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CX25870 参数 Datasheet PDF下载

CX25870图片预览
型号: CX25870
PDF下载: 下载PDF文件 查看货源
内容描述: 视频编码器与自适应闪烁过滤和HDTV输出 [Video Encoder with Adaptive Flicker Filtering and HDTV Output]
分类和应用: 电视编码器
文件页数/大小: 291 页 / 3791 K
品牌: CONEXANT [ CONEXANT SYSTEMS, INC ]
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3.0 PC Board Considerations  
CX25870/871  
3.5 Signal Interconnect  
Flicker-Free Video Encoder with Ultrascale Technology  
3.5 Signal Interconnect  
3.5.1 Digital Signal Interconnect  
The digital inputs to the CX25870/871 should be isolated as much as possible  
from the analog outputs and other analog circuitry. Also, these input signals  
should not overlay the analog power plane or analog output signals.  
Most of the noise on the analog outputs will be caused by fast transitioning  
clock edges, data edges (less than 3 ns), and overshoot, undershoot, and ringing  
on the digital inputs.  
The digital edge rates should not be faster than necessary because feedthrough  
noise is proportional to the digital edge rates. Lower-speed applications will  
benefit from using lower-speed logic (3–5 ns edge rates) to reduce data-related  
noise on the analog outputs.  
Transmission lines will mismatch if the lines do not match the source and  
destination impedance. This will degrade signal fidelity if the line length  
reflection time is greater than one-fourth the signal edge time. Line termination or  
line-length reduction is the solution. For example, logic edge rates of 2 ns require  
line lengths of less than 4 inches without use of termination. Ringing can be  
reduced by damping the line with a series resistor (30–50 ).  
Radiation of digital signals can also be picked up by the analog circuitry. This  
is prevented by reducing the digital edge rates (rise/fall time), minimizing ringing  
with damping resistors, and minimizing coupling through PC board capacitance  
by routing the digital signals at a 90-degree angle to any analog signals.  
The clock driver and all other digital devices must be adequately decoupled to  
prevent noise generated by the digital devices from coupling into the analog  
circuitry.  
3.5.2 Analog Signal Interconnect  
The CX25870/871 analog output traces should be located as close as possible to  
the output connectors and be of equal length to minimize noise pickup and  
reflections caused by impedance mismatch.  
The analog outputs are susceptible to crosstalk from digital lines; therefore  
digital traces must not be routed under or adjacent to the analog output traces.  
To maximize the high-frequency power supply rejection, the video output  
signals should overlay the ground plane.  
For maximum performance, the analog video output impedance, cable  
impedance, and load impedance should be the same. The load resistor connection  
between the video outputs and GND should be as close as possible to the  
CX25870/871 to minimize reflections. Unused DAC analog outputs should be left  
floating.  
3-10  
Conexant  
100381B