After defining the properties of the difference pairs, the two difference pairs can be routed together to ensure the difference in line width, distance and length. When encountering obstacles, the two difference pairs can be separated automatically, and the mode of passing holes can be selected when changing layers.
1. On a 12-layer PCb board, there are three power supply layers of 2.2v, 3.3v and 5v. The three power supplies are placed in one layer respectively.
Generally speaking, the three power sources are done in three layers, which is better for signal quality. Because it is unlikely that the signal will be divided across plane layers. Cross-segmentation is a key factor affecting signal quality, but it is generally ignored by simulation software. For both the power layer and the formation, it is equivalent to the high frequency signal. In the real world, in addition to considering signal quality, power source plane coupling (using adjacent ground planes to reduce AC impedance of the power plane) and layered symmetry are all factors to be considered.
2. How to check whether the PCB meets the design process requirements when leaving the factory?
Many PCB manufacturers have to go through the network connection test of power-on before PCB processing is completed, to ensure that all the connections are correct. At the same time, more and more manufacturers are also using X-ray tests to check for some faults in etching or laminating. For the finished board after patch processing, ICT test and inspection are generally adopted, which requires adding ICT test points during PCB design. If something goes wrong, a special X-ray inspection device can be used to determine whether the fault is caused by processing.
3, "the protection of the mechanism" is not the protection of the case?
Yes. The casing should be as tight as possible, with little or no conductive materials, and grounded as far as possible.
4, when choosing the chip, whether also need to consider the esd problem of the chip itself?
Whether double or multi - layer board, should try to increase the area. In the selection of chips to consider the ESD characteristics of the chip itself, these are generally mentioned in the chip instructions, and even different manufacturers of the same kind of chip performance will vary. Pay more attention to the design, consider a comprehensive point, the performance of the circuit board will be guaranteed. However, ESD problems may still occur, so the protection of the mechanism is also very important for ESD protection.
5. When making pcb board, in order to reduce interference, should the ground wire form a closed sum?
When doing PCB board, generally speaking, to reduce the loop area, in order to reduce interference, when the ground wire, should not be cloth into a closed form, but cloth into dendritic better, there is to increase the area as much as possible.
6. If the simulator uses one power source and the pcb board uses one power source, should the two power sources be connected together?
If you can use a separate power supply is of course better, because it is less likely to cause interference between power sources, but most equipment has specific requirements. Since the simulator and PCB board use two power supplies, in my opinion, should not be shared.
7. A circuit consists of several pcb boards. Should they share the ground?
A circuit consists of several PCBS, most of which require common ground, because it is not practical to use several power supplies in a circuit after all. But if you have specific conditions, you can use different power sources with less interference of course.
8. Design a hand-held product with LCD and metal shell. When testing ESD, cannot pass the ICE-1000-4-2 test, CONTACT can only pass 1100V, AIR can pass 6000V. During ESD coupling test, you can only pass 3000V horizontally and 4000V vertically. The main frequency of the CPU is 33MHZ. Is there any way to pass ESD testing?
Handheld products are metal shell, ESD problems must be more obvious, LCD is afraid there will be more adverse phenomena. If there is no way to change the existing metal material, it is suggested to add electric proof material inside the mechanism, strengthen the PCB ground, and find a way to ground the LCD. Of course, how to do it depends on the circumstances.
9, design a system containing DSP, PLD, from which aspects to consider ESD?
In terms of the general system, the main consideration should be given to the part of the human body directly in contact with the circuit and the mechanism for appropriate protection. How much impact ESD will have on the system depends on the situation. Dry environment, ESD phenomenon will be more serious, more sensitive and fine system, ESD impact will be relatively obvious. Although ESD effects are sometimes not obvious in large systems, it is important to design them with care to prevent them from happening.