PCB Technical - Layout and wiring principle of RF PCB

As a tasteful PCB Design Engineer, we must have known the layout and wiring rules of general PCB. However, do you all know the design rules of RF PCB?

Today, ipcb, let's talk about the layout and wiring principles of RF PCB

RF PCB

Layout principle ofRF PCB

1. Layout determination: before layout, the function of single board, working frequency band, current and voltage, main types of RF devices, EMC, relevant RF indicators, etc. shall be understood in detail, and the laminated structure, impedance control, overall structure size, size and position of shielding cavity and cover, processing instructions of special devices (such as the size and position of devices requiring hollowing and direct shell heat dissipation) shall be clarified.

In addition, the power, heat dissipation, gain, isolation, sensitivity and other indicators of main RF devices as well as the connection of filtering, bias and matching circuits should be specified. For power amplifier circuits, the matching wiring requirements recommended in the device manual or the impedance matching circuit guidance obtained from the simulation of RF field analysis software should be obtained.

2. Physical partition: the key is to arrange the main components according to the main signal flow direction of the single board. First, fix the components on the RF path according to the RF port position, and adjust their orientation to reduce the length of the RF path to.

In addition to considering the general layout rules, it is also necessary to consider how to reduce the mutual interference and anti-interference ability of various parts to ensure that multiple circuits have sufficient isolation. For circuit modules with insufficient isolation or sensitive isolation and strong radiation source, metal shielding cover should be used to shield RF energy in RF area.

3. Electrical Zoning: the layout is generally divided into three parts: power supply, digital and analog, which should be separated in space, and the layout and wiring should not cross the region. The strong current and weak current signals should be separated as far as possible, and the digital and analog signals should be separated. The circuits to complete the same function should be arranged in a certain range as far as possible, so as to reduce the signal loop area.

Wiring principle of RF PCB

4. Keep the digital circuit away from the analog circuit as far as possible, ensure that the RF wiring refers to a large area of ground plane, and the RF line is on the surface as far as possible.

5. Digital and analog signal lines do not cross area wiring. If RF wiring must pass through signal lines, it is preferred to lay a layer of ground connected to the main ground along the RF wiring; secondary selection ensures that the RF line and signal line cross each other, which can reduce the capacitive coupling. At the same time, try to lay more ground around each RF line and connect to the main ground.

In general, the RF printed wire should not be parallel wiring and should not be too long. If parallel wiring is really needed, a ground wire should be added between the two wires (the ground wire is perforated to ensure good grounding). RF differential line, parallel line, two parallel lines are added with ground wire (the ground wire is perforated to ensure good grounding). The characteristic impedance of printed wire is designed according to the requirements of the device.

6. The basic sequence of RF PCB wiring is: RF line - baseband RF interface line (IQ line) - clock line - power supply part - digital baseband part - ground.

7. Considering the influence of green oil on the performance and signal of microstrip lines, it is suggested that green oil should not be applied to high frequency single board microstrip lines, and green oil should be applied to medium and low frequency single board microstrip lines.

8. RF wiring is usually not perforated. If it is necessary to change the RF wiring layer, the via size should be reduced to, which can not only reduce the path inductance, but also reduce the chance of RF energy leakage to other areas in the laminate.

9. There are always multiple RF / if signals interfering with each other in duplexer, if amplifier and mixer. RF and if wiring should be crossed as far as possible, and a piece of ground should be separated between them.

10. Except for special purposes, it is forbidden to extend the redundant ends of RF signal wiring.

11. The baseband RF interface line (IQ line) should be wider than 10mil. In order to avoid phase error, the line length should be equal as much as possible, and the spacing should be equal as much as possible.

12. The RF control line should be as short as possible, and the wiring length should be adjusted according to the input and output impedance of the transmission control signal device to reduce the introduction of noise. The wiring is far away from RF signal, nonmetallic hole and "ground" edge. Do not drill ground vias around the wiring to prevent the signal from coupling to the RF ground through the via.

13. As far as possible, the digital wiring and power wiring should be far away from the RF circuit; clock circuit and high frequency circuit are the main interference and radiation sources, so they must be arranged separately and away from the sensitive circuit.

14. The wiring of the master clock shall be as short as possible. The line width is recommended to be more than 10mil. The ground shall be wrapped on both sides of the wiring to prevent interference from other signal lines. It is recommended to use stripline for wiring.

15. The control line of voltage controlled oscillator (VCO) must be far away from RF signal. If necessary, the control line of VCO can be processed by packet grounding.