Must have knowledge of PCB
1. If the circuit system designed contains FPGA devices, Quartus II software is required to verify the pin assignment before drawing the schematic.Some special pins in the FPGA cannot be used as normal IO.
2. From top to bottom, the 4 layers are: signal plane layer, ground, power supply and signal plane layer;The 6 layers, from top to bottom, are: signal plane layer, ground, signal inner electric layer, signal inner electric layer, power supply and signal plane layer.6 layers above the plate (advantage is: anti-interference radiation), select the inner electric layer to go through the line first, do not go through the plane layer, and do not go through the line from the ground or the power layer (cause: it will divide the power layer, resulting in parasitic effect).
3. Wiring of multi-power system: for example, FPGA+DSP system makes 6 layers, generally at least 3.3v + 1.2v + 1.8v +5V.
3.3v is usually the main power supply, which is directly laid on the power supply layer and easily connected to the global power network through the hole.
The 5V is usually a power input and requires only a small area to be covered with copper.And be as thick as possible.
1.2v and 1.8v are kernel power sources (if connected directly, it will be very difficult to be faced with BGA devices). When laying out, try to separate 1.2v from 1.8v and arrange the connected components within 1.2v or 1.8v in a compact area and connect them by copper
All in all, since the power network is spread over the entire PCB, it will be very complicated and will be far around if the wireway is adopted, and using the copper-clad method is a good choice!
4. The routing between adjacent layers adopts the crossing method: it can not only reduce the electromagnetic interference between parallel wires, but also facilitate the routing.
5. Analog digital should be isolated.The layout of the device used for analog signals will be separated from digital signals, and then cut from the AD chip!
Analog signal spread on analog ground, analog ground/analog power supply and digital power supply are connected via inductance/magnetic bead single point.
6. PCB design based on PCB design software can also be seen as a software development process. Software engineering pays most attention to the idea of “iterative development” and reduces 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 vessels of the system, which cannot be neglected at all);
(2) PCB packaging drawing (confirm whether the pin in the schematic diagram is wrong);
(3) after the PCB package size is confirmed one by one, the validation label is added to the design package library;
(4) import the network table, adjust the signal sequence in the schematic diagram while laying out the layout (the component automatic number function of OrCAD cannot be used after laying out);
(5) manual wiring (check the power ground network at the side of cloth. As mentioned above, the power network USES the copper-laying mode, so it USES less routing);
In conclusion, the guiding idea in PCB design is to draw the schematic diagram of the feedback correction at the side of packaging layout (considering the correctness of signal connection and the convenience of signal routing).
7. The crystal oscillator is as close to the chip as possible, and under the crystal oscillator it is as close to the wire as possible, and the ground network copper.Clocks 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 the signals on the schematic diagram should be adjusted along the wiring (but the components should not be numbered again).
9. Design of multi-board connector:
(1) use linear connection: the upper and lower interfaces are the same;
(2) straight socket: the upper and lower interfaces are symmetrical
10. Module connection signal design:
(1) if the two modules are placed on the same side of the PCB, discipline the serial number big connect small connect big (mirror connection signal);
(2) if the two modules are placed on different sides of the PCB, the sequence number is small and large.
This will place the signal across like the upper right.Of course, the above method is not a rule, I always say, things change on demand (this can only be understood by itself), but in many cases it works.
knowledge of PCB
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