JPH0435048B2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention uses at least three matrix-driven liquid crystal panels to display additive primary colors (red, green, and blue).
This invention relates to a small and lightweight projection device that controls each of the colored lights and adds and mixes them in an arbitrary ratio.

<Background of the Invention> Matrix liquid crystal panels, which are used as display panels for efficiently displaying large amounts of information, have a large number of pixel electrodes arranged in at least a dot matrix, and pixels that respond to voltages applied to them. It generally includes a liquid crystal layer that modulates light as a component, and displays any monochromatic image including halftones by applying a corresponding video signal to each picture element.

The operating mode of the LCD panel is twisted
Nemateytsuk (TN), Guest Host (GH),
There are many modes such as dynamic scattering mode (DSM), birefringence (such as DAP or ECB), and phase transition, all of which are applicable to the present invention. Conventional LCD television (TV)
In the application example, a monochrome image is displayed using a single panel. Driven by a Si wafer substrate with integrated MOS-FETs
Side clock-type LCD TVs using GH LCD panels and TN
Pocketable TVs using LCD panels have been commercialized. Details about liquid crystals can be found in Sasaki, ed., ``Fundamentals and Applications of Liquid Crystal Electronics,'' Ohmsha (1979).

Generally, one of the following three methods is used to individually control each picture element of a liquid crystal panel.

(1) Simple matrix method Striped row and column electrodes are provided on each of two substrates, and the panels are assembled by bonding them orthogonally to each other. A row selection signal is sequentially applied to the row electrodes, and an image signal is applied to the column electrodes in synchronization with the row selection signal. The intersection of the row and column electrodes becomes a picture element, and the liquid crystal sandwiched between the two electrodes changes its optical characteristics in response to the potential difference.

Since the liquid crystal is an element that responds to an effective value, driving using the voltage averaging method causes a problem of crosstalk, and the number of scanning lines cannot be set very large.

In order to overcome these problems, the following two methods have been developed.

(2) Addition of nonlinear elements Varistor, MIM (Metal/
Insulator/Metal) and other nonlinear elements are added,
This method suppresses crosstalk.

(3) Addition of switching elements This method adds a switching transistor to each picture element and drives it individually. A drive voltage is applied during the selection period, charging the storage capacitor and retaining it during the non-selection period. Note that the liquid crystal itself is a capacitive load, and if its time constant is sufficiently larger than the driving repetition period, the storage capacitor can be omitted.

As the switching transistor, a thin film transistor (TFT) or a MOS-FET formed on a silicon wafer is used.

The present invention provides particularly effective results in the above (2) and (3).

Conventional color LCD panels (for example,
-18886), coloring means for the three primary colors are arranged in a stripe or mosaic pattern on the same panel, and the additive colors are mixed using the same principle as a color cathode ray tube (CRT), so the additive primary colors (red, green, blue) are used. It will be done. It is not a good idea to use subtractive primary colors (yellow, cyan, magenta) in a system that performs such additive mixing because the color reproduction range becomes narrow.

In the present invention, an arbitrary color image is reproduced by using three liquid crystal panels as light valves that independently control the color light of the three primary colors.
The intensity of light in each of the red, green, and blue wavelength ranges is modulated by the corresponding liquid crystal panel, and as a result of combining them, any color is reproduced.

The selection criteria for the wavelength range of colored light used in the present invention are shown below.

Based on the concept of the brightest color, the present inventor has determined that the optimal conditions for effectively utilizing a white light source in additive color mixing and satisfying compatibility with NTSC TV signals are as follows. We found that the conditions are

[Red: Absorbs below 590nm, transmits above 590nm Green: Transmits between 495 and 565nm, below 495nm and
Absorbs 565nm or more Blue: Transmits 510nm or less and 665nm or more, 510~
665 nm] However, when using a dichroic mirror, which is one of the features of the present invention, to divide the light from a single white light source into three parts depending on the wavelength, this result cannot be used as is. However, some modifications are required. In other words, it is necessary that the spectra of the three colored lights do not overlap, and that when added together the three colors cover the entire visible range.

Considering the above matters, the wavelength range of each color light may be selected as follows.

[Red: longer wavelength than approximately 580nm Green: approximately 500 to 580nm Blue: shorter wavelength than 500nm] Conventional projection TVs use dedicated CRTs for each of the three primary colors, and the images reproduced by these are transmitted through a lens. This method projects images onto a screen. With current technology, CRTs are not bright enough, so they cannot be projected onto large screens. Also, since a directional screen is used to make the screen appear as bright as possible, the viewing angle becomes extremely narrow.

Furthermore, since it uses three large CRTs and is configured to be integrated with a screen, it is a very large device, and there are restrictions on where it can be installed.

Laser writing has already been proposed as a projection type liquid crystal display, but
Since it is a monochromatic display, it is fundamentally different from the present invention, and the apparatus is large-scale.

<Object of the Invention> In view of the above circumstances, an object of the present invention is to provide a new and useful projection device that is small, lightweight, bright, and independent of viewing angle by using at least three liquid crystal panels.

<Example> First, an active matrix substrate on which TFTs are integrated is manufactured. FIG. 1A is a schematic plan view of an example of a TFT, and FIG. 1B is a cross-sectional view thereof. The TFT is constructed by sequentially patterning and stacking a gate electrode 11, a gate insulating film 12, a semiconductor film 13, a source electrode 14, and a drain electrode 15 on a transparent insulating substrate 10 made of glass or the like. The drain electrode 15 has a picture element electrode 1
6 and an optional storage capacitor 17 are connected. Thin film formation methods include vacuum evaporation, sputtering, CVD, and plasma CVD.
method, low-pressure CVD method, etc. are used, and patterning is performed using shadow mask and photoringraphy techniques. In order to drive the liquid crystal on the substrate on which this TFT is formed, a light shield and an alignment film are further provided. When an n-type semiconductor is used as the semiconductor film 13, when a positive voltage is applied to the gate electrode 11, an electron accumulation layer is formed at the interface of the semiconductor film 13 on the gate insulating film 12 side, and the source electrode 14 and the drain electrode 1
5 is reduced. FIG. 1C is a wiring diagram when driving a liquid crystal with a TFT panel. A scanning pulse is periodically applied to the gate electrode 11,
The TFT is turned on (ON). In synchronization with this, an image signal is applied to the source electrode 14,
The voltage is applied to the picture element electrode 16 and a storage capacitor 17 provided as necessary through the TFT to drive the liquid crystal. The storage capacitor 17 is used to maintain the voltage to be applied to the liquid crystal even while the TFT is in the OFF state. If the time constant of the liquid crystal is sufficiently larger than the scanning period, there is no need to provide a storage capacitor. Next, a substrate on the counter electrode side is prepared, in which a transparent conductive film and an alignment film for aligning liquid crystal are provided on a transparent substrate such as glass.

These two substrates are bonded together via a spacer, and liquid crystal is injected into the gap between the two substrates. Three such liquid crystal panels are manufactured for each color of red, green, and blue. If the liquid crystal mode is TN, polarizers are provided on both sides of each panel. Note that each panel only needs to be able to control red, green, and blue color light, and each panel itself does not necessarily need to be provided with coloring means for the respective colors.

This liquid crystal panel is driven as follows.
An example of a block diagram of the drive circuit is shown in FIG.
The TV radio waves are processed by a series of TV receiving circuits 30 ranging from a tuner to a color demodulation circuit to become red, green, and blue color video signals. The video signal of each color is applied to the liquid crystal panels 21 to 23 corresponding to each color with polarity depending on the display mode of the liquid crystal. The video signals R (red), G (green), and B (blue) of each color are input to analog line memories 31 to 33 consisting of shift registers and sample hold circuits, and video signals for one line are stored. Next, this one line worth of video signal is output to the source line 14 in synchronization with the scanning signal generated by the scanning pulse generation circuit 34. Scanning pulses are sequentially applied to gate line 11, and the FETs on that line are
Turn it on. In this way, the video signal is sampled and sampled at the appropriate timing to each picture element electrode.
It is held and the LCD is controlled. This liquid crystal panel is incorporated into an optical system consisting of a light source 40, a condenser lens 41, a projection lens 42, dichroic mirrors 43, 44, and a mirror 45, as shown in FIG. 3, to construct a projection TV. Incandescent lamps, halogen lamps, xenon lamps, etc. are used as light sources, but the spectrum of the light source does not necessarily have to be a continuous spectrum;
It may be a fluorescent tube or a discharge tube that emits a green and blue bright line spectrum. In this case, it is desirable that the center wavelengths of the bright line spectra be around 610 nm, 540 nm, and 460 nm, respectively, from the viewpoint of color reproduction range and compatibility with NTSC signals. The dichroic mirrors 43 and 44 are for dividing the light from the light source into three wavelength bands of red, green, and blue, modulating each color light with a liquid crystal panel, and then combining it again. A dichroic mirror is a stack of multiple thin films with different refractive indexes, and uses interference effects to reflect only light in a specific wavelength range and transmit the rest. 43 selectively reflects red light and transmits other light. 44 selectively reflects blue light and transmits other light. According to such a configuration, light of each wavelength from a single light source can be used effectively, and the light utilization efficiency is higher than that of a method in which only light in a necessary wavelength range is transmitted through an absorption filter.

Although the resolution of the reproduced image is determined by the number of picture elements of each panel, it cannot be increased indefinitely due to the manufacturing technology, yield, cost, etc. of the liquid crystal panel. If the number of picture elements is small, the reproduced image will have poor image quality. If the number of pixels in a horizontal line is smaller than the horizontal resolution of an NTSC TV signal (approximately 350 lines), the spatial resolution of human vision is high for brightness and low for hue. , an apparently smooth image can be obtained by doing the following.

The three liquid crystal panels are set so that the images of each picture element are not exactly superimposed on each other, but are shifted from each other by about 1/3 of the picture element pitch in two directions as shown in FIG. 4B. If the picture elements of each color are overlapped accurately without shifting as shown in Figure 4A, shadows of gates, lines, sources, and lines will appear between the picture elements in a grid pattern, and the reproduced image will be rough, but the picture elements of each color If you shift them by 1/3, they will fill in the grid-like shadows mentioned above, resulting in a smooth image. In the diagram, R, G, B
are red, green, and blue picture elements, respectively. At this time, the change in hue produces a high spatial frequency component, but this is not perceptible to the human eye due to visual characteristics. still,
Naturally, it is better to sample the video signal to be applied to the picture elements of each color at a timing that corresponds to the shifted position of each picture element.

When the light from the light source is strong, in order to prevent the liquid crystal panel from heating up and changing its operating characteristics, air cooling is performed using a fan or liquid cooling is performed by immersing the liquid crystal panel in insulating oil as necessary.

A project constructed in this way
TVs have become as compact as slide projectors, and have more flexibility in installation location than traditional projection TVs, allowing for example the ability to project onto the ceiling or hang from the ceiling and project onto a wall. become. Furthermore, it is also possible to freely change the screen size by changing the projection distance or replacing the projection lens.

In addition, if the projection plane is not perpendicular to the optical axis of the optical system,
This may cause problems such as the rectangular screen deforming into a trapezoid or being out of focus, but it is possible to "tilt" the optical system (change the angle between the liquid crystal panel and the optical axis of the optical system) as shown in Figure 5. This can be solved by introducing it.

<Effects of the Invention> As described above, the present invention constitutes a liquid crystal projection device that is small, lightweight, bright, and independent of viewing angle, and has great practical value.

It should be noted that the scope of application of the present invention is not limited to TVs, but it is obvious that it can also be applied to character displays and graphic displays as displays for various information processing devices.

[Brief explanation of drawings]

FIGS. 1A, B, and C are a schematic plan view, a schematic cross-sectional view, and a wiring diagram of the TFT. FIG. 2 is a block diagram of a liquid crystal projection television apparatus showing one embodiment of the present invention. FIG. 3 is a block diagram of the optical system of the liquid crystal projection television apparatus shown in FIG. 2. FIGS. 4A and 4B are explanatory diagrams illustrating the arrangement of picture elements. FIG. 5 is an explanatory diagram of the "tilt mechanism" in the liquid crystal projection television device. 11... Gate electrode, 12... Gate insulating film,
13... Semiconductor film, 14... Source electrode, 15...
...Drain electrode, 16...Picture element electrode, 17...Storage capacitor, 21, 22, 23...Liquid crystal panel, 30...TV signal receiving circuit, 31, 32, 3
3... Analog line memory, 34... Scanning pulse generation circuit, 40... Light source, 41... Condenser lens, 42... Projection lens, 43, 44
...Dichroitsk mirror, 45...Mirror.

Claims (1)

[Scope of Claims] 1. A liquid crystal projection system in which at least three liquid crystal panels are arranged that are driven by an active matrix and each independently controls projection light of three additive primary colors to project and display a display pattern in which additive colors are mixed. The device is provided with a dichroic mirror that splits the light emitted from a single light source and projects it onto different optical paths, and the liquid crystal panel is arranged on each optical path of the projection light that is projected via the dichroic mirror. . A liquid crystal projection device, wherein the projection lights of the three primary colors that have passed through each of the liquid crystal panels are aligned on the same optical axis by an optical path bending means and then projected and displayed. 2 The wavelength range of the colored light controlled by each panel is [Red: longer wavelength side than λ ₁ Green: λ ₁ ~ λ ₂ Blue: shorter wavelength side than λ ₂ However, λ ₁ = 560 ~ 600 nm, λ ₂ = 480 ~ 520nm, which represents the wavelength at which the intensity of the color light that each liquid crystal panel should control is 50% of its peak. ] The liquid crystal projection device according to claim 1, which is selected so as to satisfy the following.