In the design of PCB board, with the rapid increase of frequency, there will be a lot of interference which is different from the design of low-frequency PCB board. There are mainly four aspects of interference, including power supply noise, transmission line interference, coupling and electromagnetic interference (EMI).

How to solve the interference of high-frequency PCB design

I. There are several methods to eliminate power supply noise in PCB design

1. Pay attention to the through hole on the board: the through hole makes the power supply layer need to etch the opening to leave space for the through hole through. If the opening of the power supply layer is too large, it is bound to affect the signal loop, the signal is forced to bypass, the loop area increases, and the noise increases. At the same time, if several signal lines are clustered near the opening and share the same loop, the common impedance will cause crosstalk. See Figure 2.

How to solve the interference of high-frequency PCB design?

2. The connection line needs enough ground: each signal needs to have its own proprietary signal loop, and the loop area of the signal and loop is as small as possible, that is to say, the signal and loop should be parallel.

3. analog and digital power supply to separate: high-frequency devices are generally very sensitive to digital noise, so the two should be separated, connected together at the entrance of the power supply, if the signal across the analog and digital parts of the words, you can place a loop across the signal to reduce the loop area. The digital-analog span used for the signal loop.

How to solve the interference of high-frequency PCB design

4. Avoid overlapping of separate power supplies between different layers: otherwise, circuit noise can easily pass through parasitic capacitive coupling.

5.  isolation of sensitive components: such as PLL.

6. Place the power line: To reduce the signal loop, place the power line on the edge of the signal line to reduce the noise.

How to solve the interference of high-frequency PCB design?

Ii. Methods of eliminating transmission line interference in PCB design are as follows:

(a) Avoid impedance discontinuity of transmission line. The point of discontinuous impedance is the point of transmission line mutation, such as straight corner, through hole, etc., should be avoided as far as possible. Methods: To avoid straight corners of the line, as far as possible to go 45° Angle or arc, large Angle can also be; Use as few through holes as possible, because each through hole is an impedance discontinuity. Signals from the outer layer avoid passing through the inner layer and vice versa.

How to solve the interference of high-frequency PCB design？

(b) Do not use stake lines. Because any pile line is a source of noise. If the pile line is short, it can be connected at the end of the transmission line; If the pile line is long, it will take the main transmission line as the source and produce great reflection, which will complicate the problem. It is recommended not to use it.

3. There are several ways to eliminate crosstalk in PCB design

1. The size of the two kinds of crosstalk increases with the increase of load impedance, so the signal line sensitive to interference caused by crosstalk should be properly terminated.

2, as far as possible to increase the distance between signal lines, can effectively reduce capacitive crosstalk. Ground management, spacing between wiring (such as active signal lines and ground lines for isolation, especially in the state of jump between the signal line and ground to interval) and reduce lead inductance.

3. Capacitive crosstalk can also be effectively reduced by inserting a ground wire between adjacent signal lines, which must be connected to the formation every quarter wavelength.

4. For sensible crosstalk, the loop area should be minimized and, if allowed, the loop eliminated.

5. Avoid signal sharing loop.

6, pay attention to signal integrity: the designer should realize the end connection in the welding process to solve the signal integrity. Designers using this approach can focus on the microstrip length of the shielding copper foil in order to obtain good performance of signal integrity. For systems with dense connectors in the communication structure, the designer can use a PCB as the terminal.

4. There are several methods to eliminate electromagnetic interference in PCB design

1. Reduce loops: Each loop is equivalent to an antenna, so we need to minimize the number of loops, the area of loops and the antenna effect of loops. Make sure the signal has only one loop path at any two points, avoid artificial loops and use the power layer whenever possible.

2, filtering: in the power line and in the signal line can take filtering to reduce EMI, there are three methods: decoupling capacitor, EMI filter, magnetic components. EMI filter is shown in .

How to solve the interference of high-frequency PCB design？

3, shielding. As a result of the length of the issue plus a lot of discussion shielding articles, no longer specific introduction.

4, try to reduce the speed of high frequency devices.

5, increase the dielectric constant of PCB board, can prevent high frequency parts such as transmission line near the board from radiating outward; Increase the thickness of PCB board, minimize the thickness of microstrip line, can prevent electromagnetic line spillover, can also prevent radiation.