Many customers often ask: What problems are often encountered in PCB circuit board design? Let professional PCB manufacturers tell you below.
1. Why try not to split across the power supply when wiring?
Because after the signal crosses different power layers, its return path becomes longer and is susceptible to interference. Of course, it is possible for low-speed signals, but for high-speed signals, it is necessary to carefully check and try not to cross.
2. Some boards have external input and output interfaces.
If the grounding of them is not well designed, it will affect the normal operation and become a source of external electromagnetic interference, sending the noise inside the board to the outside. Generally speaking, an independent interface ground is divided separately, and the connection with the signal ground is connected by a thin wire, and a resistor of O ohm or small resistance can be connected in series.
3. Common ground symbols:
PE, PGND, FG-protection ground or chassis; GND-working ground; DGND-digital ground; AGND-analo ground; LGND-lightning protection ground.
4. How to choose the PCB board?
The choice of PCB board must strike a balance between meeting the design requirements, mass production and cost. Design requirements contain both electrical and mechanical components. As far as electricity is concerned, it is necessary to pay attention to whether the dielectric constant and dielectric loss are suitable for the designed frequency.
5. How to avoid high frequency interference?
The basic idea is to minimize the interference of the high-frequency signal electromagnetic field, which is the so-called crosstalk. The distance between the high-speed signal and the analo signal can be widened; also pay attention to the noise interference of the digital ground to the analo ground.
6. Why should the wiring of differential pairs be properly close and parallel?
The so-called proper proximity is because this spacing will affect the value of the differential impedance, which is an important parameter for designing a differential pair. The need for parallelism is also due to the need to maintain the consistency of the differential impedance. If the two lines are far and near, the differential impedance will be inconsistent, which will affect signal integrity and time delay.
7. Will adding test points affect the quality of high-speed signals?
It depends on the method of adding test points and how fast the signal is. Basically, additional test points may be added to the line or pulled from a small line. The former is equivalent to adding a small capacitor on the line, while the latter is an extra branch. These two situations will affect the high-speed signal more or less, and the degree of influence is related to the frequency speed of the signal and the rate of change of the signal edge.
