The feed inductance of the bias circuit is placed perpendicular to the RF channel, as shown in Figure 6, mainly to avoid mutual inductance between inductive devices.
The same modules should be made into the same layout or symmetrical layout as much as possible, as shown in Figure 4 and Figure 5. In addition, when using an L-shaped or U-shaped layout, the turning point should not turn as soon as it enters the interface, as shown on the left in Figure 3, but after a slight straight line, as shown on the right in Figure 3. When it is unavoidable, it’d be better to increase the distance between input and output to at least 1.5cm. It’d be better not to use U-shaped layout (as shown in Figure 2).
At this time, L-shaped layout can be used. However, due to the limitation of PCB board and cavity space, it cannot be laid out in a straight shape in many cases. The components of the RF main signal are arranged in a straight line as much as possible, as shown in Figure 1. The following techniques are often used in the layout. The signal is far away from high-speed digital signals and RF signals. By adjusting its direction, the length of the RF path is minimized, and the input is far away from the output, and the high-power circuit and the low-power circuit are separated as far as possible. The key to the layout of components is to fix the components on the RF path. What we discussed here is the layout of the components of the multilayer board. From the perspective of PCB LAYOUT, this article provides some processing skills, which are of great use to improving the anti-interference ability of radio frequency circuits.
Because of this, how to weigh the pros and cons in the PCB design process to find a suitable compromise, to reduce these interferences as much as possible, and even to avoid the interference of some circuits, is the key to the success or failure of the RF PCB design.
Because the radio frequency (RF) circuit is a distributed parameter circuit, skin effect and coupling effect are prone to occur in the actual work of the circuit, so in the actual PCB design, it will be found that the interference radiation in the circuit is difficult to control, Such as: mutual interference between digital circuit and analog circuit, noise interference of power supply, interference caused by unreasonable ground wire, etc.