PCB News - Common sense of high frequency PCB wiring (6)

Common sense of high frequency PCB wiring (6)

PCB factory: 1. In a system where digital and imitation coexist, there are two ways to deal with it. One is to separate the digital ground from the imitation ground. For example, in the stratum, the digital ground is a separate piece, the imitation ground is a separate piece, and the single point uses copper. Or FB magnetic beads are connected, but the power supply is not separated; the other is to imitate the separation of the power supply and the digital power supply with the FB connection, and the ground is uniformly grounded.

It should be said that it is the same in principle. Because power and ground are equivalent to high-frequency signals.

The purpose of distinguishing the imitation and the digital part is for anti-interference, mainly the interference of the digital circuit to the imitating circuit. However, cutting may result in an incomplete signal return path, affecting the signal quality of the digital signal, and affecting the EMC quality of the system.

Therefore, no matter which plane is cut, it depends on whether this is done, whether the signal return path is increased, and how much the return signal interferes with the normal operation signal. There are also some mixed plans, regardless of power supply and ground, in the layout, according to the digital part, imitating the part of the layout and wiring, to prevent the appearance of cross-zone signals.

2. Safety issues: What is the detailed meaning of FCC and EMC?

FCC: federal communication commission
EMC: electro megnetic compatibility
FCC is a normative arrangement, and EMC is a norm. There are corresponding reasons, norms and test methods for the specification announcement.
3. What is differential wiring?
Differential signals, some of which are also called differential signals, use two completely the same signals with opposite polarities to transmit one data, and the judgment depends on the level difference of the two signals. In order to ensure that the two signals are completely consistent, they must be parallel when wiring, and the line width and line distance must be unchanged.
4. What are the PCB simulation software?
There are many types of simulations, and the software for high-speed digital circuit signal integrity analysis and simulation analysis (SI) are icx, signalvision, hyperlynx, XTK, speectraquest and so on. Some also use Hspice.
5. How does PCB simulation software perform LAYOUT simulation?
In high-speed digital circuits, in order to improve signal quality and reduce the difficulty of wiring, multi-layer boards are generally used to allocate special power layers and ground layers.
6. How to deal with the layout and wiring to ensure the stability of signals above 50M
The key to high-speed digital signal wiring is to reduce the impact of transmission lines on signal quality. Therefore, the layout of high-speed signals above 100M requires the signal traces to be as short as possible. In digital circuits, high-speed signals are defined by the time the signal rises and delays. Moreover, different types of signals (such as TTL, GTL, LVTTL) have different ways to ensure signal quality.
7. The radio frequency part, intermediate frequency part, and even the low frequency circuit part that monitors the outdoor unit are often arranged on the same PCB. What are the raw material requirements for such a PCB? How to prevent interference between radio frequency, intermediate frequency and even low frequency circuits?
Hybrid circuit planning is a big problem. It is difficult to have a perfect solution. Generally, the radio frequency circuit is arranged and wired as an independent single board in the system, and even has a special shielding cavity. Moreover, the radio frequency circuit is generally single-sided or double-sided, and the circuit is relatively simple. All of these are to reduce the impact on the spreading parameters of the radio frequency circuit, and to improve the consistency of the radio frequency system is related to the general FR4 raw materials. The tendency of the radio frequency circuit board and the selection of high Q The value of the base material, the dielectric constant of this material is relatively small, the transmission line dispersion capacitance is small, the impedance is high, and the signal transmission delay is small. In hybrid circuit planning, although the radio frequency and digital circuits are built on the same PCB, the radio frequency circuit area and the digital circuit area are generally divided into separate layout and wiring. Use grounding via tape and shielding box to shield between them.
8. Regarding the radio frequency part, the intermediate frequency part and the low frequency circuit part are scattered on the same PCB. What solutions does mentor have?
Mentor's board-level system planning software, in addition to the basic circuit planning functions, also has a dedicated RF planning module. In the RF schematic planning module, parametric equipment models are provided, and two-way interfaces with EESOFT and other radio frequency circuit analysis simulation tools are provided; in the RF LAYOUT module, it provides graphic modification functions dedicated to the layout and routing of radio frequency circuits. The bidirectional interface of EESOFT and other radio frequency circuit analysis simulation tools, and the results of the analysis simulation can be back-annotated back to the schematic and PCB.
Together, using the planning management function of Mentor software can facilitate planning reuse, planning derivation, and collaborative planning. Greatly speed up the process of hybrid circuit planning. The mobile phone board is a typical hybrid circuit plan, and many large mobile phone planners use Mentor and Angelen's eesoft as the planning channel.
9. What is the product structure of Mentor?
Mentor Graphics' PCB tools include WG (formerly veribest) series and Enterprise (boardstation) series.
10. How does Mentor's PCB planning software support BGA, PGA, COB and other packages?
Mentor's autoactive RE is developed from the acquired veribest and is the industry's first gridless, arbitrary viewpoint router. As we all know, with regard to ball grid arrays, COB equipment, gridless, and arbitrary viewpoint routers are the key to solving the distribution rate. In the latest autoactive RE, new functions such as push vias, copper foil, and REROUTE have been added to make its application more convenient. In addition, he supports high-speed wiring, including delay-required signal wiring and differential pair wiring.
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