What are the key points in PCB design?

　　1. Select PCB board

　　The selection of PCB boards must strike a balance between meeting design requirements and achieving mass production and cost. The design requirements include two parts: electrical and mechanical. This material issue is usually important when designing very high-speed PCB boards (frequencies greater than GHz). For example, the commonly used FR-4 material may not be suitable as its dielectric loss at several GHz frequencies can have a significant impact on signal attenuation. In terms of electrical performance, attention should be paid to whether the dielectric constant and dielectric loss are used together at the designed frequency.

　　2. Avoiding high-frequency interference

　　The basic idea to avoid high-frequency interference is to minimize the interference of high-frequency signal electromagnetic fields, also known as crosstalk. You can widen the distance between the high-speed signal and the analog signal, or add ground guard/hunt traces next to the analog signal, and also pay attention to the noise interference of the digital ground on the analog ground.

　　3. Addressing signal integrity issues

　　Signal integrity is essentially an issue of impedance matching. The factors that affect impedance matching include the architecture and output impedance of the signal source, the characteristic impedance of the wiring, the characteristics of the load end, and the topology architecture of the wiring. The solution is to rely on the topology of termination and adjustment of wiring.

　　4. Implement differential distribution line method

　　There are two points to note in the wiring of differential pairs: first, the length of the two lines should be as long as possible, and second, the distance between the two lines (determined by the differential impedance) should be kept constant, that is, parallel. There are two parallel ways, one is for two lines to run on the same side by side layer, and the other is for two lines to run on adjacent layers above and below (over under). Generally, there are many ways for the former to implement side by side.