Dec. 12, 2019
All of these require designers to have certain practical experience and engineering design capabilities, but to have these capabilities, each designer in PCB fabrication factory cannot be achieved overnight, only to learn from other people's experience, plus their own constant exploration and thinking, To keep improving. This article summarizes some of the design experience in the work, which is conducive to improving the anti-interference ability of the RF circuit PCB and helping beginners in RF circuit design to avoid unnecessary detours.
The overall requirements for wiring are: short and straight RF signal traces, reducing line abruptness, making fewer vias, not intersecting with other signal lines, and adding as many vias as possible around the RF signal line.
Here are some common optimizations:
3.1 Gradient line processing
In the case where the RF line width is larger than the width of the IC device pins, the line width of the contact chip is gradually changed.
3.2 Arc line processing
When the RF line cannot be straight, do the arc line processing, which can reduce the external radiation of RF signal and the mutual coupling between them. Some experiments have proved that the corners of the transmission line use curved right angles, which can minimize the return loss.
3.3 Ground and Power
The ground wire is as thick as possible. Under conditions, every layer of the high TG PCB should be grounded as much as possible, and the ground should be connected to the main ground. Make more ground vias to reduce the impedance of the ground wire as much as possible.
The power of the RF circuit should not be split as much as possible. The entire power plane not only increases the radiation of the power plane to the RF signal, but also is easily interfered by the RF signal. Therefore, the power line or plane generally adopts a long shape, and is processed according to the magnitude of the current. It is as thick as possible on the premise of meeting the current capacity, but it cannot be widened unlimitedly. Avoid loops when handling power lines.
The direction of the power and ground wires must be parallel to the direction of the RF signal but should not overlap. Where there is a cross, it is best to use a vertical cross.
3.4 Cross processing
The RF and IF signal traces cross each other, and ground as far as possible between them. When the RF signal crosses other signal traces, try to arrange a ground connected to the main ground along the RF trace between them. If it is not possible, make sure they are crisscross. Other signal traces here also include power lines.
High Frequency PCB
3.5 Land treatment
The RF signal, the interference source, the sensitive signal and other important signals are processed in a grounded manner, so that the anti-interference ability of the signal can be improved and the interference of the signal to other signals can be reduced.
RF cables on the same layer should be grounded and ground vias should be added to the ground copper. The hole spacing should be less than 1/20 of the wavelength (λ) corresponding to the signal frequency. The width of the copper-clad copper sheet is 2W or 3H from the RF line, where H represents the total thickness of the adjacent dielectric layer.