JPH04207678A - Liquid crystal projection type television - Google Patents

Abstract

PURPOSE:To obviate the generation of black floating or brightness grading even if this television is used as a top hanging type or floor type and to display images with good uniformity by varying the gain of video signals. CONSTITUTION:A drive IC control circuit 14 displays the images of a liquid crystal panel vertically and laterally reverse in the case of, for example, top hanging use and, therefore, the shift direction of the shift registers of a signal drive IC 17 and a scanning drive IC 19 and the input direction of a start pulse are changed. On the other hand, a vertical switch 13 controls an amplifier control circuit 1 as well to change the gain of the amplifier 11. Namely, the bottom end of the screen of the liquid crystal panel is eventually impressed with the effective voltage lower than a standard and the top end with a high effective voltage if vertical scanning is executed from the bottom end of the liquid crystal panel by impressing signals. Then, the angle theta1 between incident light and the liquid crystal molecules 43 at the top end of the liquid crystal panel and the angle theta2 with the liquid crystal molecules 43 at the bottom end of the liquid crystal panel are nearly theta1=theta2. The black float is improved in this way and the display uniform over the entire part of the screen is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a liquid crystal projection television that enlarges and projects images displayed on a liquid crystal panel onto a screen.

BACKGROUND OF THE INVENTION Liquid crystal panels are being actively researched and developed as a means of realizing flat-screen televisions because they can be constructed in a lightweight and thin screen.

However, there are many challenges, such as the difficulty of making the screen larger.

Therefore, liquid crystal projection televisions, which enlarge and project images displayed on a small liquid crystal panel onto a screen, are attracting attention. Characteristics of LCD projection TVs include: ■ A large screen can be obtained even with a small LCD panel; ■ The same resolution as a direct-view type TV can be obtained even with 1/3 the number of pixels; ■ The biggest disadvantage of a direct-view type LCD panel. There are no problems with viewing angles, and ■It is smaller and lighter than the cathode ray tube direct-view TV system. etc.

A conventional liquid crystal projection television will be described below. First, the liquid crystal panel used in the liquid crystal projection type television shown in FIG. 7 will be explained. As shown in FIG. 7, its components include a drive IC 19 (hereinafter referred to as a scanning drive IC) that applies signals to the gate signal lines G1 to Go of the liquid crystal panel, and a reference numeral 17 a source signal line 81 of the liquid crystal panel. A drive IC (hereinafter referred to as signal drive Ic) that applies a video signal to ~Sn, 71 is a thin film transistor (hereinafter referred to as TPT), 72 is an additional capacitor, and 73 is a display pixel having a liquid crystal layer. . The LCD panel is a scanning drive IC
19 applies a voltage that turns the TPT 71 on (hereinafter referred to as on voltage) or turns it off (hereinafter referred to as off voltage). The voltage to be written is output, and this voltage is sequentially held in each display pixel. This voltage changes the transmittance of the liquid crystal, modulating the light and displaying an image. Further, the scanning direction in which the on-voltage of the scan drive IC 19 is applied is normally G, , G2 . G8
....It is carried out in the direction of Go. FIG. 8 shows a terminal diagram of the external appearance of the scanning drive 1c19. In Figure 8, SPI/SF3 is the start pulse input terminal,
o is an output signal line connected to the gate signal line, R/L is a terminal for switching the shift direction inside the scan drive IC (
Hereinafter, it is a shift direction switching terminal). Further, CK is a clock input terminal, and the data in the shift register circuit in the scan drive IC 19 is shifted by 1 bit at the rising edge of the clock applied to the clock input terminal CK. Furthermore, when the data input to the start pulse input terminal SPI is shifted to the final stage of the shift register, it becomes a carry pulse and is output from the start pulse input terminal SP2. If the input logic of the shift direction switching terminal is opposite to the above, the data input to the start pulse input terminal SP2 becomes a carry pulse when shifted to the final stage of the shift register, and the data input to the start pulse input terminal SP2 becomes a carry pulse.
P! It is output from

Next, the drive circuit system of a conventional liquid crystal projection television will be explained using FIG. 6. As shown in Fig. 6, its components include an amplifier 11 for adjusting the gain of the video signal to a specified level, 15 a phase division circuit that generates positive and negative video signals, and 16 for each frame or field. 18 is a timing control circuit for controlling the timing of the signal drive IC 17 and the scan drive IC 19 to display an image on the liquid crystal panel 10. Regarding the related operations of these components, first, the gain of the video signal is adjusted by the amplifier 11 so that the video signal amplitude corresponds to the electro-optical properties of the liquid crystal baffle.

Next, the gain-adjusted video signal enters the phase division circuit 15, and this circuit produces two video signals of positive polarity and negative polarity. Next, the two video signals enter an output switching circuit 16, which outputs a video signal whose polarity is inverted for each field. The reason for inverting the polarity of the signal for each frame is to prevent deterioration of the liquid crystal by applying an alternating current voltage to the liquid crystal. Next, the video signal from the output switching circuit 16 is transferred to the signal drive IC1.
7, and the signal drive IC 17 outputs a signal to the source signal line of the liquid crystal panel 10 in response to control signals such as a horizontal start pulse and a clock from the timing control circuit 18. On the other hand, the scan drive IC 19 also applies an on-voltage to the gate signal line and scans in synchronization with the signal drive 1cI7 using control signals such as a vertical start pulse and a scan clock from the timing control circuit 18. An image is displayed on the liquid crystal panel 10 as described above. Next, the state of liquid crystal molecules when the liquid crystal panel is driven will be explained. FIG. 9 is an explanatory diagram of the state of liquid crystal molecules and the direction of light incidence on the liquid crystal panel. In the ninth [D(a), 41 is a field lens arranged on the light incident side of the liquid crystal baffle, 42a and 42b are glass substrates, and 43 is a liquid crystal molecule. Further, FIG. 9(b) is a graph showing the screen brightness when the display on the liquid crystal panel is projected onto the screen. For ease of explanation, it is assumed that the liquid crystal panel is in a normally white mode, and when a voltage with a large absolute value is applied, liquid crystal molecules stand up and display is performed. On the other hand, when the voltage applied to the liquid crystal is low, the liquid crystal molecules lie down, resulting in a white display. Further, it is assumed that the same image is displayed on the entire screen of the liquid crystal panel (hereinafter referred to as solid image display). Furthermore, in the case of a display, a state in which the amount of charge held in the liquid crystal is small, that is, a state in which the effective voltage is low, is called a state in which the amount of charge held in the liquid crystal is small, that is, a state in which the effective voltage is low. The case of village display will be explained below.

Figure 9 (al indicates the state of the liquid crystal molecules in the case of village display. The upper edge of Figure 9 (a) is the upper edge of the screen, and the lower edge is the lower edge of the screen. Note that the inclination of the liquid crystal molecules 43 is easy to explain. The above is exaggerated in order to make it more accurate.The above is the same in the following drawings.As shown in Section 911(a), in order to display a rough image, when scanning sequentially from the top to the bottom of the screen of the liquid crystal panel, , the effective voltage applied to the liquid crystal at the bottom edge of the screen is lower than at the top edge of the screen.

This is caused by the parasitic capacitance between each pixel and the signal line, the parasitic capacitance of the TPT 71, etc. Therefore, the liquid crystal molecules at the top of the liquid crystal panel screen have a larger rising angle than the liquid crystal molecules at the bottom. When parallel light is incident on the liquid crystal panel in this state, the angle of incidence between the light and the liquid crystal molecules at the bottom of the screen increases, so the black at the bottom of the screen appears floating. Therefore, a field lens 41 is arranged on the incident side of the liquid crystal panel, and as shown in FIG. 9(a), the direction of incidence of light on the top edge of the screen of the liquid crystal panel is directed downward, and the direction of incidence of light on the bottom edge is directed upward. do. Then, the incident angle θ1 between the liquid crystal molecules 43 at the upper end of the liquid crystal panel and the light and the incident angle θ2 between the liquid crystal molecules 43 at the lower end of the liquid crystal panel and the light become approximately equal. Therefore, as shown in FIG. 9(b), the display is uniform from the top end to the bottom end of the liquid crystal panel. Note that the function of the field lens is not only to correct the brightness gradient described above, but also to condense light.

Problems to be Solved by the Invention Among liquid crystal projection televisions, there is a front type that projects an enlarged image onto a reflective screen. The front type is mainly used by standing on the floor or desk as shown in FIG. 10(b). However, due to issues such as space for installation, the first
As shown in Figure 0 (b), so-called ceiling hanging applications, in which devices are attached to ceilings, are also being expanded. Therefore, there is a growing need for a front-type LCD projection television that can be used both for stationary use and for ceiling-mounted use. However, the stationary type shown in Fig. 10 (0)) is
If you try to use it as a ceiling-mounted type as shown in Figure 1, it will be installed in an upright position and an inverted position, making it necessary to reverse the displayed image on the liquid crystal panel vertically and horizontally. Horizontal reversal can be easily handled by simply changing the scanning direction of the not register of the liquid crystal panel's signal drive Ic and the input of the start pulse, but vertical reversal causes the problems explained below due to the effective voltage applied to the liquid crystal. do. FIG. 11 shows the state of liquid crystal molecules when scanning is performed from the bottom to the top of the screen of the liquid crystal panel. In other words, the display is displayed upside down. As described above, when scanning from the bottom edge of the liquid crystal toward the top edge, the slope θ2 between the light and the liquid crystal molecules at the bottom edge of the screen becomes smaller than the slope θ1 between the light and the liquid crystal molecules at the top edge of the screen.

In other words, the relationship is θ2 x θ1. Therefore the 11th
As shown in Figure (bl), the black at the top edge of the screen is raised and the bottom edge of the screen is depressed, resulting in non-uniformity in black display. Standing,
The present invention aims to provide a liquid crystal projection type television that automatically performs display in both inverted and inverted positions.

Means for Solving the Problems In order to solve the above problems, the liquid crystal projection television of the first aspect of the present invention includes a switching circuit for switching the vertical scanning direction of the liquid crystal panel, and a switching circuit for changing the gain of the video signal in conjunction with this switching circuit. It is equipped with a circuit that makes the effective voltage applied to the upper end of the liquid crystal panel higher than the standard value and lower the effective voltage applied to the lower end of the liquid crystal panel. Furthermore, the LCD projection television of the second aspect of the invention converts the video signal for one field into A/D and stores the data in the field memory, and when the LCD projection television is used as a stationary type, this is done on a first-in, first-out basis. Read from field memory and perform D/A conversion. When a liquid crystal projection television is used as a ceiling-mounted type, the data in the field memory is read out on a first-in, last-out basis and subjected to D/A conversion.

Effect: In the liquid crystal projection television of the present invention having the above configuration, brightness gradient or black floating occurs when the vertical scanning line is scanned upside down using a switching circuit. However, by lowering the effective voltage applied to the liquid crystal at the upper end of the liquid crystal panel and lowering the effective voltage applied to the liquid crystal at the lower end, the problem of masculinity is improved. Further, in the liquid crystal projection television of the second aspect of the present invention, the vertical scanning direction is not changed from the upper end to the lower end, and the video signal is
/D conversion is performed, the image is temporarily stored in a memory, and then read out in reverse order and displayed sequentially from the upper end of the liquid crystal panel to the lower part of the display image, so that floating black does not occur.

Embodiment Hereinafter, an embodiment of the liquid crystal projection television according to the first aspect of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram of a liquid crystal projection television according to an embodiment of the first invention. Note that the arrangement of field lenses and the like is the same as in FIG. 9. As shown in FIG. 1, the component 12 is an amplifier control circuit, and this amplifier control circuit 12 is a so-called gain control means that controls the amplification factor of the amplifier 11 in real time. Reference numeral 14 denotes a drive IC control circuit, which has the function of controlling the shift direction switching terminal R/L and start pulse input terminal SPI/SF3 of the scan drive IC 19, and the function of controlling the shift direction and start pulse input of the signal drive IC 17. Reference numeral 13 denotes an up/down detection means, and more specifically, a configuration as shown in FIG. 2 can be considered.

In FIG. 2, 21 is a cylindrical container, and 23 is mercury poured into the container 21. Also, 22a, 22
b and 22c are terminals. This vertical detection means 13 (
Hereinafter, this will be referred to as the up/down switch. ) is fixed in a liquid crystal projection type television, and when used as a stationary device, a mercury 23 is used to shoot between terminals 22b and 22c. In addition, when using it as a ceiling mount, the container 21 is inverted and the mercury 2
3 shoots between terminals 22a and 22b. Therefore, between terminals 22a and 22b (designated A in FIG. 2) and terminal 2
By monitoring the resistance value between 2b and 22c (indicated by B in the second article), it is possible to automatically detect whether the LCD projection television is being used as a stationary or ceiling-mounted television.

It goes without saying that a manual switch may be provided instead of using the up/down switch 13 as shown in FIG. 2. The operation of a liquid crystal projection television set according to an embodiment of the above-mentioned components of the first aspect of the present invention will be described below. When the up/down switch 13 determines whether the device is to be used as a stationary device or a ceiling mount device, the drive Ic control circuit 14 is controlled. For example, when using a ceiling mount, the drive IC control circuit 14 changes the soft direction of the soft registers of the signal drive 1c17 and the scan drive IC 19 and the input direction of the start pulse in order to display the displayed image on the liquid crystal panel upside down and horizontally. let On the other hand, the up/down switch 13 also controls the amplifier control circuit 12, and the amplifier 11
change the gain of The output waveform of the amplifier 11 is shown in FIG. The signal waveform shown in FIG. 3 is a video signal waveform for an evening screen. 3r'', 31 is a signal waveform in which the gain of the amplifier 11 is not controlled by the amplifier control circuit (hereinafter referred to as a pre-correction signal waveform), and 32 is a signal waveform in which the gain of the amplifier 11 is not controlled by the amplifier control circuit 12. This is the signal waveform in the corrected state (hereinafter referred to as the corrected signal waveform).If you apply the signal as shown in Figure 3 and perform vertical scanning from the bottom edge of the liquid crystal panel, the bottom edge of the screen of the liquid crystal panel will be the reference point. The effective voltage is lower than that of the upper end, and a higher effective voltage is applied to the upper end.The state at that time is shown in FIG. The angle θ1 between the angle θ1 and the angle θ2 between the liquid crystal molecules 43 at the lower end of the liquid crystal panel becomes approximately θ1−θ2.Therefore, as shown in FIG. 4(b), the floating is improved and becomes uniform over the entire screen. Portions such as the phase splitting circuit 15 are the same as those of the prior art, so a description thereof will be omitted.

Hereinafter, an embodiment of the liquid crystal projection type television according to the second invention will be described with reference to the drawings. FIG. 5 is a block diagram of a liquid crystal projection television according to an embodiment of the second invention. 51a in the 5th area.

51b is a field memory, which can store image data of two screens, A and B. The signals from the amplifier 11 are A/D converted and sequentially stored in the field memories 51a and 51b. When one screen of data is stored in the field memory A31a, the field memory 851
The data for the next screen is stored in b. Furthermore, the data of the next screen is overwritten in the field memory A31a. The screen data is alternately stored and held in the field memories A-B in the following manner. Further, data in the field memory where screen data is not being written, that is, the field memory A 31a or the field memory 851b, is sequentially read out, D/A converted, and transferred to the next phase division circuit 15. Reference numeral 52 denotes a memory control circuit which switches the data being read from the field memory between first-in, first-out and first-in, last-out. In other words, the stored screen data is switched between reading the stored screen data starting from the data at the top of the screen (first in, first out) and reading out the stored screen data starting from the data at the bottom of the screen (first in, last out). Reference numeral 53 denotes an up/down detection means, and specifically, the up/down switch shown in FIG. 2 or a manual switch is often used. Also, this up/down switch is the drive IC control circuit 1.
4, this drive IC control circuit 14 controls the shift register of the signal drive IC 17 and the input direction of the start pulse, as described in the description of the first embodiment of the present invention, and performs horizontally inverted display. have them do it. The operation of the liquid crystal projection television set according to the second embodiment of the present invention having the above configuration will be described below. First, the video signal is subjected to gain adjustment by the amplifier B, A/converted, and alternately input to the field memories A31a-851b. The reading of data from the field memories 51a and 51b differs depending on whether the liquid crystal projection television is used in a ceiling-mounted manner or in a stationary manner by means of an up-and-down switch to prevent the image on the screen from being reversed during projection.

When a ceiling mount is used, the memory control circuit 52 reads data from the field memory in a first-in, last-out manner. At this time, at the same time, the drive IC control circuit 14 controls the signal drive IC to cause the image display to be displayed horizontally and inverted. Conversely, when the device is used as a stationary device, the memory control circuit 52 reads data from the field memory in a first-in, first-out manner, and at the same time, the drive IC control circuit 14 controls the signal drive IC to make the image display normal. The screen data read out from the field memory is D/A converted and sent to the phase division circuit 15.
is input. The other operations are the same as those of the conventional system or the first embodiment of the present invention, so the description thereof will be omitted. As described above, in the liquid crystal projection type television set according to the embodiment of the second invention, the vertical scanning direction scans from the top end of the screen to the bottom end, both when the TV is mounted on a ceiling and when it is placed on a table.

When using a ceiling mount, the data in the field memory is read out first in, last out, and an image is displayed upside down. Therefore, the tilt of the liquid crystal molecules is as shown in Figure 9 (a
), there is no black floating like in the conventional case, and the display is uniform across the entire screen.

In addition, in this specification, explanation has been given using an example of improving black floating in a liquid crystal projection type TV using a normally white liquid crystal panel, but the invention is not limited to this, and It goes without saying that in projection televisions, it is possible to improve the white level, that is, the brightness slope of white.

Furthermore, in this specification, the LCD projection television is expressed as a front-type television, but it is not limited to this; it may also be a rear-type LCD projection television that displays images on a transmissive screen. Needless to say.

Effects of the Invention As is clear from the above explanation, in the LCD projection television of the first invention, the mounting method is changed, and when the state is changed from upright mounting to inverted mounting, or vice versa. ,
By varying the gain of the video signal when performing up-and-down vertical scanning, and by changing the way the field memory is read out, the liquid crystal projection television of the second aspect of the invention can be installed even when used as a ceiling-mounted type. Even when used as a stationary type, there is no occurrence of black floating or brightness gradient, and extremely uniform image display can be performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a liquid crystal projection television according to an embodiment of the first invention, FIG. 2 is a block diagram of a vertical direction detection means used in the embodiment, and FIG. 3 is a video signal waveform of the embodiment. Figure, 4th
Figure (a) is a schematic diagram showing the configuration of the liquid crystal panel of the same example,
Fig. 4 To) is a graph showing the brightness distribution of the liquid crystal panel of the same embodiment, Fig. 5 is a block diagram of the liquid crystal projection type television according to the second embodiment of the present invention, and Fig. 6 is the conventional liquid crystal projection type. A block diagram of a television; Fig. 7 is a configuration diagram of an active matrix/multilayer array; Fig. 8 is a circuit diagram showing the terminal arrangement of a scanning drive Ic; Fig. 9(a) shows a conventional liquid crystal panel configuration in use. The side view, Figure 11 (a) is a schematic diagram showing the configuration of the liquid crystal panel when a conventional liquid crystal panel is used in an inverted state, and Figure 11 (g)) shows the brightness distribution of the same liquid crystal panel. This is a graph showing. 10...Liquid crystal panel, 11...Amplifier, 12...Amplifier control circuit, 13...
Up/down detection means, 14... Drive IC control circuit, 15... Phase division circuit, 16... Output switching circuit, 17... Signal drive IC,
1B... Timing control circuit, 19...
・Scanning drive IC. Name of agent: Patent attorney Haruaki Ogata Two people Figure 1/θ-'X product panel 15-Phase splitting circuit yt---
Amplifier 16---L circuit 1
2---Asian type 7th vb / 7---Suzuhara Dry Life I6 Fig. 5/ Fig. 6 Fig. 10 Fig. 11 Fig. 47 仝zo ttz
p on the screen 1 1' l! t1 side bottom f

Claims (4)

[Claims] (1) a liquid crystal panel that modulates incident light with a video signal; a scanning device that drives and scans the liquid crystal panel with the video signal; a switching device that switches the vertical scanning direction of the scanning device; and gain control means for varying the gain of the video signal according to the vertical scanning direction, and the gain control means controls the modulation level of the liquid crystal panel every time the switching means switches the vertical scanning direction. An LCD projection television that changes. (2) The liquid crystal projection television set according to claim 1, further comprising up/down detection means for detecting an upright mounting state and an inverted mounting state, and the switching means is driven by the up/down detection means. (3) A liquid crystal panel that modulates incident light according to a video signal, a field memory that stores the video signal field by field, and a field memory control means that switches the reading direction of the field memory, and controls the field memory. A liquid crystal projection type television set in which the image display state of the screen displayed on the liquid crystal panel is displayed in a normal display state or in a vertically inverted display state where the image display state is reversed. (4) The liquid crystal projection television set according to claim 3, further comprising up-and-down detection means for detecting an upright mounting state and an inverted mounting state, and said field memory control means is driven by said up-down detection means.