PCB design is an important link in the production of the entire PCB circuit board, which determines the basis of the entire PCB board. The following are some issues that need to be paid attention to in PCB design summarized by PCB circuit board manufacturers.
1. Select the PCB board
Choosing a PCB board must strike a balance between meeting design requirements, mass production and cost. Design requirements include electrical and mechanical components. In terms of electricity, the design needs to focus on whether the frequency of the dielectric constant and dielectric loss is consistent.
2. Avoid high frequency interference
The basic idea of avoiding high-frequency interference is to minimize the interference of the electromagnetic field of high-frequency signals, that is, crosstalk.
3. Solve the signal integrity problem
Basically a matter of impedance matching. Factors that affect impedance matching include the signal source architecture and output impedance, the characteristic impedance of the trace, the characteristics of the load terminal, and the topology of the trace.
4. Realize differential wiring
There are two things to note about the wiring of the differential pairs. One is that the length of the two lines should be as long as possible, and the other is that the spacing between the two lines (determined by the differential impedance) should remain the same, that is, remain parallel.
5. Perform differential routing when there is only one output clock signal line
To use differential routing, therefore, differential routing cannot be used for clock signals with only one output.
6. Matching resistance between differential pairs at the receiving end
Usually, a matching resistor is added between the differential pairs at the receiving end, and its value should be equal to the value of the differential impedance. This way the signal quality will be better.
7. The wiring of the differential pair should be closely parallel
The wiring of the differential pair should be properly closed and parallel. The proper proximity is because this spacing affects the value of the differential impedance, which is an important parameter in designing a differential pair. Parallelization is also required because of the consistency of the differential impedance.
8. Deal with some theoretical conflicts in actual wiring
(1) Basically, isolating analo/digital partitions is correct. The signal trace should not cross the divided area as far as possible, and the return current path of the power supply and signal should not be too large.
(2) The crystal oscillator is an analo positive feedback oscillator circuit. In order to obtain a stable oscillating signal, the loop gain and phase specifications must be met. Therefore, the distance between the crystal and the chip must be very close.
