As shown in the figure, the circuit that I saw during the internship is really unable to analyze the role of RC?
Nicklas Posted on November 30, 2020
π-type filter + 75Ω termination + AC coupling
Prudence Posted on November 30, 2020
This should be an analog video signal (CVBS), C163, L20, and C166 form a π-type filter circuit to filter out noise.
The characteristic impedance of the analog video signal transmission line is 75 ohms. If there is no terminal, it needs to be terminated externally (R278).
C168, pass AC signal, block DC.
Kiefer Posted on November 30, 2020
I thought so. Since I am matching, it should be for my entire CVBS receiving end, so the matching resistance should be hung at the forefront. Afterwards, a capacitor is used to block the direct current, then the signal at this time should have a relatively small amplitude, and the amplitude of the positive and negative ends is similar. Moreover, some low-frequency signals have been eliminated. After passing through the pi filter, other clutters will be directly filtered out and sent directly to the video processing IC. This ensures that the CVBS signal entering the video processing IC is good. And for small amplitude signals entering the filter, it feels more reliable.
