voltages applied to the R liquid crystal panel of the liquid crystal display device of the example.

FIG. 5 is a timing chart of signal waveforms of voltages applied to the G liquid crystal panel of the liquid crystal display device of the example.

FIG. 6 is a timing chart of a signal waveform of a voltage applied to a B liquid crystal panel of the liquid crystal display device of the example.

FIG. 7 is a waveform diagram when the phase difference of the R, G, and B polarity inversion control signals of the liquid crystal projector of the embodiment is 60 °.

FIG. 8 is a circuit diagram of a video signal processing unit of a conventional liquid crystal projector.

FIG. 9 is a timing chart of signal waveforms of voltages applied to a liquid crystal panel of a liquid crystal display device.

[Explanation of symbols]

 11 Y / C separation circuit 12 Color demodulation circuit 14 Synchronization processing circuit 15 Controller 21 Metal halide lamp 22 Reflector 23, 24, 25 Reflecting mirror 26, 27, 28, 29 Dichroic mirror 31, 32, 33 Liquid crystal panel 34, 35, 36 Condenser Lens 37 Projection lens 40 Inverter 41, 42, 43 Polarity inversion circuit 44, 45, 46 LCD driver circuit 47, 49, 51 Source driver 48, 50, 52 Gate driver

Claims (6)

[Claims] 1. A plurality of liquid crystal panels and a liquid crystal display device for AC driving the plurality of liquid crystal panels to display an image in combination, wherein the phase of an AC drive waveform of at least one liquid crystal panel among the plurality of liquid crystal panels is A liquid crystal display device characterized by being shifted. 2. A plurality of liquid crystal panels and a liquid crystal display device for driving a plurality of the liquid crystal panels by an alternating current to synthesize and display an image, wherein at least one liquid crystal panel among the plurality of liquid crystal panels has a phase of an AC drive waveform. A liquid crystal display device characterized by having opposite phases. 3. A plurality of liquid crystal panels and a liquid crystal display device for AC driving the plurality of liquid crystal panels for composite display of images, wherein a phase of a voltage for AC driving the plurality of liquid crystal panels is changed for each liquid crystal panel. A liquid crystal display device characterized in that they are offset from each other. 4. The liquid crystal display device according to claim 1, wherein the plurality of liquid crystal panels are three liquid crystal panels for R, G, and B. . 5. The plurality of liquid crystal panels are three liquid crystal panels for R, G, B, and a phase of an AC drive waveform of a liquid crystal panel for G among the three liquid crystal panels for R, G, B. 3. The liquid crystal display device according to claim 2, wherein the liquid crystal display device has an opposite phase. 6. The liquid crystal display device is a liquid crystal projector that combines images generated on three liquid crystal panels for R, G, and B by reflection and transmission and enlarges and projects them on a screen. The liquid crystal display device according to claim 1, 2, or 3.