Design process of high frequency PCB circuit

For high frequency circuits, the rationality of routing affects the performance of the circuit directly.


In the design of high frequency circuit lines, we must pay attention to the following points in order to obtain the high frequency circuit characteristics:


1, the high-frequency impedance of the earth.

2, the inductance of the line.

3, high frequency coupling between circuits.


First, the high frequency impedance of the ground should be reduced as much as possible


In low frequency circuit, one point grounding is adopted to make each earthing point become same potential. In high frequency circuits, each circuit must also have the same potential at each point of the circuit.


But in high frequency circuit, it is difficult to reach one point because of long line. Therefore, it is important to reduce the impedance value of the ground so that the potential of each site is the same as possible.


Two, the inductance of the line will be greatly reduced


In a high frequency circuit, the wire connecting the components has an inductance component. The wiring components with higher sense of Changsha, will cause the degradation of the frequency characteristic (the formation of low pass filter components and stray capacitance), may also occur oscillation (due to inductance components of the phase deviation).


Therefore, in principle, the line should be coarse and short, and the arrangement of components should be carried out according to this principle. And pins, resistors, capacitors and other components of the terminal has inductance components, when the frequency is very high, can not be ignored. Therefore, the terminals of the components should be shortened as much as possible. SMD devices are best used in high frequency circuits to reduce inductance at the component terminals.


Three, to prevent high-frequency coupling between the circuits


The higher the signal frequency and the shorter the filter length, the easier it becomes to launch the electromagnetic wave into the air. Therefore, for the signals on dozens of MHz, most of the copper or tin iron sheet should be used to isolate the circuit, so as to prevent high frequency coupling between the internal and external of the circuit. In the same circuit, in order to prevent the coupling in the circuit, the isolation method can also be adopted, and the isolation cover can be grounded, and the ground impedance can also be reduced. In addition, an inductor or a magnetic ring is connected on the power supply line, and a through capacitor can be added to prevent the high frequency coupling through the power supply line.


 

(Source: internal information)

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