PCB (printed circuit board) boards, known as the "mother of electronic products," are a key foundational element in the entire electronic product industry chain. With the rapid development of downstream application fields such as IoT technology, automotive electronics, and 5G communication, the PCB market, including high-frequency PCBs, has broad development space in China. Today, you will learn what high-frequency PCBs are; the important parameters of high-frequency PCBs, and why it is necessary to measure the signal integrity of PCBs? The testing requirements for high-speed signal integrity, common testing items include time domain, frequency domain, eye diagram, etc.

When processing and testing high-frequency PCBs and high-frequency antennas, beginners often encounter unsatisfactory product results due to selecting the wrong high-frequency PCB. Today, let's briefly discuss what types of high-frequency PCB materials are available and how to choose them.

High-frequency circuit boards refer to special circuit boards with high electromagnetic frequencies, which are among the more difficult types of materials. So, what aspects should be considered when designing high-frequency circuit boards?

1. Consider how to avoid high-frequency interference? Avoiding high-frequency interference means minimizing the electromagnetic field interference of high-frequency signals, also known as crosstalk. You can increase the distance between high-speed signals and analog signals, and also pay attention to the noise interference from digital ground to analog ground.

2. Consider how to choose PCB materials? Choosing PCB materials must strike a balance between meeting design requirements, manufacturability, and cost. Design requirements include both electrical and mechanical aspects.

3. How to solve the signal integrity problem? Signal integrity is essentially an impedance matching issue. The solution relies on termination and adjusting the topology of the traces.

4. For a clock signal line with only one output, how to achieve differential routing? Using differential routing only makes sense if both the signal source and the receiving end are differential signals, so differential routing cannot be used for a clock signal with only one output.

5. How to achieve differential routing? First, the lengths of the two lines should be as equal as possible, and the spacing between the two lines (determined by differential impedance) should remain constant, meaning they should stay parallel. There are two ways to maintain parallelism: one is to have both lines on the same routing layer, and the other is to have both lines on two adjacent layers.

6. Should a matching resistor be added between the receiving end differential pairs? A matching resistor is usually added between the receiving end differential pairs, and its value should equal the differential impedance value, which will improve signal quality.

7. Why should the routing of differential pairs be close and parallel? The so-called appropriate closeness is because this spacing affects the value of the differential impedance, which is an important parameter in designing differential pairs. They need to be parallel to maintain the consistency of the differential impedance.

8. How to handle some theoretical conflicts in actual routing?

Basically, it is correct to isolate the analog and digital grounds. It is important to ensure that signal traces do not cross over the isolated areas, and also to avoid making the return current path of the power supply and signal too large.