1, if the design of the circuit system contains the FPGA device, it is necessary to use the II Quartus software to verify the distribution of the pin before drawing schematic diagram. (some of the special pins in the FPGA can't be used as ordinary IO).
2, 4 layers from top to down is as follows: the signal level, power supply, signal plane layer; 6 layers from top to bottom as follows: signal level, signal in electric layer, signal electric layer, a power supply, a signal plane layer. 6 layers or above board (the advantage is: anti interference radiation), the priority choice of the electric layer to walk the line, can not open the choice of planar layer, prohibit from the ground or power source line (reason: will split the power layer, produce parasitic effect).
3, multi power system wiring: such as the FPGA+DSP system to do 6 laminates, there will be at least 3.3V+1.2V+1.8V+5V.
3.3V is the main power supply layer is spread directly through the hole, it is easy to succeed in the global power supply network;
5V is generally the power input, only need to shop in a small area of copper. And as far as possible (you ask me how thick - can be more rough, the thicker the better);
1.2V and 1.8V is separated from the kernel power (if the line is connected with the way will encounter great difficulties in the face of BGA), layout as 1.2V and 1.8V, and let 1.2V and 1.8V connected component placement in a compact area, the use of copper skin connection
In short, because the power network throughout the entire PCB, if the use of the way the line will be very complex and will be around a long way, the use of copper clad method is a good choice!
4, the adjacent layer between the line using the cross way: it can reduce the electromagnetic interference between parallel wires (high school Oh), and easy to walk.
5, analog digital to be isolated, how to isolate the layout of the device will be used for analog signals and digital signals of the device separately, and then from the AD chip in the middle of the!
The analog signal with analog, analog and digital / analog power supply through magnetic inductor / single point connection.
6 and PCB design based on PCB design software can also be regarded as a kind of software development process, software engineering pay most attention to the idea of iterative development, I think in PCB design can also introduce the thought and reduce the probability of error of PCB.
(1) schematic diagram, in particular, pay attention to the power of the device and the ground (power supply and the system of blood vessels, can not be the slightest negligence);
(2) PCB package drawing (to confirm whether the principle of the principle of the pin is wrong);
(3) after the PCB package size one by one to confirm, add the verification tag, added to the design of the package library;
(4) introduction to the network table, while the layout of the principle of the layout of the signal sequence (the layout can not be used after the OrCAD component automatic numbering function);
(5) manual wiring (check the power network side edge, said: power supply network using copper, so use less wire);
In short, the guiding principle of the design of PCB is to draw the schematic diagram of the layout and wiring of the package layout (from the correctness of the signal connection, the convenience of the signal line).
7, try to close the crystal crystal chip, and try not to walk the line, floor network copper. Multiple use clock tree clock tree routing.
8, arrangement of the connector signal wiring difficulty degree of influence is bigger, therefore should be side wiring side adjustment schematic diagram of signal (but do not to the number of components).
9, multi board connector design:
(1) use the cable to connect on the same interface;
(2) straight socket: upper and lower mirror image symmetry,
10, module connection signal design:
(1) if the 2 modules are placed on the same side of the PCB, the number of the discipline is connected to a small number of large (mirror image connection signal);
(2) if the 2 modules on the PCB of different surfaces, then the small number of small pick up the discipline.
It can be placed above the same as signal intersection. , of course, the above methods are not rule, I always say, everything with the need, this can only comprehend their own), but in many cases according to this way of design is very useful bale.
11, the design of power supply circuit:
By improving the power supply and the ground wire near the line, reducing the loop area, reducing the electromagnetic interference (679/12.8, about 54 times). Therefore, the power supply and the ground should be close to the line, and the signal line should try to avoid parallel walk line, reduce the mutual effect between the signal.