Key points of high-speed PCB design

2019/2/21 17:20:40

The concept of high-speed PCB is only derived from a very vague comparison in the engineer's mind. Years ago, when digital circuits were just emerging, the rate was very low, and PCBs could basically work as long as they were connected. After that, the signal rate continues to increase. Slowly, when the PCB was previously painted, the old method is not working, and the PCB will have problems. The rate is coming up, the PCB is prone to problems, and this feeling is constantly strengthened, so the word high-speed PCB is born.

High-speed PCB design requires a lot of different product directions. Although some basic technologies are versatile, there are still many industry-specific technical differences, because the core design requirements of each field are different. For example, consumer products stand out for performance-price ratios; on the contrary, military and industrial fields require absolute reliability; while data and communication require extreme product performance... This is a question of design rules and technology development. Very different requirements.

high speed serial signal design

If the key points of the relatively high-speed PCB design are relatively common, I think we must pay attention to the following aspects:

1. The first is the design of the power circuit. The power supply is the basis for a stable operation of electronic products. Although the technical challenge of power supply design is not the biggest in most cases, once the problem of operational stability occurs, it is often followed by a power supply.

The main focus of the power supply design is that the power module's functional design optimization, conversion efficiency improvement, and power channel design must be carried out in accordance with the corresponding technical indicators and rules. For sensitive power supplies or large current power supplies, it is also necessary to combine PI simulation. Improves DC voltage drop and dynamic impedance as well as noise performance.

2. High-speed parallel signal design, the most common is DDR3, DDR4 and other circuits, especially for the Memory Down (on-board memory) design, more special attention, in strict implementation of the original Layout Guide, it is best to pass Simulation analysis is used to assist in optimizing the layout design to ensure high-speed signal design quality.

There are many other types of parallel signal design. Generally, the absolute length and relative length are controlled according to the corresponding chip design rules. At the same time, the rule control of the number of vias, signal cross-segmentation and crosstalk can be satisfied, and most of the designs can be satisfied. Claim.

3. High-speed serial signal design. In recent years, high-speed serial signals have developed very rapidly. Many traditional parallel bus interfaces are gradually being replaced by serial buses. For example, the most typical IDE parallel hard disk data interface is serialized by SATA. Replaced by the data interface, I believe that the application of high-speed serial signals will become more and more extensive in the future.

pcb design

At present, the most common PCIE high-speed channel, as well as SATA, SAS, LVDS, USB3.0 high-speed channel, and high-speed optical network channel, the signal speed has generally been upgraded to 5G, 8G, 10G, 28G or even 56Gbps, so it must be strict Design according to the corresponding high-speed design rules, and at the same time do signal integrity analysis and optimization work, otherwise it will be prone to signal quality problems.

4. There are many other key technical points that need attention, such as analog signal design, RF signal, digital-to-analog mixing, and design considerations for DFM, DFA, EMC, etc. Each direction has a series of rules and requirements. Interested friends can do in-depth study and study, and will not expand here.

As for the ins and outs of high-speed design, this is hard to say in a few words. Because any professional field has its own set of workflow and rules system, this is a very complicated system engineering of technology and management. If you want to have a deep understanding of an industry, you can only really understand it if you enter the industry yourself and climb for a few years.
And even in the same industry, but in different technical areas, there is also a big difference.

As the saying goes, interlacing is like a mountain. Even if you have worked in a specific field of the same industry for many years, if you switch to another field, your previous work experience may be completely cleared. For example, from the low-end consumer product design field to the military and communication product design field, the previous work experience can be very limited, because the design rules are completely different from the knowledge system. This is actually the difference between the industry and the circle, so it is not just the choice of the industry. It is more important to pay attention to the difference and choice of the circle.

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