The hottest application cs7123 realizes vgaxga TV

Using cs7123 to realize vga/xga TV box design

cs7123 chip is a high-speed/high-precision video DAC chip designed independently by Shenzhen Xinhai Technology Co., Ltd. the tear strength value is generally related to sample shape, tensile speed and experimental temperature. It includes a three-way 10 bit current steering DAC, with a maximum sampling speed of 240mhz. The structure block diagram of cs7123 is shown in Figure 1. It includes three-way high-speed, 10 bit input video DA converter, standard TTL input and complementary output high impedance analog output current source. It has three independent 10 bit input ports, which can work under 5V single power supply or 3.3V single power supply

figure 1:cs7123 structure block diagram

cs7123 also has two additional video control signals, sync synchronization signal and blank black level control signal. Cs7123 also has a standby mode. Cs7123 is manufactured by 5V CMOS process, and the monolithic CMOS structure ensures low power performance. The main function of cs7123 is to convert three RGB signals into analog RGB signals and output them to the display screen for display. In addition, it can also be used as a three-way separate DAC

cs7123 is compatible with a variety of high-precision display systems, including rs-343a and RS-170, and can be widely used in HDTV and digital video systems (1600 × 1200@100Hz ）High resolution color pictures, digital RF modulation, image processing, medical B-ultrasound equipment, video signal reproduction, etc

the TV function of the computer is one of the mainstream consumer functions in the personal computer entertainment market. At present, there are three kinds of hardware used to receive TV programs through the computer or computer monitor. Among them, the most popular TV boxes are VGA (for CRT display) and XGA (for CRT and LCD display). They are easy to install and have clear TV signals. They can be used by simply connecting with the computer monitor. Their usage is basically the same as that of TV. Figure 2 shows the basic schematic diagram of a vga/xga TV box

figure 2:basic schematic diagram of vga/xga TV box

in Figure 2, the signal from the tuner is decoded to the video processing chip. The video processing chip outputs three channels of RGB digital signals to the video DAC, and then outputs three channels of analog RGB signals to the display screen for display. Among them, the speed of the video DAC directly determines the resolution of the output image, and special attention should be paid to its new characteristics when applying the granulator, while its accuracy determines the quality of the output image. The relationship between DAC speed and resolution can be obtained by the following formula: clock frequency = point rate = (horizontal resolution) × (vertical resolution) × (refresh rate)/(flyback coefficient); Horizontal resolution = number of pixels in the row; Vertical resolution = number of pixels in a frame

refresh rate is the required speed for screen refresh. The typical value is 60Hz for progressive scanning system and 30Hz for interlaced scanning; The flyback coefficient must consider that a specific part of the total time of each frame is blank. Generally, it can complete the mechanical property test of various data under the conditions of tension, contraction, zigzag, shear, etc. the horizontal tensile testing machine of steel wire rope adopts computer-controlled full experimental process. The typical value is 0.8, for example

therefore, if there is a 1024 × 1024@60Hz The backscatter factor is 0.8. Then: clock frequency = point rate =1024 × one thousand and twenty-four × 60/0.8=76.8Hz。 The clock frequency of the required DAC is 78.6mhz. The maximum clock frequency of cs7123 is 240mhz, so it can support up to 1600 × 1200@100Hz Resolution of

Figure 3 shows the typical circuit connection diagram of cs7123

when designing PCB, it should be noted that cs7123 should be as close to the connector as possible, so as to reduce the peak noise and reflection caused by impedance mismatch. In addition, a layer of ground plane should be laid on the signal line to improve the high-frequency power supply voltage rejection ratio

in order to obtain the best performance, each analog output needs to add a source matching resistor. The resistance value is related to the application environment. When the load is a double 75 Ohm load, the resistance value of the source matching resistance is also 75 ohm. Also note that this resistor should be as close to the chip as possible to reduce reflection

summary of this article

at present, the application of digital video is developing towards the direction of large screen and high definition, and the TV box is also developing in this direction. At present, the general VGA TV box supports 800 × 600@75Hz And the XGA TV box supports 1024 × 768@75Hz Resolution of. Cs7123 has high precision and speed, and can support up to 1600 × 1200@100Hz The market rate of Cuitingyuan food in Hefei administrative district is high, which is suitable for high-definition vga/xga TV box. (end)