The design of printed circuit boards is based on circuit schematics to fulfill the functions required by circuit designers. The design of printed circuit boards mainly refers to map design, which requires consideration of various factors such as the layout of external connections, optimized layout of internal electronic components, optimized layout of metal connections and vias, electromagnetic protection, and heat dissipation. Excellent map design can save production costs and achieve good circuit and heat dissipation functions. Simple map design can be completed with craftsmanship, while complex map design requirements can be accomplished with the help of computer-aided design (CAD).

1. Ground wire design

Grounding is an important method for controlling disturbances on circuit boards, circuit boards, and PCB boards in electronic devices. If grounding and shielding can be combined correctly, most disturbance problems can be solved. The grounding structure in electronic devices generally includes system grounding, chassis grounding (shielding grounding), digital grounding (logical grounding), and simulation grounding. In the design of ground wires, the following points should be noted:

1) Correctly select single point grounding and multi-point grounding

In low-frequency circuits, the operating frequency of the signal is less than 1MHz, and the influence of inductance between its wiring and equipment is relatively small. However, the circulating current formed by the grounding circuit has a greater impact on disturbance, so a point grounding should be selected. When the signal operation frequency is greater than 10MHz, the ground impedance becomes very large. At this time, the ground impedance should be reduced as much as possible and multiple grounding points should be selected nearby. When the homework frequency is between 1-10MHz, if a single grounding point is selected, the length of the ground wire should not exceed 1/20 of the wavelength. Otherwise, the multi-point grounding method should be used.

2) Separate digital circuits from analog circuits

There are both high-speed logic circuits and linear circuits on the circuit board, so they should be separated as much as possible, and the ground wires of the two should not be mixed and connected separately to the ground wire of the power supply end. Try to increase the grounding area of linear circuits as much as possible.

3) Try to thicken the grounding wire as much as possible

If the grounding wire is very thin, the grounding potential will change with the change of current, causing the timing signal level of electronic devices to be unstable and the anti noise function to deteriorate. Therefore, the grounding wire should be thickened as much as possible so that it can pass three times the allowable current of the printed circuit board. If possible, the width of the grounding wire should be greater than 3mm.

4) Form a dead loop with the grounding wire

When designing the grounding system of a printed circuit board consisting only of digital circuits, making the grounding wire a dead loop can significantly improve its noise resistance. The reason is that there are many integrated circuit components on the printed circuit board, especially when encountering components with high power consumption. Due to the constraints of the thickness of the grounding wire, a large potential difference will occur at the ground junction, causing noise resistance to decrease. If the grounding structure is formed into a loop, the potential difference will be reduced, improving the noise resistance of electronic devices.

Article source: PCB manufacturerhttp://www.yonghongpcb.com/