Advises for high-frequency PCB circuit design

2017/3/7 14:21:52

Advises for high-frequency PCB circuit design  

1. In the system of digital and analog coexistence, there are two kinds of processing methods.One is to separate digital and analog, on the grounding layer, the digital ground and analog ground are independent with a single-point connection by copper or FB magnetic bead, and the power is not separated; the other is that analog power and digital is separately powered with FB connection, but uniformly grounded. Do the two methods have the same effect?

The principle is the same. Because the power supply and ground are equivalent to the high frequency signal. The purpose of distinguishing the analog and digital part is for anti-interference mainly from digital circuit on the analog circuit. However, segmentation may cause the signal return path to be incomplete, affecting the signal quality of the digital signal and the EMC quality of the system. Therefore, regardless of which plane to split, you should notice whether the signal return path is increased, and how much interference of the return signal on the normal working signal is. Now there are some mixed designs, regardless of power and ground in layout, separately doing layout and routing according to the digital and analog part, to avoid cross-district signal.

2. Security issues: What is the specific meaning of FCC and EMC?

FCC: Communications Commission

EMC: electromagnetic compatibility

FCC is a standard organization, and EMC is a standard. The standard promulgation has the corresponding reason, standard and test method.

3. What is the differential line?

Differential signal refers to using two signals exactly the same, but of opposite polarity to transmit all the way, relying level difference of two signals to judge. In order to ensure that the two signals are exactly the same, keeping parallel in the wiring, and the line width and line spacing remains unchanged.

4. PCB simulation software:

There are many types, and commonly used software for integrity analysis and simulation analysis (SI) in high-speed digital circuit signal include icx, signalvision, hyperlynx, XTK and speectraquest, etc.

5. How does PCB simulation software carry out LAYOUT simulation?

In high-speed digital circuits, in order to improve the signal quality and reduce the difficulty of wiring, multi-layer board and specialized power layer are frequently used.

6. In the layout and wiring, how to achieve the stability of more than 50M signal?

The key to high-speed digital signal routing is to reduce the impact of transmission lines on signal quality.Therefore, the high-speed signal layout of more than 100M requires signal traces as short as possible. In digital circuits, high-speed signals are defined by the signal rise delay time.Moreover, the method of ensuring the signal quality is not the same for different types of signals (such as TTL, GTL, LVTTL).

7. The radio frequency and intermediate-frequency part of outdoor unit, and even the low-frequency circuit part for monitoring outdoor unit are often applied in the same PCB.I wonder if there are any requirements on the PCB material. How to prevent radio frequency, interference between intermediate frequency and low frequency circuit?

Hybrid circuit design is a big problem and difficult to have a perfect solution. General RF circuit in the system is regarded as a separate board for layout and wiring, and even has a special shield cavity. And the RF circuit is generally single or double-sided and relatively simple, all of which are to reduce the RF circuit distribution parameters and improve the consistency of the RF system.Compared with the general FR4 material, RF circuit board tends to the substrate of high Q value, whose material has the relatively small dielectric constant, small distribution capacitance of the transmission line, high impedance and small delay of signal transmission.In the hybrid circuit design, although the RF and digital circuits are on the same PCB, but generally RF circuit area and digital circuit area are divided for respective layout and wiring.

8. What solution does mentor have when RF,intermediate-frequency and low-frequency parts are on the same PCB?

Mentor's board-level system design software, in addition to the basic circuit design function, there are specialized RF design module.In the RF schematic design module, it provides parametric device model and bi-directional interface with EESOFT and other RF circuit analysis and simulation tools. In the RF LAYOUT module, it provides a pattern editing function for RF circuit layout and wiring, and also a bi-directional interface with EESOFT and other RF circuit analysis and simulation tools. The results of analysis and simulation can be back to the schematic and PCB.At the same time, through design management functions of Mentor, you can easily achieve design reuse, derived and collaborative design, greatly speeding up the hybrid circuit design process. The handset board is a typical hybrid circuit design, and many large cell phone design manufacturers are using Mentor and eesoft as design platforms.

9. Mentor's product structure

Mentor Graphics PCB tools are WG (original veribest) series and Enterprise (boardstation) series.

10. Mentor’s PCB design software supports BGA, PGA, COB and other packaging, how does it realize this?

Mentor's autoactive RE developed by the acquisition of veribest, is the industry's first grid-less and any angle wiring device. As we all know, for the ball grid array, COB device, grid-less and any angle wiring are the key to solve the cloth rate. In the latest autoactive RE, the new addition of push through the hole, copper foil, REROUTE and other functions, making it more convenient to use. In addition, it supports high-speed routing, including delay requirements for signal routing and differential pair routing.

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