KR20040046137A - Projection system with reflective type liquid crystal display device - Google Patents

Abstract

PURPOSE: A projection system having a reflective LCD(Liquid Crystal Display), LCOS(Liquid Crystal On Silicon) is provided to perform a rapid response speed and possess optical conditions for realizing a high contrast ratio, thereby capable of implementing an effective moving picture and a high image quality. CONSTITUTION: A light source(2) emits a white light. A color converter(4) converts the white light emitted from the light source(2) into RGB lights sequentially. A polarized beam splitter(6) splits the RGB lights transmitted the color converter(4) into an S-polarized light and a P-polarized light. An LCOS(8) receives the S-polarized light from the polarized beam splitter(6) and then drives the liquid crystal by a unit of pixel. A projection lens system(12) projects the image implemented by the LCOS(8) to a screen(10). A polarized plate(14) is attached to a surface of the polarized beam splitter(6) received the RGB lights or the front surface of the LCOS(8).

Description

Projection system with reflective liquid crystal display {PROJECTION SYSTEM WITH REFLECTIVE TYPE LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a projection system having a reflective liquid crystal display, and more particularly, to a one-panel projection system for time-divisionally driving one reflective liquid crystal display to implement a color screen.

So-called liquid crystal on silicon (LCOS) is known as the reflective liquid crystal display. The Elcos is a liquid crystal cell formed on a semiconductor substrate, and since the components and switching circuits of each pixel are highly integrated, an elliptical size of about 1 inch can be realized in a high resolution screen of over XGA level.

Therefore, in a projection system in which a large screen image is provided by enlarging and projecting a screen of a display device, efforts are being made to apply Elcos as a display device of a projection system for miniaturization and high resolution of a projection system.

The projection system using the Elcos is a three-panel method and a 1-panel method. The three-panel method is to provide R, G, B light to each of the three Elcos, and to synthesize a single color image implemented in each Elcos into a color image, the one-panel method is one Elcos It provides a color image by sequentially providing the R, G, and B light, and time-division driving the Elcos.

The 1-panel projection system has fewer parts compared to the 3-panel method, and the optical configuration is simple, which is economical in manufacturing. However, the Elcose projection system has a sufficiently high response speed due to the time-sharing driving of the Elcos. Should be. In general, the response speed of Elcos required to effectively implement video is 1.5 ms or less. However, the well-known response rate of Elkos is approximately 4 to 8 ms, and the response speed does not meet the standard to be applied to the 1-panel projection system.

The response speed of the Elcos depends mainly on the cell gap of the Elcos. The elcos cell gap is the optical phase retardation of the Elcos with the birefringence of the liquid crystal (Δn, the difference between the major axis and the minor axis). , As an important factor for determining Δn × d), it is possible to realize a high contrast ratio when the factors such as the phase delay value of Elcos, the polarization axis of the polarizing plate, the twist angle of the liquid crystal and the like are optimally combined. Thus, a typical Elcos has a range of phase delay values that match the optical conditions for realizing high contrast ratios.

Accordingly, if the cell gap of the Elcos is set small in order to shorten the response speed of the Elcos, a liquid crystal material having a high birefringence should be used to satisfy the phase delay value in the above-described range. However, since the birefringence of the liquid crystal is proportional to the viscosity of the liquid crystal, an effort to improve the response speed by increasing the viscosity of the liquid crystal lowers the response speed of the Elcos, so that no substantial effect is obtained. Moreover, there are technical difficulties in setting the cell gap of Elcos below a certain range due to manufacturing process problems.

Therefore, in order to realize the above-described one-panel type projection system, it is necessary to have an elcos with a sufficiently fast response speed by adjusting the phase delay value, and to achieve a high contrast ratio corresponding to the elcos phase delay value. Optical conditions must be provided.

Accordingly, an object of the present invention is to solve the above problems, and an object of the present invention is to realize a high image quality by providing optical conditions for realizing a high contrast ratio, which is effective in realizing a video by increasing the response speed of a reflective liquid crystal display. To provide a one-panel projection system.

1 is a schematic diagram of a projection system according to an embodiment of the present invention.

FIG. 2 is a partially enlarged cross-sectional view of the reflective liquid crystal display shown in FIG.

3 is a schematic view for explaining a polarization axis of a polarizing plate.

4 and 5 respectively show the voltage according to the polarization angle change of the polarizing plate when the phase delay of the reflective liquid crystal display satisfies the condition of Equation 1 and the twist angle of the liquid crystal satisfies the condition of Equation 2 and Equation 3, respectively. -Graph showing the reflection curve.

In order to achieve the above object, the present invention,

A light source that emits white light, a color converter that receives white light and sequentially converts the light into R, G, and B light, a polarization beam splitter that receives R, G, and B light into S-polarized light and P-polarized light; And a polarizing plate that selectively transmits light vibrating in the same direction as its polarization axis among light vibrating at arbitrary wavelengths, and a vertically aligned liquid crystal layer, and receiving S-polarized light from the polarizing plate and the polarizing beam splitter. A reflective liquid crystal display that implements an image by driving a star, and a projection lens system that enlarges and projects an image implemented by the reflective liquid crystal display on a screen, wherein the reflective liquid crystal display and the polarizing plate are subject to the conditions (1) or (2) below. Provides a projection system that satisfies

(1) 0.1 ≦ Δn × d (μm) ≦ 0.13, α = -45 °, β = 0 °

(2) 0.1 ≦ Δn × d (μm) ≦ 0.13, α = -5 ° or 0 °, β = 90 °

Here, Δn × d represents the phase retardation of the reflective liquid crystal display, α represents the angle between the horizontal axis of the polarizing plate and the polarization axis, and β represents the twist angle of the liquid crystal constituting the liquid crystal layer.

Preferably, the reflective liquid crystal display satisfies the following condition (3).

(3) 0.07 ≦ Δn ≦ 0.08, 1 ≦ d (μm) ≦ 1.5

Here, Δn represents the birefringence of the liquid crystal, and d represents the cell gap of the reflective liquid crystal display.

In addition, the liquid crystal layer of the reflective liquid crystal display is made of a nematic liquid crystal having a birefringence in the range of 0.07 to 0.08.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram of a projection system according to an embodiment of the present invention.

The projection system includes a light source 2 emitting white light, a color converter 4 sequentially converting white light emitted from the light source 2 into R, G, and B light, R passing through the color converter 4, A polarization beam splitter 6 which separates G and B light into S-polarized light and P-polarized light, and a reflective liquid crystal display which receives S-polarized light from the polarization beam splitter 6 and drives the liquid crystal pixel by pixel. 8) (hereinafter referred to as 'Elcos' for convenience), and a projection lens system 12 which enlarges and projects the image implemented by the Elcos 8 onto the screen 10, and provides R, G, and B light. The polarizing plate 14 is attached to one surface of the receiving polarizing beam splitter 6 or the front of the elcos 8.

The light source 2 is provided with an elliptical reflector plate 16 so that the white light emitted from the light source 2 is irradiated to the color converter 4, and the color converter 4 is a known color switch or color wheel. Can be used, and converts white light into R, G, B light sequentially and provides it to the polarizing beam splitter 6.

Preferably, a pair of fly-eye lenses 18 and a polarization conversion system (PCS) 20 may be located between the color converter 4 and the polarization beam splitter 6. The fly-eye lens 18 improves the uniformity of light reaching the elcos 8 by its lens arrangement, and the polarization conversion system 20 provides unstable polarization emitted from the light source 2. It serves to convert the light of the state into a light of a stable polarization state advantageous for driving the Elcos (8).

As such, the polarizing plate 14 provided with light through the polarization conversion system 20 selectively transmits the light oscillating in the same direction as its polarization axis, and the polarizing beam splitter 6 transmits the light passing through the polarizing plate 14. Is separated into S-polarized light and P-polarized light, and among them, S-polarized light having good reflection efficiency is provided to Elcos (8). The Elcos 8 receives S-polarized light to drive a liquid crystal for each pixel to implement a screen, and the image reflected by the polarization beam splitter 6 includes a projection lens system in which optical lenses (not shown) are combined. 12) is enlarged and projected onto the screen (10).

FIG. 2 is a partially enlarged cross-sectional view of the elcos shown in FIG. 1, and the elcos 8 includes a semiconductor lower substrate 24 having a semiconductor integrated circuit 22 as a switching element therein, and a liquid crystal layer 26. An upper substrate 28 integrally combined with the semiconductor lower substrate 24 therebetween, and a transparent electrode 30 functioning as a common electrode is formed on one surface of the upper substrate 28 facing the liquid crystal layer 26. On one surface of the lower semiconductor substrate 24 facing the liquid crystal layer 26, reflective electrodes 32 functioning as pixel electrodes are formed.

The reflective electrode 32 and the semiconductor integrated circuit 22 are provided for each pixel and electrically connected to each other. Accordingly, when the semiconductor integrated circuit 22 applies a driving signal to the reflective electrode 32 of the pixel, the reflective electrode 32 applies an electric field to the liquid crystal layer 26 together with the transparent electrode 30 to transmit light per pixel. By changing the to realize a predetermined image.

As described above, the elcos 8 receives the R, G, and B light sequentially to implement color images by time division driving. In the present embodiment, the liquid crystal layer 26 of the elcos 8 is in a voltage-free state. In addition to having a vertical alignment structure in which the liquid crystal molecules are placed upright, the elcos 8 is set so that a phase retardation (Δn × d) value indicating an optical phase delay effect satisfies the following condition.

0.1 ≤ Δn × d (μm) ≤ 0.13

As can be seen from the above equation, the phase retardation of the elcos 8 depends on the birefringence of the liquid crystal (Δn, the difference between the major and minor axial refractive indices) and the cell gap d of the elcos 8. In the example, the birefringence of the liquid crystal for realizing the above-described phase delay condition is preferably in the range of 0.07 to 0.08, and the cell gap d of the elcos 8 is preferably in the range of 1 to 1.5 mu m.

More specifically, the elcos 8 configures the liquid crystal layer 26 using nematic liquid crystals having the above-described birefringence characteristics, and the liquid crystal molecules 26 are erected in a state where no voltage is applied. It has a vertically oriented structure that is located. In addition, the elcos 8 is set to a normal-black state that blocks light in the off state to increase the contrast ratio of the screen.

In addition to the phase delay characteristic of the elcos 8 described above, the projection system according to the present embodiment corresponds to the optical conditions for realizing an optimum contrast ratio in response to the phase delay characteristic of the elcos 8 (e.g., Polarization angle of the polarizing plate and the twist angle of the liquid crystal) are provided as follows.

In the projection system according to the present embodiment, as the first embodiment, when the Elcos 8 satisfies the above-described phase delay condition, the polarization angle of the polarizing plate 14 (α, the angle between the horizontal axis of the polarizing plate and the polarizing axis, see FIG. 3). And twist angle β of the liquid crystal satisfy the following modification condition.

α = -45 °, β = 0 °

Also, in the projection system according to the present embodiment, when the elcos 8 satisfies the above-described phase delay condition, the polarization angle α of the polarizing plate 14 and the twist angle β of the liquid crystal are expressed by the following equation. Make sure the conditions are met.

α = -5 ° or 0 °, β = 90 °

Table 1 below shows the response speed change of the liquid crystal according to the phase retardation of the Elcos (8). Both the Comparative Examples and Examples were experiments with the Elcos with the nematic liquid crystal having a birefringence in the range of 0.07 to 0.08 Proceeded.

Phase delay (Δn × d) (μm) Response speed (ms) Comparative Example 1 0.25 8 to 10 Comparative Example 2 0.2 6 to 8 Example 1 0.13 1 to 1.5 Example 2 0.1 1 to 1.5

As such, when the phase delay of the Elcos 8 satisfies the conditions of the embodiment, it can be confirmed that the response speed is reduced compared to the Elcos of the Comparative Example. Therefore, the elcos 8 according to the present embodiment smoothly time-division driving as the response speed is shortened, and the function can be smoothly performed even in the video implementation.

4 is a graph showing a voltage-reflection curve according to a change in polarization angle α of a polarizer when the phase delay of Elcos satisfies the condition of Equation 1 and the twist angle β of the liquid crystal is 0 °. The polarization angles of the polarizing plates applied to Examples and Comparative Examples 1 to 3 are shown in Table 2 below. In the graph, the greater the change in reflectance according to the voltage change, the higher the contrast ratio.

Polarization angle (α) of polarizer Example -45 ° Comparative Example 1 -30 ° or -60 ° Comparative Example 2 -15 ° or -75 ° Comparative Example 3 0 ° or -90 °

As described above, the projection system according to the present embodiment realizes a high contrast ratio by changing the reflectance from 0 to 1 as the voltage increases, whereas the projection systems of Comparative Examples 1 to 3 do not exceed the maximum 0.8 as the voltage increases. It can be seen that the contrast ratio is low. In particular, in Comparative Example 3, since there is no change in reflectance according to voltage change, the display itself becomes impossible.

FIG. 5 is a graph showing a voltage-reflection curve according to a change in polarization angle α of a polarizer when the phase delay of Elcos satisfies the condition of Equation 1 and the twist angle β of the liquid crystal is 90 °. The polarization angles of the polarizing plates applied to Examples and Comparative Examples 1 to 5 are shown in Table 3 below.

Polarization axis of polarizing plate (α) Example 1 0 ° or -5 ° Comparative Example 1 -15 ° Comparative Example 2 -30 ° Comparative Example 3 -45 ° Comparative Example 4 -60 ° Comparative Example 5 -75 °

As shown in FIG. 5, in the case of Examples 1 and 2, the reflectance is changed from 0 to 1 according to the increase of the voltage to implement a high contrast ratio, whereas in the case of Comparative Examples 1 to 5, the reflectance is increased according to the voltage increase. The maximum contrast could not be exceeded 0.81, indicating a low contrast ratio. In particular, in the case of Comparative Example 5, since there is no change in reflectance according to the voltage change, the display itself becomes impossible.

As described above, the projection system according to the present embodiment shortens the response speed of the Elcos 8 to implement a video, provides a high-quality screen with high contrast ratio, and uses the aforementioned Elcos 8 to 1-. It can drive effectively by a panel system.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the range of.

As described above, according to the present invention, the response speed of the reflective liquid crystal display can be shortened to realize a video, and a high contrast ratio can be provided to provide a high quality screen. Therefore, the projection system according to the present invention can be effectively driven in a one-panel manner using the reflective liquid crystal display.

Claims (7)

A light source emitting white light; A color converter for sequentially converting white light emitted from the light source into R, G, and B lights; A polarizing beam splitter for separating the R, G, and B light emitted from the color converter into S-polarized light and P-polarized light; A polarizing plate which is combined with the polarizing beam splitter and selectively transmits light vibrating in the same direction as its polarization axis among light vibrating at an arbitrary wavelength; A reflective liquid crystal display including a liquid crystal layer having a vertical alignment structure and receiving S-polarized light from the polarizing plate and the polarizing beam splitter to implement an image by pixel-by-pixel driving of the liquid crystal layer; And It includes a projection lens system for magnifying and projecting the image implemented by the reflective liquid crystal display on the screen, A projection system in which the reflective liquid crystal display and the polarizer satisfy the following conditions. 0.1 ≦ Δn × d (μm) ≤ 0.13, α = -45 °, β = 0 ° Here, Δn × d represents the phase retardation of the reflective liquid crystal display, α represents the angle between the horizontal axis of the polarizing plate and the polarization axis, and β represents the twist angle of the liquid crystal constituting the liquid crystal layer. A light source emitting white light; A color converter for sequentially converting white light emitted from the light source into R, G, and B lights; A polarizing beam splitter for separating the R, G, and B light emitted from the color converter into S-polarized light and P-polarized light; A polarizing plate which is combined with the polarizing beam splitter and selectively transmits light vibrating in the same direction as its polarization axis among light vibrating at an arbitrary wavelength; A reflective liquid crystal display including a liquid crystal layer having a vertical alignment structure and receiving S-polarized light from the polarizing plate and the polarizing beam splitter to implement an image by pixel-by-pixel driving of the liquid crystal layer; And It includes a projection lens system for magnifying and projecting the image implemented by the reflective liquid crystal display on the screen, A projection system in which the reflective liquid crystal display and the polarizer satisfy the following conditions. 0.1 ≤ Δn × d (μm) ≤ 0.13, α = -5 ° or 0 °, β = 90 ° Here, Δn × d represents the phase retardation of the reflective liquid crystal display, α represents the angle between the horizontal axis of the polarizing plate and the polarization axis, and β represents the twist angle of the liquid crystal constituting the liquid crystal layer. The method according to claim 1 or 2, And the polarizer is located on one side of the polarizing beam splitter opposite the color converter or on the front of the reflective liquid crystal display. The method according to claim 1 or 2, The reflective liquid crystal display, A semiconductor lower substrate having a semiconductor integrated circuit as a switching element therein; Reflective electrodes connected to the semiconductor integrated circuit and provided for each pixel; An upper substrate coupled to the semiconductor lower substrate through the liquid crystal layer; And And a transparent electrode formed on one surface of the upper substrate facing the liquid crystal layer. The method according to claim 1 or 2, A projection system in which the reflective liquid crystal display satisfies the following conditions. 0.07 ≤ Δn ≤ 0.08, 1≤ d (μm) ≤ 1.5 Here, Δn represents the birefringence of the liquid crystal, and d represents the cell gap of the reflective liquid crystal display. The method according to claim 1 or 2, And a liquid crystal layer of said reflective liquid crystal display comprising a nematic liquid crystal having a birefringence in the range of 0.07 to 0.08. The method according to claim 1 or 2, And a pair of fly-eye lenses and a polarization conversion system between the color converter and the polarization beam splitter.