Is it necessary to use series termination resistors on the output pixel port pins? I see they are not used in the ADV7619_7511 evaluation board but only on the LLC pin. Are they necessary to lower emissions?
It is not necessary to use series resistor however to reduce EMI and potential cross talk issue the series resistors help. Note EMI is caused by signal fast slew rates and overshoot ringing.
To reduce slew rate and ringing
1) series resistors reduce slew rate reducing overshoot
2) output drive strength controls can reduce slew rate reducing overshoot
3) trace length to reduce reflection issues
4) trace impedance control
LLC is a constant clock and will generally fundamental EMI generator.
Pixel port outputs can produce EMI under special conditions like displaying alternating vertical white and black one pixel wide lines.
The best bet is to play it safe, keep layout to short traces on 50 Ohm boards with series resistors. The signals in order of priority should be be LLC, HS, VS, DE and pixel port.
Always check your layout with signal integrity tools for slew rate and ringing problems
I see what your saying about using the resistors to lower EMI. Concerning EMI is does using common mode chokes on the input HDMI lines help to reduce EMI?
You need to know what frequencies are violating CISPR and then track down their source in the system. If the violation is coming from radiated noise on the input cable then common mode chokes might help, or possibly one big choke around the entire cable. Normally common mode choke will be used on the transmitter, not the receivers.
Common mode chokes can help a bit with ESD protection however common ESD protection diode arrays do the job well enough.
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