skills of PCB layout

3. Power cord design   

According to the size of the printed circuit board current, try to increase the width of the power line to reduce the loop resistance. At the same time, make the direction of the power line and ground line consistent with the direction of data transmission, which helps to enhance the ability to resist noise. In single-sided or double-sided boards, if the power line is very long, decoupling capacitors should be added to the ground every 3000 mils. The value of the capacitor is 10uF + 1000pF.



4. Ground design   

The principle of ground design is:   

(1) Separate digital ground and analog ground. If there are both logic circuits and linear circuits on the circuit board, they should be separated as much as possible. The ground of the low-frequency circuit should use single-point parallel grounding as much as possible. When the actual wiring is difficult, it can be partially connected in series and then connected in parallel. High-frequency circuits should be grounded with multiple points in series, the ground wire should be short and leased, and grid-like large-area ground foil should be used around the high-frequency components.  


(2) The ground wire should be as thick as possible. If the grounding wire uses a very strong line, the grounding potential changes with the change of current, which reduces the anti-noise performance. Therefore, the grounding wire should be thickened so that it can pass three times the allowable current on the printed board. If possible, the ground wire should be above 2~3mm.  


(3) The ground wire constitutes a closed loop. The printed circuit board composed only of digital circuits, the ground circuit is arranged in a group of loops, most of which can improve the ability to resist noise.


5. Signal line design

For key signal lines, if the board has an internal signal routing layer, key signal lines such as clocks are laid on the inner layer, and the wiring layer is preferred. In addition, the key signal lines must not be routed across the partition, including the reference plane gap caused by vias and pads, otherwise it will cause an increase in the signal loop area. And the key signal line should be 3H away from the edge of the reference plane (H is the height of the line from the reference plane) to suppress the edge radiation effect.


For sensitive signal lines such as clock lines, bus lines, radio frequency lines and other strong radiation signal lines, reset signal lines, chip selection signal lines, system control signals, etc., they should be far away from the outgoing signal lines of the interface. Therefore, the interference of the strong radiation signal line is prevented from being coupled to the outgoing signal line and radiating outward; and the external interference brought in by the outgoing signal line of the interface is prevented from being coupled to the sensitive signal line, causing the system to malfunction.


For differential signal lines, they should be of the same layer, equal length, and parallel running lines, keeping the impedance consistent, and no other routing between the differential lines. Because the common-mode impedance of the differential pair is equal, its anti-interference ability can be improved. According to the above wiring rules, the typical printed circuit board circuit of the air conditioner is improved and optimized