The main reason for this phenomenon is because the signal loop area is too large, not only produced a strong electromagnetic radiation, but also make the circuit sensitive to external interference. The easiest way to improve the electromagnetic compatibility of a line is to reduce the loop area of critical signals.
The key signal:
From the electromagnetic compatibility point of view, the key signal mainly refers to produce strong radiation signals and sensitive to the outside world. Signals that produce strong radiation are typically periodic signals, such as low-level signals of clocks or addresses. Signal that is sensitive to interference refers to those analog signals with low level.
Reduce the area of the circuit method:
A simple way is to lay a ground wire on the edge of the critical signal line, which should be as close as possible to the signal line. This results in a smaller loop area, reducing the sensitivity of differential mode radiation to outside interference. When a ground line is added next to a signal line, a loop of the smallest area is formed, and the signal current will certainly pass through this loop, not the other ground path.
If it is a double-sided circuit board, you can place a ground wire along the signal line on the other side of the circuit board, just under the signal line, and try to make the line as wide as possible. The loop area thus formed is equal to the thickness of the board multiplied by the length of the signal line.
In addition, the double-decker board should use the ground grid without exception to reduce the impedance of the ground. When using a ground grid, there is always a ground adjacent to the signal line, forming a smaller loop area. And in the wiring, should try to make the key line near the ground. Only for particularly critical lines (which produce very strong radiation or are particularly sensitive). Just need to set the ground line close to the signal line.