Today's cell phone design by various ways to integrate all things, this RF circuit board design is very negative. Now the industry is highly competitive and everybody is looking for ways to use the smallest size and the largest integrated minimum cost function. Analog, digital and RF circuits are closely packed together, used to separate space for each problem area is very small and taking into account cost factors, the circuit board layers are further minimized. Paradoxically, the multi-purpose chip, various functions can be integrated in a very small die, but also to connect the outside world was arranged between the pins and very close, so RF, IF, analog and digital signals are very close, but they usually are irrelevant in the electrical. Power distribution may be a nightmare for the designers, in order to extend battery life, different parts of the circuit is based on the needs of time-sharing work, by the software to control the conversion. This means you may need for your cell phone to provide five to six kinds of work power. in the design of RF layout,布线, there are several general principles must first be met: as much as possible the high power RF amplifier (HPA) and low-noise amplifier (LNA) to isolate, simply, is to make high-power RF transmitter away from the low power RF receiver circuit. If your PCB board has a lot of physical space, you can easily do this, but usually a lot of components, PCB space is low, thus it is usually impossible. You can place them on both sides of PCB board, or allow them to turn, rather than simultaneously. Sometimes also include high-power circuit and the voltage-controlled oscillator RF buffer (VCO). ensure the PCB, at least one high-power block area, the best is not over the top hole, of course, copper the better. Later, we will discuss how to break the design principles needed, and how to avoid problems that may arise therefrom. chip and power supply decoupling also very important, will discuss several ways to achieve this principle. RF output typically away from the RF input, we will be discussed in detail later. sensitive analog signals should be as far as possible away from the high-speed digital signals and RF signals. How to partition? design area can be divided into physical partitions and Electrical Division. Mainly related components of physical partition layout, orientation and shielding issues; Electric Division will continue to decompose for the power distribution, RF alignment sensitive circuits and signals as well as grounding the district. First we discuss the physical partition problem. Components of a good RF layout is designed to achieve critical and most effective technology is the first fixed component in the RF path and adjust its direction to the length of the RF path minimize the input from output, and as far as possible remote high-power circuit and separate low-power circuits. the most effective method of circuit board stack is the main ground plane (main land) to arrange a second layer in the subsurface, and the RF line to go as far as possible on the surface. RF path through the pore size can be reduced not only the path to minimize inductance, but also reduce the main floor of the Weld point, and reduce the RF energy leakage to other regions within layered plates opportunities. in physical space, such as multi-stage linear amplifier circuit is usually more than enough to isolate the RF zone between them, but diplexers, mixers and IF amplifier / mixer total have multiple RF / IF signal interference, so be careful to minimize this effect. RF and IF alignment should be crossed to go as far as possible, and as a piece of land in the interval between them. RF path on the right block the performance of PCB board is very important, which is why the component layout of PCB board is usually the design of cellular phones accounted for the reason most of the time. in the cell phone PCB board, usually low-noise amplifier circuit can be placed on a PCB board side, and the high power amplifier on the other side, and finally through the duplexer to connect them in the same plane to the RF side and the baseband processor side of the antenna. Need some tips to ensure that the direct RF energy through the hole will not pass from the plate side to the other side, commonly used technology is used in both sides of the blind hole. Can be arranged directly through the hole in both sides of the PCB board from RF interference through the hole area to be straight to minimize the adverse effects. times less likely among multiple circuit blocks to ensure adequate segregation, in which case we must consider the use of metal shielding to RF energy shield in the RF region, but also problems of metal shield such as: self-cost and assembly costs are expensive; irregular shape in the manufacture of metal shield difficult to ensure accuracy, rectangular or square metal shield component layout makes it subject to some restrictions; metal shield is not conducive to parts replacement and fault location; as metal shield must be welded to the ground, must maintain an appropriate distance components, it requires taking up valuable PCB board space. as possible to ensure the integrity of shielding is very important, into the metal shield of the digital signal lines should go as far as possible the inner layer, and preferably take the line layer PCB is the ground floor below. RF signal from the metal shield at the bottom of a small gap and to notch the wiring layer go out, but the gap in the surrounding fabric to be as much as possible a number of places, in different layers to be linked together through multiple vias . Despite the above problems, but the metal shield is very effective, and often the key isolation circuit is the only solution. In addition, appropriate and effective chip power supply decoupling is also very important. Many RF integrated circuit chip linear power supply is very sensitive to noise, usually every chip requires the use of up to four separate capacitor and an inductor to ensure that all of the power supply noise filter). minimum capacitance value usually depends on the self-resonant frequency and low-pin inductance, C4's value is chosen accordingly. The value of C3 and C2 pin inductance because of their own relationship to the relatively large number, so RF decoupling effect of some difference, but they are more suitable to filter out low frequency noise. Inductor L1 to the power line from the RF signal can not be coupled into the chip. Remember: all traces are both a potential to receive RF signals can also be launching antenna, while the induction of the RF signal and isolate the critical path is also necessary. The physical location of the decoupling components are usually very critical, important components of the layout of these principles are: C4 should be as close to the IC pin and ground, C3 must be closest to the C4, C2 C3 to be closest to and IC pin connection with the C4 alignment to as short as possible, these components of the ground side (especially C4) should be adopted for the next stratum is usually the ground pin is connected with the chip. Formation associated with the components should be as close as possible through-hole PCB board pad components, it is better to use to play the blind hole in the pad to minimize the cable inductance, inductance should be close to C1. an integrated circuit or amplifier often with an open drain output and requires a pullup inductor to provide a high impedance load and a low RF impedance DC power, the same principle applies to this Diangan end of the power source decoupling. Some chips require more power to 工作, so you may take two to three sets of capacitance and inductance decoupling them separately deal with, if the chip Zhouwei not have enough space, then you may experience some problems. remember very little inductance parallel close together, because it will form an air core transformer, and another induced by the interference signal, so the distance between them in which at least equivalent to the height of a device, or at right angles arranged to minimize their mutual inductance. Electrical Division and Physics Division in general the same principles, but also contains a number of other factors. Modern cell phones use different parts of the operating voltage, and using software to control it, to prolong battery life. This means that cellular phones need to run a variety of power supply, which brings more to isolate the problem. Usually from the connector into the power and immediate decoupling processing to filter out any noise from the external circuit board, and then through a switch or regulator after it distributed. cell phone most of the circuit's DC current is very small, so take the line width is usually not a problem, however, necessary for high-power amplifier as a separate take a wide line of high current to the transmission minimize pressure drop. In order to avoid too much current consumption, need to use multiple vias to the current passing from one layer to another layer. In addition, if not in high-end power amplifier power supply pin decoupling it fully, then the noise will be high-power radiation to block board, and bring a variety of problems. High power amplifier grounding are critical, and often need to design a metal shield. In most cases, the key is to ensure that the same RF output away from the RF input. This also applies to amplifiers, buffers and filters. In the worst case, if the output buffer amplifier and the appropriate phase and amplitude feedback to their input, then it is possible to generate self-excited oscillation. In the best cases, they will be able at any temperature and voltage conditions, a steady job. In fact, they may become unstable, and noise and intermodulation signal to the RF signal.If the RF signal line have input from the filter output around the back, which could seriously damage the bandpass filter characteristics. In order to get good input and output isolation, it must first filter cloth around the circle, followed by the lower filter cloth area have a piece of land around the filter with the main land link. The need to filter the signal through the line as far as possible away from the filter pin is also a good way. In addition, various parts of the grounding block board should be very careful, otherwise you may be unconsciously you do not want to introduce a coupling channel. Figure 3 details the approach the ground. sometimes chose to walk single-ended or balanced RF signal line, the cross-interference and EMC / EMI principle applies here. Balanced RF signal if alignment is correct, can reduce the noise and cross-interference, but their impedance is usually higher, but also to maintain a reasonable width to get a match signal source, take the line and load impedance, the actual wiring may there will be some difficulties. buffer can be used to increase the isolation, because it can put the same signal is divided into two parts, and used to drive a different circuit, in particular, may need to buffer the oscillator to drive the number of mixer . When the mixer in the RF frequency to reach the common mode isolation, it will not work correctly. Buffer can be well isolated in different frequencies of the impedance changes, which will not interfere with each other between the circuit. buffer on the design of great help, they can keep up in the back of the circuit needs to be driven, so take the line of high power output is very short, due to buffer the input signal level is low, so they other circuits on the board difficult to interfere. there are many very sensitive to signal and control lines require special attention, but they are beyond the scope of this paper, this paper discusses only briefly, without further detail. voltage-controlled oscillator (VCO) can be converted to changes in voltage changes the frequency, this feature is used for high-speed channel switching, but they also will control the voltage on the micro-frequency noise is converted to small change, and this increased to RF signal noise. Overall, at this level since there is no way you no longer will be noise from the RF output signal is removed. Where is it so difficult? First of all, the expectations of the line of control bandwidth may range from DC up to 2MHz, and broadband through the filter to remove the noise so it is almost impossible; Second, VCO control line is usually a control part of the frequency of the feedback loop, it many places are likely to introduce noise, so be very careful with VCO control line. to ensure the alignment of the lower RF ground is solid, and all components are firmly connected to the main floor, and noise and other possible alignment isolate. In addition, to ensure that the power has been fully VCO decoupling, as VCO's RF output is often a relatively high level, VCO output signal is easy to interfere with other circuits, the VCO must be special attention. In fact, VCO is often deployed on the end of the RF area, and sometimes it requires a metal shield. resonant circuit (one for transmitter and one for receiver) and the VCO, but it also has its own characteristics. Simply put, the resonant circuit is a diode in parallel with capacitive resonant circuit, it helps to set the VCO operating frequency and modulation of voice or data to the RF signal. all VCO design principles apply equally resonant circuit. As the resonant circuit contains quite a number of components, board and a wide distribution area usually run on a very high RF frequencies, the resonant circuit is usually very sensitive to noise. Signals are usually arranged in the chip adjacent feet, but they need to signal pin inductance and capacitance is relatively large in order to work with, which in turn requires the location of these inductors and capacitors must be in close proximity, and even back 1 pair of noise-sensitive control loop. To achieve this it is not easy. automatic gain control (AGC) amplifier is also an error-prone areas, whether there will be launched or receiving AGC amplifier circuit. AGC amplifier can effectively filter out the noise is usually, but because cellular phones equipped to handle transmit and receive signal strength rapidly changing capabilities, thus requiring AGC circuit has a very wide bandwidth, which makes some of the key circuits of the AGC amplifier is easy to the introduction of noise. AGC circuit design must follow good analog circuit design techniques, and this op amp with very short input and feedback path of the short, these two have to be away from the RF, IF, or high-speed digital signal trace. Similarly, a good grounding is also essential, and the chip power supply decoupling must be good. If you have to go in the input or output of a long-term, it is best at the output, the output impedance is usually much lower, but not easy to induced noise. Signal level is usually higher, the more easy to introduce noise into other circuits. in all PCB design, digital circuit as far as possible away from the analog circuit is a general principle, it also applies to RF PCB design. Analog to the public and for shielding and separating signal line is as important as the ground is usually the problem is if there is no predictable and careful planning in advance, every time you have done in this area are few. Therefore, in the early stages of design, careful planning, thoughtful layout of components and complete assessment of the layout is very important, because design changes caused by negligence may result in a nearly completed design must also reinvent the wheel. The result of the serious consequences of negligence, in any event on your personal career development is a good thing. lines should also be made from analog RF circuits and digital signal some very critical, all the RF alignment and component pad around the copper grounding should be filled as much as possible, and as much as possible connected with the main land . Similar to the bread plate tectonic micro-vias in the RF circuit board development phase is useful, if you choose to construct the board, then you do not need to spend any free to use a lot of overhead Jiuke through holes, or drilling in general will increase the development of PCB board cost, which will increase in the cost of mass production. line must go through if the RF signal line, then try to walk between them along the RF line of fabric layer connected to the main land. If not possible, make sure they are crossed, which can minimize the capacitive coupling, while as far as the alignment of each RF more fabric around a number of places, and to link them to the main land. In addition, the parallel RF walking distance between the lines to minimize inductive coupling can be minimized. a solid block access directly on the ground just below the first layer, the isolation was the best, although careful design is also useful when the other way. I have tried to pick a few pieces into the ground to isolate analog, digital and RF circuits, but I have never been satisfied with the results, because in the end there are always some high-speed signal lines to pass through these separate places, this is not a good. each layer in the PCB board should be cloth on the ground as much as possible, and to link them to the main floor. Alignment by as much as possible together in order to increase the signal level and power distribution within the block layer number, and appropriate adjustments to the alignment so that you can connect to the surface through-hole layout on the isolation block. Should be avoided in the PCB levels to generate free land, because they did pick up as a small antenna or into the noise. In most cases, if you can not link them to the main land, then you'd better remove them.