Introduction
When doing PCB design, we often encounter various problems, such as impedance matching, EMI rules, etc.
Details
- How to consider impedance matching when designing high-speed PCB design schematics?
When designing high-speed PCB circuits, impedance matching is one of the design elements. The impedance value has an absolute relationship with the wiring method, which means that the impedance value can only be determined after wiring.Generally, simulation software cannot take into account some wiring conditions with discontinuous impedance due to the limitation of the circuit model or the mathematical algorithm used. At this time, only some terminators, such as series resistance, can be reserved on the schematic diagram to ease the wiring impedance. Discontinuous effect. The real solution to the problem is to try to avoid impedance discontinuities when wiring.
- When designing high-speed PCBs, which aspects should designers consider EMC and EMI rules?
Generally, EMI/EMC design needs to consider both radiation and conduction. The former belongs to the higher frequency part (<30MHz) and the latter is the lower frequency part (<30MHz). So you can't just pay attention to the high frequency and ignore the low frequency part.
A good EMI/EMC design must take into account the location of the device, PCB stack arrangement, important connection method, device selection, etc. at the beginning of the layout. If there is no better arrangement beforehand, it will be solved afterwards. It will get twice the result with half the effort and increase the cost.
In addition, pay attention to the return path of high-frequency signal current to make the loop area as small as possible (that is, loop impedance as small as possible) to reduce radiation. The ground can also be divided to control the range of high-frequency noise. Finally, properly choose the chassis ground between the PCB and the housing.
- When making PCB boards, in order to reduce interference, should the ground wire form a closed-sum form?
When making PCB boards, the loop area is generally reduced in order to reduce interference. When laying the ground line, it should not be laid in a closed form, but it is better to arrange it in a branch shape, and the area of the ground should be increased as much as possible.
- How to adjust the routing topology to improve signal integrity?
This kind of network signal direction is more complicated, because for unidirectional, bidirectional signals, and different level types of signals, the topology influences are different, and it is difficult to say which topology is beneficial to the signal quality. And when doing pre-simulation, which topology to use is very demanding for engineers, and requires understanding of circuit principles, signal types, and even wiring difficulty.
