What are the anti-interference design measures for PCB circuits?
1. 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 the ground line consistent with the direction of data transmission.
2. The principle of ground wire design
(1) The digital ground is separated from the 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 be grounded in parallel at a single point as much as possible. If the actual wiring is difficult, it can be partially connected in series and then grounded in parallel. The high-frequency circuit should be grounded at multiple points in series, the ground wire should be short and leased, and the grid-like large-area ground foil should be used around the high-frequency component as much as possible.
(2) The grounding wire should be as thick as possible. If possible, the grounding wire should be 2~3mm or more.
(3) The ground wire forms a closed loop. For printed boards composed only of digital circuits, most of their grounding circuits are arranged in loops to improve noise resistance.
3. Decoupling capacitor configuration
The general configuration principles of decoupling capacitors are:
(1) Connect a 10~100uf electrolytic capacitor across the power input. If possible, it is better to connect to 100uF or more.
(2) In principle, each integrated circuit chip should be equipped with a 0.01pF ceramic capacitor. If the gap of the printed board is not enough, a 1-10pF tantalum capacitor can be arranged for every 4~8 chips.
(3) For devices with weak anti-noise capability and large power supply changes when turned off, a decoupling capacitor should be directly connected between the power line and the ground line of the chip.
(4) Capacitor leads should not be too long, especially for high-frequency bypass capacitors.
(5) When there are contactors, relays, buttons and other components in the printed board. Large spark discharge will occur during operation, and RC circuit must be used to absorb the discharge current. Generally, R is 1~2K, and C is 2.2~47UF.
(6) The input impedance of CMOS is very high and it is susceptible to induction, so when in use, the unused terminal should be grounded or connected to a positive power supply.
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