1. If the designed circuit system contains FPGA devices, the pin assignment must be verified by Quartus II software before drawing the schematic diagram. (some special pins in FPGA cannot be used as ordinary IO).

2. From top to bottom, the 4-layer boards are: signal plane layer, ground, power supply and signal plane layer; From top to bottom, the 6-layer boards are: signal plane layer, ground, signal internal electric layer, signal internal electric layer, power supply and signal plane layer. For the board with more than 6 floors (the advantage is: anti-interference radiation), the wiring of the internal electric layer is preferred. If it cannot go through the plane layer, the wiring from the ground or the power layer is prohibited (reason: it will divide the power layer and produce parasitic effect).

3. Wiring of multi power supply system: if FPGA + DSP system is made of 6-layer board, it will generally have at least 3.3V + 1.2V + 1.8V + 5V.

3.3V is generally the main power supply. The power layer is directly laid, and the global power network can be easily set up through vias;

5V may generally be the power input, and only copper needs to be laid in a small area. And as thick as possible.

1.2V and 1.8V are core power supplies (it will be very difficult to face BGA devices if they are directly connected by wire). During layout, 1.2V and 1.8V shall be separated as far as possible, and the components connected within 1.2V or 1.8V shall be arranged in a compact area and connected by copper sheet, as shown in the figure:

In short, because the power network is all over the whole PCB, if the wiring method is adopted, it will be very complex and will go far. The method of laying copper sheet is a good choice!

4. The routing between adjacent layers adopts cross mode: it can not only reduce the electromagnetic interference between parallel conductors, but also facilitate routing.

5. Analog to digital isolation, how isolation method? During layout, the devices for analog signals are separated from those for digital signals, and then cut across the ad chip!

The analog signal is laid on the analog ground, and the analog ground / analog power supply is connected with the digital power supply through a single point of inductance / magnetic bead.

6. PCB design based on PCB design software can also be regarded as a software development process. Software engineering pays most attention to the idea of "iterative development" to reduce the probability of PCB errors.

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

(2) PCB package drawing (confirm whether the pins in the schematic diagram are wrong);

(3) After confirming the PCB package size one by one, add the verification label to the design package library;

(4) Import the net list and adjust the signal sequence in the schematic diagram while layout (the automatic component numbering function of OrCAD can no longer be used after layout);

(5) Manual wiring (check the power supply and ground network while laying, as mentioned earlier: the power network uses copper laying, so wiring is less used);

In short, the guiding ideology in PCB design is to feed back and correct the schematic diagram while drawing packaging layout and wiring (considering the correctness of signal connection and the convenience of signal wiring).

7. The crystal oscillator shall be as close to the chip as possible, and the wire shall not be laid under the crystal oscillator as far as possible, and the network copper sheet shall be paved. The clocks used in multiple places are wired in a tree clock tree.

8. The arrangement of signals on the connector has a great impact on the difficulty of wiring, so it is necessary to adjust the signals on the schematic diagram while wiring (but never re number the components).

9. Design of multi board connector:

(1) Use flat cable connection: the upper and lower interfaces are consistent;

(2) Straight socket: the upper and lower interfaces are mirrored symmetrically, as shown in the following figure:

10. Design of module connection signal:

(1) If the two modules are placed on the same side of the PCB, the discipline serial number is larger than the smaller (mirror connection signal);

(2) If the two modules are placed on different sides of the PCB, the discipline serial number is small and large.

In this way, the signals can be placed to cross like the right figure above. Of course, the above method is not a rule. I always say that everything changes as needed (this can only be understood by myself), but it works well in many cases.

11. Design of power ground circuit:

The power ground circuit in the figure above has a large area and is vulnerable to electromagnetic interference.

Through improvement in the above figure - the power supply and ground wire are close to the wiring, the loop area is reduced and the electromagnetic interference is reduced (679 / 12.8, about 54 times). Therefore, the power supply and ground should be as close to the wiring as possible! The parallel routing between signal lines should be avoided as far as possible to reduce the mutual inductance effect between signals.