PCB and circuit anti-interference measures

Printed circuit board (PCB) is a support for circuit components and devices in electronic products. It provides electrical connections between circuit components and devices. With the rapid development of electric technology, the density of PGB is higher and higher. The quality of PCB design has a great influence on anti-interference ability, so the design of PCB should accord with the requirement of anti-interference design.

The anti-interference design of printed circuit board is closely related to the specific circuit. Here, some common measures of PCB anti-interference design are explained.

1. power cord design

According to the printed circuit board current size, as far as possible leased power line width, reduce loop resistance. Simultaneous. Make the power cord. The direction of the ground wire is consistent with the direction of data transmission, which helps to improve the noise immunity.

2. lot design

Ground design is the principle of:

(1) separate from analog to digital. If there are logic circuits and linear circuits on the circuit board, they should be separated as far as possible. The low frequency circuit should try to adopt single point parallel connection, and when the actual wiring is difficult, it can be connected in series and connected again. The high frequency circuit should adopt multi-point series grounding, the ground wire should be short and leased, and the high frequency components shall be covered with grid like large area foil as far as possible.

(2) grounding wire should be as bold as possible. If the ground with a sewing line, then the ground potential change with the current change, the anti noise performance decreased. Therefore, the ground wire should be thickened so that it can pass three times the permissible current on the printed board. If possible, the grounding wire shall be above 2~3mm.

(3) the grounding wire forms the closed loop. A printed circuit board consisting of a digital circuit, whose grounding circuit is made up of a group loop, can largely improve the noise immunity.

3. decoupling capacitor configuration

One of the conventional practices in PCB design is the appropriate decoupling capacitor at each key part of the printed circuit board. The general configuration of the decoupling capacitor is that:

(1) the electrolytic capacitor of the power input terminal is connected to 10~100uf. If possible, connect 100uF or better.

(2) each chip integrated circuit principle should be arranged in a 0.01pF ceramic capacitor, such as printed circuit board space enough, every 4~8 chip layout of a 1~10pF capacity.

(3) the ability to resist noise is weak. When switching off, a device with large power change, such as a RAM.ROM memory device, shall be connected directly between the power line of the chip and the ground wire to return the lotus root capacitance.

(4) the capacitor lead can not be too long, especially the high frequency bypass capacitor can not have lead. In addition, we should also pay attention to the following two points:

(1 there is a contactor in the printed board. Relay。 When the button and other components are in operation, a larger spark discharge will be produced when they are operated, and the discharge current must be absorbed by the RC circuit shown in the drawings. General R, take 1~2KC, take 2.2~47UF.

(2CMOS the input impedance is very high and sensitive to induction, so when it is in use, it is not necessary to connect the ground or to the positive power supply