PCB Tech - Circuit board knowledge that high frequency pcb board must master

1. If the circuit system of the high-frequency PCB board design contains FPGA devices, the QuartusII software must be used to verify the pin assignment before drawing the schematic diagram. (Some special pins in FPGA cannot be used as ordinary IO).

2. The 4-layer boards of high-frequency PCB board/high-frequency board/high-frequency microwave radio frequency board from top to bottom are: signal plane layer, ground, power supply, signal plane layer; 6-layer board (high-frequency PCB board) from top From the bottom, they are: signal plane layer, ground, signal inner electric layer, signal inner electric layer, power supply, signal plane layer. For boards with 6 layers or more (the advantage is: anti-interference radiation), the internal electric layer wiring is preferred, and the plane layer is not allowed to go. It is forbidden to route the wiring from the ground or power layer (reason: the power layer will be divided, causing parasitic effects).

3. Wiring of multi-power supply system: If FPGA+DSP system is made of 6-layer board (high-frequency PCB board/high-frequency board/high-frequency microwave radio-frequency board), generally there will be at least 3.3V+1.2V+1.8V+5V.

1. 3V is generally the main power supply, and the power layer is directly laid, and the global power supply network is easily routed through the vias;

5V may generally be the power input, and only a small area of copper is required. And as thick as possible.

2. 2V and 1.8V are the core power supply (if you directly use the wire connection method, you will encounter great difficulties when facing BGA devices). Try to separate 1.2V and 1.8V during layout, and let the components connected within 1.2V or 1.8V The layout is in a compact area, and it is connected by copper.

In short, because the power supply network is spread over the entire high-frequency PCB board, if the wiring method is used, it will be very complicated and will go around a long distance. The method of laying copper is a good choice!

4. The wiring between adjacent layers adopts a cross method: it can reduce electromagnetic interference between parallel wires and facilitate wiring.

5. What is the isolation method for analog and digital isolation? Separate the devices used for analog signals from those used for digital signals during layout, and then cut across the AD chip across the board!

The analog signal is laid with an analog ground, and the analog ground/analog power supply and the digital power supply are connected at a single point through an inductor/magnetic bead.

6. High-frequency PCB board design based on high-frequency PCB board/high-frequency board/high-frequency microwave radio frequency board design software can also be regarded as a software development process. Software engineering pays most attention to the idea of "iterative development" to reduce high frequency Probability of PCB board error.

1. High-frequency PCB board packaging drawing (confirm whether the pins in the schematic diagram are wrong);

2. After confirming the package size of the high-frequency PCB board one by one, add the verification label and add it to the package library of this design;

3. Check the schematic diagram, pay special attention to the power supply and ground of the device (the power supply and ground are the blood of the system, and there should be no negligence);

4. Manual wiring (check the power ground network while cloth, as mentioned before: the power network uses copper laying method, so use less wiring);

5. Import the netlist, adjust the signal sequence in the schematic diagram while layout (OrCAD component automatic numbering function can no longer be used after layout);

In a word, the guiding ideology in the design of high-frequency PCB board is to draw the package layout and correct the schematic diagram at the same time (considering the correctness of signal connection and the convenience of signal routing).

7. The crystal oscillator should be as close as possible to the chip, and there should be no wiring under the crystal oscillator, and the network copper skin should be laid. Clocks used in many places are wired in a tree-shaped clock tree.

8. The arrangement of the signals on the connector has a great influence on the difficulty of wiring, so it is necessary to adjust the signals on the schematic while wiring (but do not renumber the components).

9. Design of multi-board connector:

1. Straight socket: the upper and lower interfaces are mirrored and symmetrical;

2. Use flat cable connection: the upper and lower interfaces are the same.

10. Design of module connection signal:

1. If the two modules are placed on different sides of the high-frequency PCB board, then the serial number of the control system should be connected to the small and large;

2. If two modules are placed on the same side of the high-frequency PCB board, then the serial number of the control system will be connected to the small one (mirror connection signal).

Doing so can place the signal to cross as in the right image above. Of course, the above method is not a rule. I always say that everything changes as needed (this can only be understood by yourself), but in many cases, designing in this way is very useful.

11. Design of power ground loop:

The power and ground wires are routed close to each other, reducing the loop area and electromagnetic interference (679/12.8, about 54 times). Therefore, the power and ground should be as close as possible to the trace! And the signal line should be avoided as much as possible to run the line to reduce the mutual inductance effect between the signals