LCD Monitor

Introduction

The monitor is the computer screen (Computer Screen / Display). The monitor receives the signal from the computer and forms an image, acting like a television receiver. Some computer screens use liquid crystal displays. Computer screens are also called visual displays.

constitute

Let's take a look at the composition of the liquid crystal display. Generally speaking, a liquid crystal display consists of the following parts:

1. LCD module

Glass substrate: Liquid crystals and grid-like printed circuits are inside. Timing control: used to generate the timing and voltage required to control the deflection of liquid crystal molecules. Lamp tube: produces a white light source. Backlight: Reflect the light generated by the lamp tube onto the LCD screen.

2. Control board

The control board plays the role of signal conversion. Convert signals of various input formats into signals of fixed output format. For example, the input signal for a 1024 x 768 screen can be 640 x 480, 800 x 600, 1024 x 768, etc., and finally converted into an output format of 1024 x 768, 1920 x 1080, 3840 x 2160.

3. Inverter

Generate high voltage to light the tube.

Make up the circuit:

Video amplifier circuit: It can be divided into two parts: pre-video amplifier and video amplifier output. The pre-viewer receives the display card from the signal interface. Amplify the R, G, and B three primary color video signals to drive the video amplifier output stage. The output stage of the video amplifier is the power amplifier: large stage, amplify the video signal sent from the pre-view amplifier stage to sufficient power, drive the cathode of the kinescope, and modulate the intensity of the electron beam emitted by the cathode. After the electron beam bombards the phosphor screen, the electricity is completed. A light conversion function can display images in conjunction with scanning.

Usually this part of the circuit also has functions such as contrast control, line and field blanking, and white balance adjustment.

Field scanning circuit: including field oscillation and field output. The field oscillating circuit forms a vertical frequency sawtooth wave under the synchronization signal, and the sawtooth wave is amplified by the power of the field output circuit and then added to the vertical deflection coil to form a scanning current, so that the electrons emitted by the electron gun are pulled up and down.

The function of adjusting the field amplitude and field center is also realized in the field scanning circuit. In addition, the field frequency sawtooth wave is output to the pincushion correction circuit to correct the horizontal pincushion distortion.

Line scanning circuit: including several parts such as line oscillation, line output, high voltage circuit, pillow correction circuit and so on.

The line oscillating circuit outputs periodic rectangular pulses under the action of the line synchronization signal, and the rectangular pulse drives the line output circuit to generate a scanning current in the line deflection coil.

The high-voltage circuit transforms the high-amplitude retrace pulses generated during the reverse stroke of the horizontal scan, and then rectifies and filters them to obtain multiple voltage outputs. Among them, G1 is the kinescope grid voltage, SCREEN is the acceleration voltage, and FOCUS is the focus voltage. . H.V is the anode high voltage.

The realization of line center and line width adjustment functions are also included in the line scan circuit.

Switching power supply: Most displays use pulse width modulation switching power supply, which is composed of a switching tube (adjustment tube), a converter, a sampling circuit, a comparison amplifier circuit, a reference power supply, an exciter and a protection circuit. The circuit of the switching power supply is simple and easy to maintain.

Pattern recognition and control circuit: The function of this circuit is to determine which display mode is currently being based on the characteristics of the line and field synchronization signals sent by the display card, and control the line scan and field scan circuits accordingly to eliminate mode conversion The impact on the working state of the circuit, such as changing the free oscillation frequency of the line oscillation and field oscillation circuit, adjusting the line amplitude and field amplitude, and changing the operating voltage of the line output stage.

technical parameter:

Resolution

Resolution refers to the sum of pixels that make up an image, that is, how many pixels the screen contains. It is generally expressed as the product of the horizontal resolution (the number of pixels in a scan line) and the vertical resolution (the number of scan lines). For example, 1920×1080, it means that the horizontal direction contains 1920 pixels and the vertical direction is 1080 pixels. The total number of pixels on the screen is their product. The higher the resolution, the more pixels the picture contains, and the more delicate and clear the image. The resolution of the display is affected by the size of the display, (picture tube dot pitch), circuit characteristics, etc.

Grating pitch and dot pitch

The grating pitch refers to the distance between the parallel gratings of a cathode-grid picture tube (in mm). The advantage of using a cathode-grid picture tube is that its grating pitch will not be deformed after being used for a long time, and the display will not suffer from deterioration in picture quality after many years of use.

Dot pitch (or stripe pitch) is a very important hardware indicator of the display. It refers to the distance between a light-emitting point of a given color and the nearest neighboring light-emitting point of the same color. This distance cannot be changed by software. This is different from the resolution. At any same resolution, the smaller the dot pitch, the clearer and more delicate the displayed image, and the higher the resolution and image quality.

Bandwidth is a very important parameter of the display, which can determine the performance of the display. The so-called bandwidth is the abbreviation for the width of the passband of the display video amplifier. The bandwidth of a circuit actually reflects the circuit's response speed to the input signal and the resolution capability of the display. The wider the bandwidth, the smaller the inertia, the faster the response speed, the higher the signal frequency that is allowed to pass, and the smaller the signal distortion. The unit of bandwidth is MHz, and its value can be calculated using the formula "horizontal resolution × vertical resolution × refresh rate".

Refresh rate

The refresh rate of the display is divided into vertical refresh rate and horizontal refresh rate. The vertical refresh frequency is also called the field frequency, which refers to the number of times the display repeatedly refreshes the display screen per second, expressed in Hz. This refresh rate is commonly referred to as refresh rate; horizontal refresh rate is also called horizontal frequency (Horizontai scanning trequency), which refers to the number of times the display scans horizontal lines per second, in kHz; vertical refresh rate vertical frequency (Vertical scanning trequency) The unit of frequency is MHz, which is determined by the horizontal refresh rate and the screen resolution. The vertical refresh rate indicates how many times the screen image is redrawn per second, that is, the number of screen refreshes per second.

Common types

From the early black and white world to the color world, displays have gone through a long and arduous journey. With the continuous development of display technology, the classification of displays has become more and more detailed. There are more than 500 LED display factories in Shenzhen. Among them, 40% mainly provide processing services, as well as small workshop-style production, and there are also a group of production enterprises focusing on quality and research and development .

CRT monitor

A CRT monitor is a monitor that uses a cathode ray tube (Cathode Ray Tube). It is mainly composed of five parts: electron gun, deflection coil, shadow mask, phosphor layer and glass shell. Although CRT flat-panel displays have the advantages of large viewing angles, no dead pixels, high color reproduction, uniform chroma, multi-resolution modes that can be adjusted, and extremely short response time, LCD displays have the advantages that they are difficult to surpass, but they have been withdrawn from the market. .

LCD display

The LCD display is the liquid crystal display. Its advantages are thin body, small footprint and small radiation.

There are a lot of liquid crystal particles inside the LCD display, they are regularly arranged into a certain shape, and their colors on each side are different, divided into red, green and blue. These three primary colors can be reduced to any other colors. When the display receives the display data, it will control each liquid crystal particle to rotate to a different color surface, thereby combining different colors and images. Because of this, the shortcomings of LCD monitors include insufficient color and low viewing angle.

LED display

LED display is a display screen that displays text, graphics, images, and animation by controlling the display mode of semiconductor light-emitting diodes.

The technological progress of LED is the biggest driving force to expand market demand and application. Initially, LEDs were only used as micro-indicators and were used in high-end equipment such as computers, audio and video recorders. With the continuous advancement of large-scale integrated circuits and computer technology, LED displays have risen rapidly.

LED display integrates microelectronics technology, computer technology, and information processing technology. With its bright colors, wide dynamic range, high brightness, long life, stable and reliable work, it has become the most advantageous new generation of display equipment. At present, LED displays have been widely used in large squares, stadiums, stock exchange halls and other places to meet the needs of different environments.