PCB Circuit Board Design Process Description

The design of printed circuit board is based on the circuit schematic diagram to realize the functions required by the circuit designer. Printed circuit board design mainly refers to layout design, which needs to consider various factors such as the layout of external connections, the optimized layout of internal electronic components, the optimized layout of metal connecting wires and through holes, electromagnetic protection, and heat dissipation. Excellent layout design can save production cost and achieve good circuit performance and heat dissipation performance. Simple layout design can be realized manually, while complex layout design needs to be realized with the help of computer-aided design (CAD).

Ground Design

In electronic equipment, circuit boards, circuit boards, PCB boards, grounding is an important method of controlling interference. If grounding and shielding can be used correctly in combination, most interference problems can be solved. Electronic equipment in the ground structure is roughly the system ground, chassis ground (shielding ground), digital ground (logic ground) and simulation ground and so on. In the ground design should pay attention to the following points:

a, The Correct Choice of Single-point Grounding and Multi-point Grounding

Low-frequency circuits, the signal operating frequency is less than 1MHz, its wiring and the inductance between the device has less impact, and the grounding circuit to form a loop current on the interference has a greater impact, and thus should be used a point of grounding. When the signal operating frequency is greater than 10MHz, the ground impedance becomes very large, at this time should try to reduce the ground impedance, should be used in close proximity to the multi-point grounding. When the operating frequency of 1 to 10MHz, if a point of grounding, the length of the ground line should not exceed 1/20 of the wavelength, otherwise it should be used multi-point grounding method.

b, Separate Digital Circuits and Simulation Circuits

Circuit boards have both high-speed logic circuits and linear circuits, they should be separated as far as possible, and the ground of the two do not mix, respectively, with the power supply terminal ground connected. To maximize the grounding area of the linear circuit.

c, Try to Thicken the Ground Wire

If the ground wire is very thin, the ground potential changes with the current changes, resulting in electronic equipment, timing signal level instability, anti-noise performance deterioration. Therefore, the ground wire should be as thick as possible, so that it can pass three times the permissible current of the printed circuit board. If possible, the width of the grounding wire should be greater than 3mm.

d, The Grounding Line Will Constitute a Dead Loop Circuit

When designing a printed circuit board ground system consisting only of digital circuits, making the ground line a dead loop can significantly improve noise immunity. The reason is: the printed circuit board has a lot of integrated circuit components, especially in the case of power-consuming components, due to the limitations of the thickness of the ground wire, will produce a large potential difference in the ground junction, resulting in a decline in the ability to resist noise, if the structure of the ground into a loop, will reduce the value of the potential difference, improve the noise immunity of electronic equipment.

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