Projector classification and LCD, DLP, LCoS projection comparison

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Projectors can be divided into front projection systems (referred to as front projection) and rear projection systems (referred to as rear projection) according to the relative positions of users, projectors and screens.

The so-called front projection means that the projector is placed on the same side of the screen as the user. At this time, the image projected by the projector onto the screen is reflected in the eyes of the audience.

Rear projection refers to the placement of the projector and the user on both sides of the screen. The light from the projector is projected onto the screen from the other side, and then penetrates the screen before being observed by the human eye.

HALFMOON Projector Classification

The projector optical system is generally composed of a light source, an illumination system, a display chip, and a projection lens. The light sources used mainly include bulbs-ultra-high pressure mercury lamps, Xenon lamps, solid light sources-light emitting diodes (LED), lasers (Laser) and so on. Display chips include LCD liquid crystal panels, DMD chips, and LCOS liquid crystal panels. Among them, LCD liquid crystal panels are transmissive systems, and DMD and LCOS are reflective systems.

Projector Classification

Under different chips, the structure of the lighting system is also different, so according to the choice of different display chips to determine the matching of the lighting system and the imaging system. The lighting system mainly needs to converge and homogenize the light emitted by the light source, so that the energy of the light source can be used to the maximum and irradiate the display chip evenly. The commonly used homogenization system is mainly divided into light tunnel (light tunnel). ) And flyeye lens.

In general, the projection lens is a device that magnifies the displayed image on the chip. It depends on the lighting system to decide whether to use a telecentric optical path or a non-telecentric optical path for matching. There are fixed-focus lenses and zoom lenses. The size of the lens is mostly related to factors such as the size of the display chip and the field of view.

Projectors are divided into CRT (Cathode Ray Tube) projection system, LCD (Liquid Crystal Display) projection system, LCOS (Liquid Crystal on Silicon) projection system and DLP (Digital Light Processor) projection system according to different display modes.

HALFMOON Projector Classification

CRT projector

It is usually called a three-gun projector. The CRT projector decomposes the input signal source into three beams of red, green, and blue light, and projects them on three CRT tube fluorescent screens full of phosphors. The phosphors emit light under high pressure.

The projected color image appears on the screen.

LCD projector

The LCD projection system projects the white light emitted by the light source onto the dichroic mirror to divide it into three beams of red (R), green (G), and blue (B), and then pass through the R, G, and B three-color liquid crystal panels respectively. The liquid crystal molecules with electro-optical effect change their arrangement under the action of an electric field, which affects the light transmittance of the liquid crystal molecules, which in turn changes the optical properties, and produces images with different grayscale gradients and different colors. The transmitted light is converged by a prism, and then enlarged and projected by an optical lens to form a pattern that is uniform in color with the source image.

LCOS projector

A new type of reflective projection display technology developed on the basis of LCD transmissive projection technology. The LCOS technology uses CMOS semiconductor technology to embed the active pixel matrix on the silicon wafer substrate that can be injected into the liquid crystal package by controlling the reflection of light, and directly realizes the driving circuit on the silicon wafer. The LCOS projector has high resolution and is integrated with the micro display device through the drive circuit part, thereby simplifying the circuit structure.

DLP projection

Among them, DLP® is a technology developed based on DMD (Digital Mirror Device) digital micro-reflective devices, invented by Dr. Larry Hornbeck of Texas Instruments (TI) in 1987. The DMD chip is a very complex photoelectric switch, which contains millions of micromirror matrices mounted on hinges. The size of each micromirror is a few microns. For example: DLP4710 has 1920×1080 micro lens arrays, pixels up to 2 million, and the size of the micro lens is 5.4 microns. Under the control of the driving signal, the "switch" can be in the "fully open" state (inclined to the light source), or in the "fully off" state (deviation from the light source), or in between. It is possible to control the ratio of the number of opening and closing times of the micromirror per unit time to achieve the required grayscale requirements of the projection screen. When the number of opening times of the DMD micromirror exceeds the number of closing times, the pattern is a light gray pixel; When the number of opening times is less than the number of closing times, it is a dark gray pixel. The switching times of each micromirror can reach thousands of times per second. The gray scale of the DLP projection system is 0~1024, which can get very detailed projection graphics or video signals.

Projector Classification

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