Double Layer PCB board - design and routing principles
The two-layer board ground wire is designed as a grid-shaped frame, that is, the parallel lines are printed on the side of the printed circuit board, the other side is the vertical ground of the copy board, and then connected with the metal via holes Hole resistance to be small).
In order to take into account each IC chip should be installed near the ground, often every 1 ~ 115cm cloth a ground, so dense ground to make the signal loop area smaller, Double Layer PCB is conducive to reducing radiation. The ground network design method should be in the cloth signal line before, otherwise it is more difficult to achieve.
Two - layer pcb board signal line wiring principle
Double board in the rational layout of the components to determine, followed by the first design to copy the power cord, and then cloth important line --- sensitive lines, high-frequency lines, cloth after the general line --- low-frequency line. The key lead is preferably a separate power supply, ground circuit, Double Layer PCB lead and very short, so sometimes in the key line edge of a ground line close to the signal line, let it form the smallest working loop.
Four-layer board top, the bottom of the wiring principle with the two-layer signal line, but also the first cloth key crystal, crystal circuit, clock circuit, CPU and other signal lines, must follow the circulation area as small as possible principle.
PCB IC circuit work, the front mentioned many times in front of the circulation area, the actual source of its difference in the concept of differential mode radiation. Such as differential mode radiation definition: the circuit current flowing in the signal loop, the signal loop will produce electromagnetic radiation, Double Layer PCB because this current is differential mode, so the signal loop radiation is called differential mode radiation, the radiation Field calculation formula: E1 = K1 · f2 · I · A / γ
In the formula: E1 --- differential mold copy board circuit space γ radiation field intensity from the differential mode radiation formula can be seen, the radiation field strength and the operating frequency f2, circulation area A, operating current is proportional to, such as when When the operating frequency f is determined, the size of the circulation area is the key factor that can be directly controlled in our design. At the same time, the working speed and current of the circulation are as long as the reliability is better. The bigger the better, the narrower the jump The larger the wave component, the wider, the higher the electromagnetic radiation, Double Layer PCB the greater the power of its current must be large (the above has been pointed out), which we do not expect. The faster the circuit switch, the smaller the area allowed.
The key to the line, if possible around it can be surrounded by the ground. After the PCB copy board is finished, the available ground will cover all the voids, but it must be noted that these covered ground lines should be shorted with the low impedance of the large strata, Double Layer PCB which can achieve good results (Note: Should meet the conditions, such as creepage distance, etc.).