1. If the designed circuit system contains FPGA devices, it is necessary to use Quartu ll software to verify the pin assignment before drawing the schematic diagram. (Some special pins in FPGA cannot be used as normal IO).
2. The order from top to bottom of the 4-layer board is: signal plane layer, ground, power supply, and signal plane layer: the order of the 6-layer board from top to bottom is: signal plane layer, ground, signal internal electrical layer, signal internal electrical layer, Power and signal plane layers. For boards with more than 6 layers (advantage: anti-interference radiation), the inner layer wiring is preferred, and the plane layer cannot be left. It is forbidden to route from the ground or power layer (reason: it will split the power layer and cause parasitic effects).
3. Wiring of multi-power supply system: If FPGA+DSP system is made of 6-layer board, generally there will be at least 3.3V+1.2V+1.8V+5V.
3.3V is generally the main power supply, directly laying the power supply layer, and it is easy to connect the global power supply network through vias;
5V may generally be an auxiliary power input, and only a small area of copper needs to be laid. And as thick as possible.
1.2V and 1.8V are the core power supply (if you directly use wire connection, you will encounter great difficulties in the face of BGA devices), try to separate 1.2V and 1.8V during layout, and let 1.2V or 1.8V be connected Components are arranged in a compact area and connected by copper skin.
In short, because the power network is spread all over the entire PCB, if the wiring method is used, it will be very complicated and will go around for a long distance. The method of laying copper is a good choice!
4. The wiring between adjacent layers adopts a crossover method: it can not only reduce the electromagnetic interference between parallel wires, but also facilitate wiring.
5. Analog and digital need to be isolated, what is the isolation method? When laying out, the devices used for analog signals are separated from the devices for digital signals, and then one size fits all from the middle of the AD chip!
The analog signal is laid on the 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. 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 (the power supply and ground are the blood vessels 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 the PCB package size is confirmed one by one, add a verification label and add it to the design package library;
(4) Import the netlist, and adjust the signal sequence in the schematic diagram while laying out (OrCAD's automatic component numbering function can no longer be used after layout).
