Code for layout design of science and technology expansion PCB
ClassifICation by parts
Content of technical specification
1. PCB wiring and layout
PCB wiring and layout isolation standards: strong and weak current isolation, large and SMAll voltage isolation, high and low frequency isolation, input and output isolation, digital and analog isolation, input and output isolation. The dividing standard is an order of magnitude difference. Isolation methods include keeping away from space and grounding.
2. PCB wiring and layout
The crystal oscillator should be as close to the integrated circuit as possible, and the wiring should be thicker
3. PCB wiring and layout
Crystal case grounding
4. PCB wiring and layout
When the clock line outputs through the connector, the pins on the connector should be covered with grounding pins around the clock line pins
5. PCB wiring and layout
Analog and digital circuits are allowed to have their own power and ground paths. If possible, expand the power supply and grounding of these two parts of the circuit, or use separate power supply and grounding layer to reduce the power supply and grounding. Impedance of conductor circuit to reduce any interference voltage that may exist in power supply and grounding circuit
6. PCB wiring and layout
Circuit board

The analog ground and digital ground of the PCB working independently can be connected to a single point near the system grounding point. If the power supply voltage is the same, the power supply of analog and digital circuits is connected at a point at the power inlet. If the supply voltages are different, the two supplies are closer. Place a 1~2nf capacitor to provide a path for the signal return current between the two power supplies
7PCB wiring and layout
If the PCB is inserted into the main board, the power and grounding of the analog and digital circuits of the main board should also be separated. Analog and digital grounding are grounded at the main board grounding point, and the power supply is connected at a single point near the system grounding point. If the power supply voltage is the same, the power supply of analog circuit and digital circuit is connected at a point at the power inlet. If the power supply voltage is inconsistent, a 1~2nf capacitor is combined near the two power supplies to provide a path for the signal return current between the two power supplies.
8. PCB wiring and layout
When high-speed, medium speed and low-speed digital circuits are mixed, different layout areas shall be allocated on the printed board
9PCB wiring and layout
Separate low-level analog circuits and digital logic circuits as much as possible
10PCB wiring and layout
When designing multilayer printed boards, power boards should be close to the ground plane and arranged below the ground plane.
11PCB wiring and layout
When designing a multilayer PCB, the wiring layer should be arranged adjacent to the entire metal plane
12PCB wiring and layout
In the design process of multilayer printed boards, digital circuits and analog circuits are separated, and where possible, digital circuits and analog circuits are arranged in different layers. If it must be arranged on the same layer, trenching, grounding wire and isolation can be used to correct this situation. Analog and digital grounding and power supply must be separated and cannot be mixed
13 PCB wiring and layout
Clock circuit and high-frequency circuit are the main sources of interference and radiation. They must be arranged separately from sensitive circuits.
14 PCB wiring and layout
Pay attention to waveform distortion during long line transmission
15PCB wiring and layout
The best way to reduce the loop area of interference sources and sensitive circuits is to use twisted pairs and mask wires to wind the signal wire and ground wire (or current carrying circuit) together, so that the distance between the signal and ground wire (or current carrying circuit) is the nearest

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