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Although expensive for the "e-mother", in the past the country's emphasis on PCB circuit board industry, technological innovation is far less than developed countries, but fortunately the situation has now greatly improved. August 30 this year in the Shenzhen Convention & Exhibition Center CS Show 2016 as a platform to showcase professional PCB technology products and solutions, with a focus on the professional exhibition concept, as well as super-link on the ability of downstream industries, with more in the industry strong influence. The exhibition organizers will showcase the PCB, FPC, HDI, MPCB, IC carrier boards and other circuit boards, will once again fill the professional circuit board show no gaps. PCB circuit board layout has been tested PCB engineer a major problem, which RF circuit board design is more difficult, and today we take some of the sharing of experience in the design RF circuits.
The rapid development of radio frequency integrated circuits for the wireless communications in all types of engineering and technical personnel to provide a broad prospect. If the ground RF circuit mishandled, it may have some strange phenomenon. For the design of digital circuits, even if there is no ground plane, most of the digital circuit function also performed well. In the RF band, even a very short ground will be the same effect as an inductor. Roughly, for every millimeter length of the inductor is about l nH, 433 MHz when 10 to PCB circuit inductance of about 27Ω. If you do not use the ground floor, most of the ground will be longer, the circuit will not have design features. From this difficult RF circuit design.
FAQ RF circuit design
1. interference between digital and analog circuit module circuit module
If the analog circuitry (RF) and digital circuits work alone, each might work well. However, once the two on the same board, using the same power to work together, the whole system is likely to be unstable. This is mainly because the digital signal frequently between the ground and the positive supply ( "3 V) swing, and the cycle is very short, often nanosecond. Due to the large amplitude and shorter switching time. The digital signal contains a large number of such independent switching frequency and high-frequency component. In the simulation part, from a radio tuned circuit device transmitted wireless signal receiving portion is generally less than lμV. Thus the difference between the digital signal and the RF signal will reach 120 dB. Obviously, if you can not make the digital signal and RF signal well separated. Weak RF signal may be damaged, so that the wireless device performance will deteriorate, or even fail completely.
2. The noise power supply
RF circuit for the power supply noise is quite sensitive, especially for voltage spikes and other high-frequency harmonics. The microcontroller will suddenly sucked most of the current in each internal clock cycle short, this is because the modern microcontrollers use CMOS process. Therefore, assuming a microcontroller running at lMHz internal clock frequency, this frequency will extract current from the power supply. If you do not take the appropriate power supply decoupling, will lead to the power line voltage spikes. If these voltage spikes to reach the part of the RF circuit supply pin, severe cases may lead to job failure.
The antenna radiation interference of other analog circuit section
In the PCB circuit design, board usually has other analog circuits. For example, many have analog circuit, digital converter (ADC) or a digital / analog converter (DAC). Radio frequency signal emitted by the transmitter antenna may reach the analog input of the ADC. Because any circuit lines are likely to make or receive RF signals, such as an antenna. If the ADC input process unreasonable, RF signals may self-excited in the ADC input ESD diodes. Causing ADC bias.
RF circuit design principles and programs
1.RF layout concept
RF layout design, the priority must meet the following general principles:
The high power RF amplifier (HPA) and a low noise amplifier (LNA) to isolate as much as possible open, simply put, is to make high-power RF transmitter circuits away from the low-power RF receiver circuit:
PCB board to ensure the high power region at least in one piece, it is preferable not above the vias, of course, the bigger the better copper area;
Circuit and power supply decoupling is also very important;
RF output usually takes away from the RF input;
Sensitive analog signal should be as far away from high-speed digital and RF signals.
2. physical partitions and electrical partition design principles
Design partitions can be divided into physical partitions and electrical partition. Physical partition mainly related to the layout of components, direction and shielding; electrical partitions can continue to break down the power distribution, RF alignment, and signal sensing circuit and grounding partition.
3. The physical partition principle
Component location layout principles. Component layout is the key to achieving a good RF design. The most effective technique is to first fix the components located on the RF path and adjust its direction, so as to minimize the length of the RF path, away from the input output. And separating the high-power circuits and low power circuits as far as possible.
PCB stack design principles. The most effective method is to stack the board main ground plane (main land) arranged in the second layer of the subsurface, and as far as possible the RF line arranged on the surface. The through-hole size to minimize the RF path, which can not only reduce the path inductance, but also can reduce the main floor of the Weld point, and reduce the leakage of RF energy to the opportunities in other areas within the stacked plates.
RF devices and RF cabling layout principles. In the physical space, such as a multi-stage amplifier is usually sufficient to linear circuit a plurality of RF isolation between the open area, but duplexer, mixer and IF amplifier / mixer is always a plurality of RF / IF signals interfere with each other. Therefore, care must be taken to minimize this impact. RF and IF traces should be as cross, and as far as possible in the intervals between them a piece of land. The correct path of the block PCB RF performance is very important, and this is the reason most of the time component layout typically accounts in the cellular phone PCB design.
Design principles to reduce the high / low power devices coupled interference. On the cellular phone PCB, usually low-noise amplifier circuit on a side of the PCB, and the high power amplifier on the other side, and finally through the duplexer to connect them to the terminal RF and baseband processor on the same side end of the antenna. Use techniques to ensure that the through-hole will not RF energy from one side of the plate is passed to the other side, it is a common technique used in the second plane blind holes. Through the through-holes arranged in the area of PCB from RF interference are two faces to the adverse impact of the through-holes is minimized.
RF circuit design requires designers to have some practical experience and engineering design capabilities. This article summarizes some experience can help RFIC developers shorten development cycle to avoid unnecessary detours, saving manpower and resources.
As electronic components, electronic components important to support the role of PCB circuit boards in the electronics industry in the field is very important, the industry called "electron carrier." With the development of science and technology, the scope of application of the PCB will be more extensive. To some extent, the circuit board production technology has become a measure of the level of a national science and technology an important indicator. In order to better capture the world's leading PCB manufacturing technology, comprehensive display of domestic PCB industry manufacturing standards, August 30-September 1, 2016 the board of Shenzhen International Procurement Fair (CS Show 2016) in Shenzhen Convention and Exhibition Center officially kicked off the annual PCB industry sounded the horn off.