For experienced designers probably it is easy question but I am reading "Signal and Power integrity, E. Bogatin" and don't understand one thing.
"The two most common sources of EMI are the conversion of some differential signal into a common signal which eventually gets out on an external-twisted pair cable and ground circuit board generating common currents on external single-ended shielded cables."
My questions are
- why differential lines can be such big problems ? It is good in communication lines because it provides immunity to environment noise (like rs485) but why in opposite side it is bad for EMI ?
- ground common currents on shielded cable - this is about current in the shielding which emmits radiation ? If shielding is connected on both sides the problem doesn't exist ?
Sorry if that's stupid questions but it is my begining in signal integrity and EMI field.