PCB Technical - High-speed PCB design and copy board simulation strategy

At present, high-speed PCB design is widely used in fields such as communications, computers, and graphics and image processing. In these fields, engineers use different high-speed PCB design strategies, which involve over-design strategies of board copy simulation and analysis.

In the field of telecommunications, the design is very complicated, and the transmission speed in data, voice and image transmission applications is far higher than 500Mbps. In the field of communications, people are pursuing faster launching of higher-performance products, but the cost is not the first. Bit. They will use more board layers, enough power planes and ground planes, and use discrete components to achieve matching on any signal lines that may have high-speed problems.

They have SI (Signal Integrity) and EMC (Electromagnetic Compatibility) experts to perform board copy simulation and analysis before wiring. Every design engineer follows strict internal design regulations. Therefore, design engineers in the communications field usually adopt this over-designed high-speed PCB design strategy.

The motherboard design in the home computer field is the other extreme. Cost and effectiveness are above all else. Designers always use the fastest, best and highest performance CPU chips, memory technology and graphics processing modules to compose increasingly complex computers. Home computer motherboards are usually 4-layer boards. Some high-speed PCB design technologies are difficult to apply to this field. Therefore, engineers in the home computer field usually use over-research methods to design high-speed PCB boards. They must fully study the specifics of the design. The situation solves those real high-speed circuit problems.

The general high-speed PCB design situation may be different. Manufacturers of key components in high-speed PCBs (CPU, DSP, FPGA, industry-specific chips, etc.) will provide relevant chip design materials, which are usually given in the form of reference designs and design guides. However, there are two problems here: First, there is also a process for device manufacturers to understand and apply signal integrity, and system design engineers always hope to use the latest high-performance chips in the first time, so the device manufacturers give design guidelines May be immature. Therefore, some device manufacturers will provide multiple versions of design guidelines at different times. Secondly, the design constraints given by the device manufacturer are usually very harsh, and it may be very difficult for the design engineer to meet all the design rules. In the absence of simulation analysis tools and no understanding of the background of these constraint rules, satisfying all constraints is the only high-speed PCB design method. Such design strategies are usually called excessive constraints.

An article mentioned that a backplane design uses surface-mounted resistors to achieve terminal matching. More than 200 such matching resistors are used on the circuit board. Imagine if you want to design 10 prototypes by changing these 200 resistors to ensure the best terminal matching effect, it will be a huge workload. In this design, none of the resistance changes benefited from the analysis results of the SI software, which is indeed surprising.

Therefore, it is necessary to add high-speed PCB design copy board simulation and analysis to the original design process to make it an indispensable part of complete product design and development.