5 Techniques to Design High-frequency PCB

1. Use the wire lead between the pins as short as possible

The radiation intensity of the signal is proportional to the length of the signal line. The longer the lead of the high-frequency signal, the easier it is to couple to the element close to it. The device goes up, so for high-frequency signal lines such as signal clock, crystal oscillator, DDR data, LVDS line, USB line, HDM line, etc., it is required that the traces as short as possible are as short as possible.

2. Use as few bendings as possible in wire lead
It is best to use a full straight line for the wiring of the high-frequency circuit board, and it needs to be turned. It can be turned by a 45-degree broken line or a circular arc. This requirement is only used to improve the fixing strength of the high-frequency circuit board in the high-frequency circuit board. , Meeting this requirement can reduce the external emission and mutual coupling of high-frequency signals.

3. Isolate the ground wire of the high-frequency digital signal from the ground wire of the analog signal

When the analog ground wire, digital ground wire, etc. are connected to the public ground wire, use high-frequency choke magnetic beads to connect or directly isolate and select a suitable place for single-point interconnection. The ground potential of the ground wire of the high-frequency digital signal is generally inconsistent. There is often a certain voltage difference between the two directly. Moreover, the ground wire of the high-frequency digital signal often contains very rich harmonic components of the high-frequency signal. When the digital signal ground wire and the analog signal ground wire are directly connected, the harmonics of the high-frequency signal will interfere with the analog signal through the ground wire coupling. Therefore, under normal circumstances, the ground wire of the high-frequency digital signal and the ground wire of the analog signal should be isolated, and the method of single-point interconnection at a suitable position can be adopted, or the method of interconnection by high-frequency choke magnetic beads can be used.

4. Avoid loops formed by wiring
All kinds of high-frequency signal traces should not form a loop as much as possible. If it is unavoidable, the loop area should be as small as possible.

5. The less the lead layer alternation between the pins of the high frequency circuit board device, the better.

The so-called “the less lead layer alternation is better” means that the fewer vias and vias used in the component connection process, the better. A via can bring about 0.5pF distributed capacitance, reducing the number of vias can significantly increase the speed and reduce the possibility of data errors.

6. Add a high-frequency decoupling capacitor to the power supply pin of the integrated circuit block.

Each power supply pin of the integrated circuit block adds a high-frequency decoupling capacitor nearby. Increasing the high-frequency decoupling capacitor of the power supply pin can effectively suppress the interference caused by high-frequency harmonics on the power supply pin