Microwave Tech - Anti-interference design of high frequency circuit board

Anti-interference design of high frequency circuit board

With the development of communication technology, wireless high-frequency circuit technology is used more and more widely. The performance indicators of high-frequency circuits directly affect the quality of the entire product. The layout and wiring of components can maximize the performance indicators of the circuit to achieve The purpose of anti-jamming design.

1. Layout of components
Since the surface mount chip generally uses infrared furnace heat flow welding to realize the welding of components, the layout of the components affects the quality of the solder joints, which in turn affects the yield of the product.
When designing high-frequency circuit PCBs, in addition to considering the layout of ordinary PCB design, how to reduce the mutual interference between various parts in the high-frequency circuit, how to reduce the interference of the circuit itself to other circuits, and the circuit itself Anti-interference ability.
The effect of the high-frequency circuit depends not only on the performance index of the high-frequency circuit board itself, but also largely depends on the mutual influence with the CPU processing board, so the layout is reasonable when designing the PCB. The general principle of the layout is that the components should be arranged in the same direction as much as possible, and the poor soldering phenomenon can be reduced or even avoided by selecting the direction of the PCB entering the soldering system;

Details in the layout:
1) First determine the position of the interface components with other PCB boards or systems on the PCB board, and you must pay attention to the coordination problems between the interface components (the direction of adding components, etc.);

2) Because the volume of the handheld products is very small, the arrangement of the components is very compact, so for the larger components, priority must be given to the corresponding position, and the mutual cooperation should be considered;
3) Carefully analyze the circuit structure, divide the circuit into blocks (add high-frequency amplifier circuits, mixing circuits, and demodulation circuits, etc.), separate strong and weak electrical signals as much as possible, and separate digital signal circuits from analog signal circuits, The circuits that complete the same function should be arranged within a certain range as much as possible to reduce the signal loop area; the filter network of each part of the circuit must be connected nearby, which can not only reduce the radiation height, but also reduce the probability of interference. Improve the anti-interference ability of the circuit;

4) Groups are grouped according to the different electromagnetic compatibility sensitivity of the unit circuits in use.

2. Wiring
After the layout of the components is basically completed, the wiring can be started. The basic principle of wiring is: When the assembly density permits, try to choose low-density wiring design, and the signal wiring is as thick as possible, which is conducive to impedance matching.

When designing the high-frequency circuit PCB, comprehensively consider the direction, width, and line spacing of the signal line, and make reasonable wiring. When wiring, keep all traces away from the border of the PCB board by about 2 mm, so as to avoid wire breakage or hidden dangers when the PCB board is made.

The power line should be as wide as possible to reduce loop resistance, and at the same time, make the direction of the power line and ground line consistent with the direction of data transmission to improve the anti-interference ability; the signal line should be as short as possible, and the number of vias should be minimized; The shorter the wiring between the components, the better, to reduce the distribution parameters and mutual electromagnetic interference; the incompatible signal lines should be as far away as possible from each other, and try to avoid parallel wiring, and the signal lines on both sides They should be perpendicular to each other; when wiring, an angle of 135° should be used where corners are needed, avoid turning at right angles.