25 simple high speed PCB design tips

1.PCB clock frequency more than 5MHZ or signal rise time less than 5ns, generally need to use multi-layer design.

Reason: Using multilayer board design signal loop area can be well controlled.

2. For the multilayer board, the key wiring layer (the layer where the clock line, bus, interface signal line, RF line, reset signal line, chip selection signal line and various control signal lines are located) should be adjacent to the complete ground plane, preferably between the two planes.

Reason: The key signal lines are generally strong radiation or extremely sensitive signal lines. Wiring near the ground plane can reduce the area of its signal loop, reduce its radiation intensity or improve anti-interference ability.

3. For single-layer boards, both sides of key signal cables should be covered with ground.

Reason: The ground covering on both sides of the key signal can reduce the area of the signal loop on the one hand and prevent crosstalk between the signal line and other signal lines on the other hand.

4. For the Double Layer PCB , the projection plane of the key signal line is paved with a large area, or the same as the single panel is covered with holes.

Cause: The key signals of the multilayer board are close to the same ground plane.

5. In the multilayer board, the power plane should shrink by 5H-20H relative to its adjacent ground plane (H is the distance between the power supply and the ground plane).

Reason: The retraction of the power plane relative to its return plane can effectively suppress the edge radiation problem.

6. The projection plane of the wiring layer shall be in the area of its return plane layer.

Reason: If the wiring layer is not in the projection area of the return plane layer, it will lead to the edge radiation problem, and lead to the increase of signal loop area, which leads to the increase of differential mode radiation.

7. The TOP and BOTTOM layers of a multilayer board have no signal cables larger than 50MHZ.

Reason: It is best to walk high frequency signals between two flat layers to inhibit their radiation to space.

8. For boards with a working frequency greater than 50MHz, if the second and penultimate layers are wiring layers, the TOP and BOOTTOM layers should be grounded copper foils.

Reason: It is best to walk high frequency signals between two flat layers to inhibit their radiation to space.

9. In multilayer boards, the single board main working power plane (the most widely used power plane) shall be adjacent to its ground plane.

Cause: Adjacent power plane and ground plane can effectively reduce the power circuit area.

10. In a single-layer board, there must be a ground cable adjacent to and parallel to the power supply.

Cause: The area of the power supply current loop is reduced.

11. In a double-layer board, there must be a ground wire adjacent to and parallel to the power supply.

Cause: The area of the power supply current loop is reduced.

12 In hierarchical design, avoid setting adjacent wiring layers. If adjacent wiring layers cannot be avoided, the spacing between the two wiring layers should be widened appropriately to narrow the spacing between the wiring layer and its signal loop.

Cause: Parallel signal routing on adjacent wiring layers may cause signal crosstalk.

13. Adjacent plane layers should avoid overlapping their projection planes.

Reason: When the projections overlap, the coupling capacitance between layers will cause the noise between layers to be coupled to each other.

14.PCB layout design, should fully comply with the design principle of straight line along the signal flow direction, try to avoid circling back and forth.

Reason: Avoid direct signal coupling, affecting signal quality.

15. When multiple module circuits are placed on the same PCB, digital circuits and analog circuits, high speed and low speed circuits should be arranged separately.

Reason: To avoid interference between digital circuit, analog circuit, high speed circuit and low speed circuit.

16. When high, medium, and low speed circuits exist on the circuit board, keep the high and medium speed circuits away from the interface.

Cause: To avoid high-frequency circuit noise radiating outward through the interface.

17. Energy storage and high-frequency filtering capacitors should be set near unit circuits or devices with large current changes (such as input and output terminals of power modules, fans and relays).

Reason: The existence of energy storage capacitor can reduce the circuit area of large current circuit.

18. The filter circuit of the circuit board power input port should be placed close to the interface.

Cause: To avoid the coupling of the already filtered lines.

19. On the PCB board, the filter, protection and isolation devices of the interface circuit should be placed close to the interface.

Reason: It can effectively realize the effect of protection, filtering and isolation.

20. If the interface has both a filter and a protection circuit, the protection before filtering principle should be followed.

Reason: The protective circuit is used for external overvoltage and overcurrent suppression. If the protective circuit is set after the filter circuit, the filter circuit will be damaged by overvoltage and overcurrent.

21. The layout should ensure that the input and output lines of the filter circuit (filter), isolation and protection circuit are not coupled with each other.

Cause: When the input and output of the above circuit are coupled with each other, the filtering, isolation or protection effect is weakened.

22. If the interface "clean" is designed on the board, the filtering and isolation devices should be set on the isolation belt between the "clean" and the working ground.

Reason: To avoid filtering or isolating devices through the plane layer coupling, weakening the effect.

23. "Cleanly", no devices other than filtering and protective devices shall be placed.

Reason: The purpose of "clean" design is to ensure that the interface radiation is minimal, and "clean" is easily coupled by external interference, so "clean" do not have other unrelated circuits and devices.

24. Strong radiation devices such as crystal, crystal oscillator, relay and switching power supply are at least 1000mil away from the interface connector of the board.

Reason: The interference will directly radiate outward or coupled current on the outgoing cable to radiate outward.

25. Sensitive circuits or devices (such as reset circuits) should be at least 1000mil away from the edges of the board, especially the interface side of the circuit board.

Reason: Similar to the circuit board interface and other places are most easily coupled by external interference (such as electrostatic), such as reset circuit, sensitive circuit is easy to cause misoperation of the system.