1: Closed-loop routing rules for high-speed signals

As the density of PCB boards becomes higher and higher, many PCB LAYOUT engineers are prone to make mistakes during the wiring process, that is, high-speed signal networks such as clock signals produce closed-loop results when routing multi-layer PCBs. , such a closed-loop result will produce a loop antenna, increasing the radiation intensity of EMI.

  2: Open-loop routing rules for high-speed signals

2. It is mentioned that the closed loop of high-speed signals will cause EMI radiation, but the open loop will also cause EMI radiation.

In high-speed signal networks such as clock signals, once an open loop occurs during multi-layer PCB routing, a linear antenna will be generated, increasing the radiation intensity of EMI.

Three: Characteristic impedance continuity rules of high-speed signals

For high-speed signals, the continuity of characteristic impedance must be ensured when switching between layers, otherwise EMI radiation will be increased. In other words, the width of wiring on the same layer must be continuous, and the impedance of wiring on different layers must be continuous.

Four: Topology rules in high-speed PCB design

In high-speed PCB design, the control of the circuit board's characteristic impedance and the design of the topology under multiple loads directly determine the success or failure of the product.

The diagram shows a daisy chain topology, which is generally beneficial when operating at several Mhz. In high-speed PCB design, it is recommended to use a back-end star symmetrical structure.

  Five: Return path rules

All high-speed signals must have good return paths. Try to ensure that the return path of high-speed signals such as clocks is as small as possible. Otherwise, the radiation will be greatly increased, and the size of the radiation is proportional to the area surrounded by the signal path and the return path.

6: Placement rules for decoupling capacitors of devices

The placement of the decoupling capacitor is very important. Unreasonable placement will not achieve the decoupling effect at all. The principle is: be close to the pins of the power supply, and the area surrounded by the power supply traces and ground wires of the capacitor is the smallest.

PCB EMI Design Specifications

1: Closed-loop routing rules for high-speed signals

As the density of PCB boards becomes higher and higher, many PCB LAYOUT engineers are prone to make mistakes during the wiring process, that is, high-speed signal networks such as clock signals produce closed-loop results when routing multi-layer PCBs. , such a closed-loop result will produce a loop antenna, increasing the radiation intensity of EMI.

  2: Open-loop routing rules for high-speed signals

2. It is mentioned that the closed loop of high-speed signals will cause EMI radiation, but the open loop will also cause EMI radiation.

In high-speed signal networks such as clock signals, once an open loop occurs during multi-layer PCB routing, a linear antenna will be generated, increasing the radiation intensity of EMI.

  Three: Characteristic impedance continuity rules of high-speed signals

For high-speed signals, the continuity of characteristic impedance must be ensured when switching between layers, otherwise EMI radiation will be increased. In other words, the width of wiring on the same layer must be continuous, and the impedance of wiring on different layers must be continuous.

Four: Topology rules in high-speed PCB design

In high-speed PCB design, the control of the circuit board's characteristic impedance and the design of the topology under multiple loads directly determine the success or failure of the product.

The diagram shows a daisy chain topology, which is generally beneficial when operating at several Mhz. In high-speed PCB design, it is recommended to use a back-end star symmetrical structure.

Five: Return path rules

All high-speed signals must have good return paths. Try to ensure that the return path of high-speed signals such as clocks is as small as possible. Otherwise, the radiation will be greatly increased, and the size of the radiation is proportional to the area surrounded by the signal path and the return path.

6: Placement rules for decoupling capacitors of devices

The placement of the decoupling capacitor is very important. Unreasonable placement will not achieve the decoupling effect at all. The principle is: be close to the pins of the power supply, and the area surrounded by the power supply traces and ground wires of the capacitor is the smallest.