PCB board and high-frequency interference

How to choose a PCB board?
The selection of PCB boards must strike a balance between meeting design requirements and large-scale production and cost.The design requirements include electrical and mechanical parts.When designing very high-speed PCB boards(with frequencies greater than GHz),this material issue is usually more important.For example,the dielectric loss of commonly used FR-4 materials at several GHz frequencies will have a significant impact on signal attenuation,which may be inappropriate.In terms of electricity,attention should be paid to whether the dielectric constant and dielectric loss are compatible with the design frequency.
How to avoid high-frequency interference?
The basic idea of avoiding high-frequency interference is to minimize the electromagnetic interference of high-frequency signals,known as crosstalk.You can increase the distance between the high-speed signal and the analog signal,or add a ground protection/shunt trace next to the analog signal.In addition,attention should also be paid to the noise interference of digital grounding on analog grounding.
How to solve the signal integrity problem in high-speed design?
The integrity of the signal is a matter of impedance matching.The factors that affect impedance matching include the structure and output impedance of the signal source,the characteristic impedance of the channel,the characteristics of the load end,and the topology of the channel.The solution is to rely on topology terminals and adjust wiring.
How to handle some theoretical conflicts in actual wiring
Basically,dividing and isolating analog/digital grounding is correct.It should be noted that signal traces should not pass through separate areas(moats)as much as possible,and the return current path of power and signal should not be too large.
2.A crystal oscillator is an analog positive feedback oscillation circuit.In order to have a stable oscillation signal,it must meet the loop gain and phase specifications.The oscillation characteristics of this analog signal are easily disturbed.Even if traces of grounding protection are added,it may not be possible to completely isolate interference.If the distance is too far,the noise on the ground plane can also affect the positive feedback oscillation circuit.Therefore,the distance between the crystal oscillator and the chip must be as close as possible.
There are indeed many conflicts between high-speed wiring and electromagnetic interference requirements.But the basic principle is that the increased resistance,capacitance,or ferrite beads caused by electromagnetic interference will not cause certain electrical characteristics of the signal to deviate from specifications.Therefore,it is best to use track arrangement and PCB stacking technology to solve or reduce EMI problems,such as high-speed signals entering the inner layer.Finally,the resistance capacitance method or ferrite magnetic bead method is used to reduce signal damage.