The electromagnetism radiate of EMC study
[introduction] the radiate that what EMI pays close attention to is electromagnetism energy, include the interference of exterior electromagnetism environment to oneself system, and the interference of energy of oneself radiant electromagnetism to outside system. These interference cannot exceed a limit, exceeded this limit to be able to pose a problem, these disturb in the final analysis or the signal integrality that affected a system.
What EMI pays close attention to is the radiate of electromagnetism energy, include the interference of exterior electromagnetism environment to oneself system, and the interference of energy of oneself radiant electromagnetism to outside system. These interference cannot exceed a limit, exceeded this limit to be able to pose a problem, these disturb in the final analysis or the signal integrality that affected a system.
We are in when contacting strange thing, the knowledge that normally the habit is familiar with with oneself goes explaining him unfamiliar thing. EMC knowledge more involving go to microwave and radio frequency, to resembling me this is planted dedicated for the at signal integrality very little dish bird that knows to EMC knowledge, also can lever the gate that EMC designs at first only with a few ABC of SI. In my acknowledge, what EMI pays close attention to is the radiate of electromagnetism energy, include the interference of exterior electromagnetism environment to oneself system, and the interference of energy of oneself radiant electromagnetism to outside system. These interference cannot exceed a limit, exceeded this limit to be able to pose a problem, these disturb in the final analysis or the signal integrality that affected a system.
How does radiation go out the electromagnetism energy on circuit board?
Here, I remembered below this graph, this also is my basiccest to electromagnetism radiate impression.
Graph 1 The electromagnetism radiate of PCB
Inchoate PCB is lamina, it is to pass lead join to rise between chip, power supply cord and line do not have what distinction, it is connecting lead merely just. This let me think of this graduation is designed again, it is a sheet piece machine pilot LED displays screen, this system is very simple, with respect to a few IC and lubricious annulus resistor, capacitance does not have a few, through soldering simply, circuit can work. Did not use microstrip line at all, banding line, double skeining thread, coaxial cable these east.
After study high speed is designed, I understood, as the rise of frequency, signal jumps change the electromagnetism capabilities of generation also is adding. Between chip again also cannot so simple join rose, like the graph this kind 1 joins method, can make loop inductance very big, loop inductance is very big, can make the inductance that communicates signal very big, signal is met far from conscientiously edge lead travels, meet however radiation goes in the space.
How to solve the electromagnetism radiate problem of circuit board?
In SI engineer eye, use microstrip line is banding perhaps the line is to offer the transmission way of a low impedance to signal. This also is the need of electromagnetism screen in EMC engineer eye. Using microstrip line banding perhaps after the line, electromagnetism energy is controlled was in in the medium between conductor.
Why using microstrip line and banding after the line, is branch of electromagnetism energy greater part manacled to be in medium? Main reason is signal method and circumfluence method those who lean is closer, the inductance of so whole return was reduced. Do not believe us to use software to be calculated
What circumfluence method leans is close
What circumfluence method leans is far
By go up the graph is knowable, referenced plane is effective to the unit length of transmission line the influence of inductance is very big. Can imagine, below high frequency condition, if signal has very good circumfluence way, so the loop inductance that it experiences is met very small, signal can transmit sink from emissive end according to the apiration of people, the loop inductance that if signal feels,gets can produce radiation problem greatly very much.
Brief summary
In low frequency when, need not consider the issue that electromagnetism disturbs, the electromagnetism field change all round the lead when low frequency is done not have so intense, what the inductance effect of lead also won’t behave is so apparent. But arrived high frequency, electromagnetism field change is acuteness, method of should mature signal and the coupling problem that return way, use signal method and the inductance that return the coupling of method to reduce whole return, control the electromagnetism energy that lead launchs to the space.