Regarding high-frequency PCB circuit design

2017/3/8 15:01:22

1. How does Mentor PCB design software deal with differential line?

After defining the property of differential pairs by Mentor software, the two differential pairs can be traced together, strictly guaranteeing the line width, spacing and length difference, and automatically separating from each other when meeting obstacles.
2. In a 12-layer PCB board, there are three power supply layer: 2.2v, 3.3v and 5v, how to deal with the ground wire if three power supplies were in one layer respectively?
In general, if three power supplies were in three layers respectively, the signal quality is better as it is unlikely appear the phenomenon of the signal across the plane. Cross-segmentation is a factor that is critical to signal quality, while simulation software generally ignores it. For the power supply and the ground layer, the high-frequency signal is equivalent. In practice, in addition to the signal quality, the power plane coupling (using the adjacent ground plane to reduce the power plane AC impedance), cascading symmetry, are the factors to be considered.
3. How to check whether PCB meets the design process requirements?
Many PCB manufacturers have to go through the network off test to ensure that all the line connection is correct when finishing PCB processing. At the same time, more and more manufacturers also use x-ray test to check some failure of etching or laminating. The finished product after the SMT processing is generally used ICT test, which requires the PCB design to add ICT test points. If a problem occurs, you can also troubleshoot by a special X-ray inspection device.
4. Is "the protection of the body" the protection ofchassis?
Yes. Thechassisshould be as tight as possible with little or no conductive material, but try to be grounded.
5. Is it necessary to consider the chip esd problem in the chip selection?
In choosing chips, you should consider the chip's own ESD characteristics, which are generally mentioned in the chip description, and even if the same chip from different manufacturers will have different performance. The performance of the circuit board has a certain guarantee if you notice this in designing.
6. In order to reduce the interference, should the ground wire constitute a closed form when manufacturing PCB board?
In general, you have to reduce the loop area to reduce the interference. As for the ground wire, it should be a dendritic shape instead of a closed form, and the area ofthe groundshould be increased as much as possible.
7. If the simulator and PCB board have a power supply respectively, should the two power supply be linked together?
It is absolutely good if using a separate power supply to for less interference, but most of the equipment has a specific requirement. Now that the simulator and PCB board are using different power supplies, there is no need to link them.
8. A circuit consists of a few PCBs, should they be common-grounded?
A circuit consists of several PCBs is mostly required common-grounded, after all it is not practical to use a few power supplies in a circuit. But if you have conditions, the interference will be smaller when using different power supplies.
9. Design a hand-held product with LCD, the shell is metal. In Testing ESD, ICE-1000-4-2 cannot pass, CONTACT only through 1100V and AIR can pass 6000V. In ESD coupling test, the level can only be through 3000V, and vertical can pass 4000V test. CPU frequency is 33MHZ. Is there any way to pass ESD tests?
ESD problem must be more obvious in handheld products and metal shell, and LCD is also likely to appear bad phenomenon. If you cannot change the existing metal material, it is recommended to add anti-electrical materials inside the organization to strengthen the grounding of PCB, and try to make the LCD ground spontaneously. Of course, the operation depends on the specific situation.
10. How to consider ESD when designing a system with DSP and PLD?
In terms of the general system, the main part of body-touching and the appropriate protection on the circuit and organization should be considered. As for the impact of ESD on the system, it will depend on different circumstances. ESD phenomenon will be more serious in dry environment, and the impact of ESD will be relatively obvious in more sensitive and sophisticated system. Although the impact of ESD on large systems sometimes is not obvious, you should pay more attention in design.
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