Nevertheless, when be designed actually, truly practical skill is how cannot be restrained because of all sorts of designs when these criterion and law and eclectic processing undertake to them when accurate ground is carried out. Of course, a lot of important RF design a task to be worth to discuss, include impedance and impedance to match, insulation layer material is mixed cascade board and wavelengh and standing wave, the careful program that mastering premise of principle of of all kinds design to fall in the round is the assurance of one-time successful design.

 

The common problem that RF circuit designs

 

1, the interference between digital circuit module and imitate circuit module

 

If imitate circuit (radio frequency) work alone with digital circuit, may respective job is good. But, once put both,going up with a circuit board, use same power source works together, whole system is not stabilized probably. Because digital signal is in often,this basically is the ground and positive electricity source (> 3 V) between swing, and cycle is particularly short, often of accept second class. As a result of bigger amplitude and shorter switch time. Make these digital signal are included a large number of and independent the high frequency composition at switch frequency. In imitate part, from wireless tuning loop passes wireless equipment to receive partial signal to be less than LμV commonly. Because the difference between this number signal and radio frequency signal can achieve 120 DB. Apparent. If cannot make,digital signal and radio frequency signal depart well. Faint radio frequency signal may be destroyed, come so, wireless installation character of service can worsen, cannot work completely even.

 

2, the noise interference of power supply source

 

Radio frequency circuit is quite sensitive to power source noise, mix to burr voltage especially other and high frequency harmonic. Small controller can be inside cycle of every in-house clock short time sucks electric current of part of National People’s Congress suddenly, because contemporary small controller uses CMOS craft to make,this is. Accordingly. Assume a small controller moves with the in-house clock frequency of LMHz, it will extract electric current from power source with this frequency. If do not take appropriate power supply,go Ou. Be sure to cause the voltage burr on power supply cord. If these voltage burr arrive at the power source of circuit RF part to cite a base, serious when the likelihood brings about working be no longer in force.

 

3, unreasonable ground wire

 

If the ground wire processing of RF circuit is undeserved, the possibility arises a few strange phenomena. To digital circuit design, although do not have ground wire layer, function of most number circuit also is behaved good. And in RF frequency paragraph, although a very short ground wire also is met,be like inductor same function. Calculate roughly, the inductance quantity of every millimeter length is L NH about, the inductance of circuitry of the 10 Toni PCB when 433 MHz makes an appointment with 27Ω . If do not use ground wire layer, most ground wire will longer, circuit will not have the character of the design.

 

4, aerial is disturbed to the radiate of part of other imitate circuit

 

In PCB circuit design, board go up to still have other imitate circuit normally. For example, there is a model on a lot of circuit, several changeover (ADC) or converter of several ／ model (DAC) . Wei Wei Bian abandons the leech of R of excuse me of imitate Cong Piao that the high frequency signal that the antenna of radio frequency transmitter issues may arrive at ADC amaranth of model ability provide for fines silk illuminate signal of F of Zha of mail of tadpole of Wo of Ji lie ⒊ . If the processing of ADC input end is unreasonable, the self-excitation inside the ESD diode that RF signal may input in ADC. Cause ADC error thereby.

 

 

One, principle of layout of radio frequency circuit

 

When devising RF overall arrangement, must below preferential full enough a few total principles:

 

(1) an amplifier of as far as possible high power RF (HPA) with low noise amplifier (LNA) segregation leaves come, say simply, let high power RF launch circuit to be far from low power RF to receive circuit namely;

 

(2) ensure high power division has a whole land at least on PCB board, best above did not cross aperture, of course, copper Foil area has been jumped over greatly more;

 

(3) circuit and power source go Ou is same very important also;

 

(4) RF output needs to be far from RF input normally;

 

(5) sensitive imitate signal should be far from signal of high speed number and RF letter as far as possible;

 

2, physical partition, electric partition designs partition

 

Can decompose for physical partition and electric partition. Physical partition basically involves the issue such as layout of yuan of parts of an apparatus, front and screen; Electric partition can continue to decompose the partition that walks along line, sensitive circuit and signal and ground connection to wait for power source allocation, RF.

 

1, we discuss physical partition issue

 

Yuan layout of parts of an apparatus is the key that realizes design of an outstanding RF, the most effective technology is yuan of parts of an apparatus that originallies to be located in RF method to go up surely above all, adjust its front to be decreased with the length RF method the smallest, make the input is far from output, depart far as far as possible high power circuit and low power circuit.

 

The most effective circuit board pile method is will advocate ground plane (advocate the ground) the 2nd when arrangement falls in surface layer, take RF line on surface layer as far as possible. The dimension crossing aperture that gets on RF method is decreased the smallest can reduce method inductance not only, and still can decrease advocate the empty solder dot on the ground, can reduce RF energy leak to arrive inside cascade board the opportunity of other area. On physical space, like multistage amplifier normally enough general keeps apart such linear circuit to come each other between many RF area, but diplexer, first detector and intermediate frequency amplifier / first detector always has many RF/IF signal to be disturbed each other, because this must take care,the ground reduces this one effect the smallest.

 

2, RF and IF walk along a line to should walk along crossed across as far as possible, lie between a ground between them as far as possible

 

Right RF way to making the property of a PCB board character is very main, this namely why yuan layout of parts of an apparatus in the mobile phone normally PCB board is designed in the account that takes major time. In the mobile phone PCB board is designed, can put circuit of low noise amplifier normally the some face of PCB board, and high power amplifier is put in other one side, be in them finally through diplexer on same area on the antenna that joins RF end and base band processor are carried. Need a few skill to ensure pass aperture continuously won’t RF energy from board deliver another at the same time, commonly used technology is use blind opening in two sides. Can pass will direct arrangement crossing aperture to be in the adverse effect that the area that PCB board two sides does not get RF to disturb will come to to will pass aperture continuously is decreased the smallest.

 

Be in unlikelily sometimes many circuit piece between assure enough segregation, must consider to use metallic screen cover to be screen of radio frequency energy inside RF area below this kind of circumstance, metallic screen is overspread must solder is on the ground, must with yuan parts of an apparatus maintains a suitable space, because this need takes up precious PCB board space. What make sure screen is overspread as far as possible is complete and special important, the digital line that enters metallic screen cover should go lining as far as possible, and had better take line layer below a PCB is layer. The little gap that RF line can overspread bottom from metallic screen and the wiring that ground breach is in are walked out of on the layer, as far as possible much cloth wants all round breach place nevertheless a few ground, the ground on different layer can be passed many cross Kong Lian to be together.

 

3, appropriate go with significant chip power source Ou is very important also

 

A lot of compositive the RF chip of linear circuitry is very sensitive to the noise of power source, normally every chip needs to use be as high as 4 capacitance and inductance of a segregation to ensure filter divides all power source noise. An integrated circuit or amplifier often contain to open leakage pole output, because this needs to go up,pull inductance to provide load of RF of a tall impedance and direct current source of a low impedance, the power source that same principle also applies to pair of this one inductance to carry undertakes going Ou.

 

Some chip need ability of many power source to work, accordingly you may need two will part to undertake to them Ou is handled going to 3 capacitance and inductance, inductance seldom runs paralell lean together, because this will form transformer of an empty core,generation of mutual induction disturbs signal, accordingly the distance between them should be equivalent to at least among them the height of a parts of an apparatus, perhaps arrange into right angle arrive with decreasing its mutual inductance the smallest.

 

4, substantially of electric and divisional principle and physical partition are identical, but still contain element of a few other

 

The certain part of the mobile phone uses different job tension, and software of have the aid of undertakes controlling to its, in order to prolong batteries work life. This means a mobile phone to need to run a variety of power source, and this brought more issues to segregation.

 

Power source introduces from connector normally, undertake Ou processing divides any coming from with filter going instantly circuit board is external noise, next repass undertakes allocation to its after a group of switch or manostat. Mobile phone PCB board go up the dc electric current of most circuit is quite small, because this walks along line width,not be a problem normally, nevertheless, must walk along alone for the power source of high power amplifier as far as possible wide big report streamline, press with will be being transmitted fall decrease lowest. To avoid loss of too much electric current, need is used many cross Kong Lai to transmit electricity another from some layer. In addition, if cannot be in,the power source of high power amplifier brings crural end to undertake going adequately to it Ou, noise of so high power will radiation goes to whole board on, bring various issues.

 

The ground connection of high power amplifier is quite crucial, often need to design cover of screen of a metal for its. Pay close attention to date of public of filter small letter: Filter_CN, aid you further upward, below most circumstance, likewise crucial is to ensure RF output is far from RF input. This also applies to amplifier, bumper and filter. Below worst circumstance, if amplifier is mixed the output of bumper with proper phasic input end to theirs with amplitude feedback, so they produce self-oscillation likely. Below best circumstance, their aux will be able to leaves steadily job in any temperature and voltage condition.

 

Actually, they may become not stable, add noise and intermodulation signal to RF signal. If radio frequency line must carry retrace to output end from the input of filter, this may damage the belt of filter badly to know character. Get good segregation to make input and be outputted, must be above all all round filter cloth circuit ground, next area of filter lower level also wants cloth together, and with around filter advocate ground join rises. Be far from the line that needs to cross filter as far as possible filter cites a base also is a good method.

 

In addition, whole board on the ground connection of each places wants very careful, can be in otherwise introduce channel of a coupling. Can choose Chan Duan sometimes or balance RF line, about across the principle of interference and EMC/EMI is here likewise applicable. If balance RF line takes the word with right string, can reduce noise and alternate interference, but their impedance is compared normally tall, and should hold a reasonable line wide in order to get one matchs the signal source, impedance that takes line and load, actual wiring may have a few difficulty. Bumper can be used improve segregation result, because of it but same cent is a signal two parts, use at the circuit with different drive, especially this brace up the likelihood needs bumper to come drive many first detector.

 

Arrive in RF frequency place when first detector in all when the model keeps apart condition, it will not work normally. Bumper can keep apart the impedance change that different frequency manages well, won’t disturb each other between circuit thereby. Bumper is very big to the help of the design, they are OK follow closely is in need by drive circuit at the back of, make high power outputs a line thereby very short, because the input signal n of bumper is lower, accordingly they are opposite not easily board the other circuit that go up causes interference. Pressure accuse an oscillator (VCO) the frequency that can be voltage changeover of change change, this one character is used at switch of high speed channel, but the minim noise changeover that they also get on control voltage likewise changes for tiny frequency, and this increased noise with respect to signal giving RF.

 

5, want guarantee against to increase noise to must consider from the following respects

 

Above all, the expectation frequency wide range of control line is likely from DC till 2MHz, and come through filter wave take out is so broadband the noise of the belt is impossible almost; Next, VCO control line is the one part of a feedback return circuit that dominates frequency normally, it introduces noise likely in a lot of places, accordingly must control line of VCO of special tread lightly. Want the ground is sincere to ensure RF walks along line lower, and all yuan parts of an apparatus arrives firmly repeatedly advocate on the ground, the segregation taking a line that brings noise possibly with other leaves come.

 

In addition, should ensure the power source of VCO already got going adequately Ou, because the RF output of VCO often is relative to taller n, VCO outputs signal to disturb other circuit very easily, because this must is opposite,VCO tries special attention. In fact, VCO often the fag end that cloth puts in RF area, sometimes it still needs cover of screen of a metal. Syntonic circuit (use at catapult, another is used at receiver) concern with VCO, but the characteristic that also has itself. Tell simply, syntonic circuit is a collateral and syntonic circuit that contains the diode that allow a gender, it conduces to a setting VCO job frequency and get on speech or data modulation to RF signal. The design principle of all VCO applies to syntonic circuit likewise. Because syntonic circuit contains quantitative quite a few yuan parts of an apparatus, board on distributinging area is wider and move below a very tall RF frequency normally, because this is syntonic,circuit is opposite normally noise is very sensitive.

 

Signal arranges the photograph adjacent foot in chip to go up normally, but these signal bring a foot to need again with cooperate ability to work relative to bigger inductance and capacitance, this asks the position of these inductance and capacitance must lean very nearly conversely, return a very sensitive to noise operating ring road to go up repeatedly. Should be being accomplished is this bit not easy.

 

Automatic gain control (AGC) amplifier is a place that gives an issue easily likewise, no matter be,blast off or receive circuit to be able to have AGC amplifier. Normally effectively filter drops AGC amplifier noise, because the mobile phone has processing,blast off nevertheless and receive the ability that signal intensity changes quickly, because this asks AGC circuit has a quite wide bandwidth, and this makes the AGC amplifier on certain and crucial circuit introduces noise very easily. Design AGC circuitry must abide by good imitate circuit to design a technology, and this puts an input to bring foot and very short feedback way to concern with very short carry, this two place must be far from RF, IF or signal of high speed number takes a line.

 

Same, good grounding is necessary also, and the power source of chip must get going goodly Ou. If must want to carry in input or output long term, had better be so carry in output, the impedance that outputs end normally wants low much, and noise of not easy also induction. Signal n is normally taller, introduce noise more easily to other circuit. In all PCB design, be far from digital circuit imitate circuit as far as possible is a total principle, it also applies to RF PCB design likewise. Communal imitate ground and be being used at screen and the ground that separate line is coequal and important normally, because this is designing inchoate phase, layout of yuan of parts of an apparatus with careful plan, comprehensive consideration and complete layout * appraise are very important, should make RF line great distance is mixed from imitate circuitry likewise a few very crucial number signal, all RF walk along Pan Heyuan of line, solder all round should fill skin of ground connection copper more as far as possible, and as far as possible with advocate the ground is linked together. If RF walks along a line to must cross line, so walk along line cloth along RF between them as far as possible one layer and advocate the ground that the ground is linked together. If impossible word, must make sure they are crossed across, this can decrease the coupling that allow a gender the smallest, take a line in every RF as far as possible at the same time all round much cloth a few ground, go to them repeatedly advocate the ground.

 

In addition, will collateral RF walks along the distance between the line to be decreased the smallest can decrease perceptual coupling the smallest. Whole ground plane of a sincere is put when the ground floor below surface layer directly, segregation effect is best, although take care,the practice of the other when a bit design also is in charge of with. Be in each of PCB board, should on cloth as far as possible much ground, go to them repeatedly advocate the ground. As far as possible the plot measure that takes a line to rely on together to allocate a layer in order to increase in-house signal layer and power supply, so that you can have joined the ground aperture decorates the segregation plot to surface layer,adjust a line appropriately. Ought to avoid to be in PCB makes free land on the layer each, because they can resemble a small antenna in that way collect or infuse noise. Below most circumstance, if you cannot connect them advocate the ground, so you are best their take out.

 

3, a few respects should note when PCB board is designed

 

1, the processing of power source, ground wire

 

Make be in already whole PCB board medium wiring is finished very well, but the consideration as a result of power source, ground wire is not considerate and the interference that cause, can make the function of the product drops, affect the successful rate of the product even sometimes. Want to be treated seriously to the wiring of report, ground wire so, fall the noise interference that place of report, ground wire generates to lowermost limit, in order to assure the quality of the product. The project that pursues electronic products plan to every understands the reason that noise place produces between ground wire and power supply cord for personnel, make to reducing type to restrain noise only now in order to state:

 

(1) , well-known is Ou electric capacity is increased between power source, ground wire.

 

(2) , as far as possible width of broaden power source, ground wire, had better be ground wire wider than power supply cord, their relation is: Line of ＞ of power supply cord, line is normally broad for: 0.2 ～ 0.3mm, can amount to 0.05 ～ 0.07mm via fine width most, power supply cord is 1.2 ～ 2.5 Mm. The PCB of logarithm word circuit can use wide ground lead to form a loop, form an earth mat to use namely (the ground of imitate circuit cannot be used so)

 

(3) , make ground wire use with layer of large area copper, join the place that was not used with ground photograph on printed board use as ground wire. Or it is make it multilayer board, power source, ground wire takes up each.

 

2, the in all processing of digital circuit and imitate circuit

 

There are a lot of PCB now is single function circuit no longer (number or imitate circuit) , mix by digital circuit and imitate circuit however form. Because this needs a consideration when wiring,the problem is disturbed each other between them, noise disturbs especially on-line. The frequency of digital circuit is tall, the susceptibility of imitate circuit is strong, to line, high frequency line is far from sensitive imitate circuit parts of an apparatus as far as possible, to ground wire, give others a hard time PCB has a node only to the outside, must undertake handling number, model in PCB interior so in all the problem of the ground, and be in board in-house number ground and imitate ground are apart actually between them each other disconnect, just be in in PCB and outside connective interface (if insert first class) . Digital ground and imitate ground have a bit short receive, ask an attention, only one connects contact. Also have go up in PCB not in all, this is decided by systematic design.

 

3, line cloth is in report (the ground) on the layer

 

Be in multilayer when printed board wiring, because be in,the line that line layer is over without cloth is remained already not much, add number of plies to be able to cause waste to also can increase certain workload to production more again, cost also raised accordingly, to resolve this contradiction, can consider to be in report (the ground) wiring undertakes on the layer. Should consider to use power source layer above all, just be layer next. Because had better be the integrality of reservation layer.

 

4, the processing of leg of the join in large area conductor

 

The ground connection that accumulates in bedding face (report) in, commonly used the leg of yuan of parts of an apparatus joins with its, have integrated consideration to joining the processing of the leg needs, electric function, the solder of component leg dish receive completely with cupreous range had better, but to component solder assemble with respect to existence a few undesirable hidden trouble are like: ① solders need high-power heater. ② causes empty solder drop easily. So electric function and craft need give attention to two or morethings, make it cross spends solder dish, the segregation is heat that say (Heat Shield) common says to heat up solder dish (Thermal) , such, when can making soldering because of sectional the possibility that be heated up dispersedly too and produces empty solder drop decreases greatly. Multilayer board receive report (the ground) the processing of layer leg is identical.

 

5, the action of system of the network in wiring

 

In a lot of CAD systems, wiring decides according to network system. Reseau is too close, although access increases somewhat, but the pace is entered too small, the data bulk of graph field is too great, this has higher demand to the space putting store of equipment necessarily, at the same time also target computer kind the operation speed of electronic product has huge effect. And some access are invalid, be like by the solder of component leg dish take up or by installing hole, calm people aperture place takes up etc. Reseau is too scanty, access knows the effect of rate too less to cloth great. Want to the reseau system with a sound density comes to those who support wiring to undertake so. Standard yuan the distance between two legs is parts of an apparatus 0.1 inches (2.54mm) , so the foundation of reseau system is 0.1 inches surely commonly (2.54 Mm) or the whole multiple that is less than 0.1 inches, be like: 0.05 inches, 0.025 inches, 0.02 inches wait.

 

 

4, skill of design of high frequency PCB and method

 

1, transmission line corner should use 45° part, in order to reduce a damage

 

2, should use insulation constant value to press the high-powered insulation circuit with strict and controlled administrative levels board. This kind of method is helpful for the electric magnetic field between pair of insulating material and adjacent wiring undertaking administrative effectively.

 

3, the PCB that should perfect concerned high accuracy to etch designs a standard. Should consider to stipulate wide total error is the line + / – 0.0007 inches, to wiring appearance next cutting (Undercut) undertake administrative with cross section and appoint wiring sidewall to eletroplate condition. To wiring (lead) geometrical appearance and coating surface undertake overall managing, it is quite important to implement these standards to solving the problem of hasten skin effect related to microwave frequency to reach.

 

4, inductance of take a percentage of a deal of outstanding down-lead existence, want to avoid to use the component that has lead. Below high frequency environment, best use surface installs package.

 

5, cross aperture to signal and character, should avoid to be in sensitive board on had used Kong Jia to be versed in (Pth) craft, because this craft can have brought about inductance of down-lead of aperture place generation.

 

6, should offer rich ground connection layer. Should use mould pressing aperture to receive these layer join to rise prevent field of 3 dimension electromagnetism to be opposite the influence of circuit board.

 

7, want choice blame to electroanalysis plating nickel or dip are aureate craft, do not use HASL law to undertake eletroplating.

 

8, the flow that block solder layer can prevent soldering tin to cream. But, as a result of the sealed sex of ply uncertainty and insulation property, whole board the bigger change that the surface covers block solder material to will bring about microstrip to design medium electromagnetism energy. Use solder dam commonly (Solder Dam) come the electromagnetism field of block solder layer.

 

Below this kind of circumstance, we are managing microstrip to arrive the changeover between coaxial cable. In coaxial cable, ground wire layer is annular interweave, and removed and even. In microstrip, ground connection layer is under active line. This introduced certain edge effect, the understanding when needing to be being designed, forecast and try to consider. Of course, this kind does not match to also can cause a damage, must the oldest rate reduces this kind not to match to be disturbed in order to avoid generation noise and signal.

 

5, electromagnetism compatibility design

 

Electromagnetism compatibility is to point to electronic equipment to still can have working capacity effectively in all sorts of electromagnetism environments. The purpose that electromagnetism compatibility designs is to make electronic equipment can restrain all sorts of foreign interference already, make electronic equipment can work normally in specific electromagnetism environment, can reduce electronic equipment itself to be disturbed to the electromagnetism of other electron equipment again at the same time.

 

1, the lead width with logical choice

 

Because twinkling changes,electric current is disturbed in the concussion that prints generation of the place on line basically is caused by the inductance composition that prints lead, because this answers,reduce the inductance that prints lead to measure as far as possible. The inductance quantity that prints lead and its length become direct ratio, with its width becomes inverse ratio, short and the lead of essence of life is consequently right restraining interference is advantageous. The line of driver of clock down-lead, travel or bus line driver often carries great very short time to change electric current, print lead to want as far as possible short. To discrete element circuit, when printing lead width to be controlled in 1.5mm, can satisfy a requirement completely; To integrated circuit, print lead width to be able to choose between 0.2 ～ 1.0mm.

 

2, use right wiring strategy

 

Use equality to walk along a line to be able to reduce lead inductance, but the mutual inductance between lead increases with distributinging capacitance, if layout allows, had better use well glyph meshy wiring structure, the one side that particular way is printed board is transverse wiring, another fore-and-aft wiring, use plated through hole to be linked together in alternate aperture place next.

 

3, restrain string of faze effectively

 

To restrain string of faze between printed board lead, the equality that should avoid Sunday run as far as possible when designing wiring takes a line, pull open the distance between line and line as far as possible, line and ground wire and power supply cord as far as possible not across. What a ground connection installs between very sensitive line is disturb to print a line in a few pairs, restrain string of faze effectively.

 

4, the electromagnetism radiate that passes the generation when printing lead to avoid high frequency signal, in printed circuit board when wiring, still should notice the following:

 

(1) reduce the discontinuous sex that prints lead as far as possible, for example lead width is not choppy, the corner of lead should be more than 90 degrees to prohibit cricoid walk along a line to wait.

 

(2) clock signal down-lead produces electromagnetism radiate the most easily to disturb, when taking a line, should stand by with photograph of ground wire loop, driver should be tightened be next to connector.

 

(3) bus line driver should be endured closely its desire the bus line of drive. Leave printed circuit to those board down-lead, driver should be next to connector closely.

 

(4) the wiring of data bus line should place ground wire of a signal between every two line. Had better be to be next to main least of all address catalyst to set ground return closely, because latter Chang Zai has high frequency electricity.

 

(5) high speed, middling speed and low speed logic are decorated in printed board when circuit, should according to the graph the means of 1 arranges parts of an apparatus.

 

5, restrain reflection to disturb

 

To restrain a reflex that prints line terminal now to disturb, besides special need, should shorten as far as possible the length that prints a line and use slow fast circuit. Can add terminal to match when necessary, mix rightly in the extreme of transmission line namely power source end adds those who receive value of a same block to match resistor each. According to experience, faster to average rate TTL circuit, its print line to grow to should use terminal to match measure at 10cm above. Match the block value of resistor to answer according to the output of integrated circuit drive electric current and the maximum that absorb electric current decide.

 

6, circuit board uses strategy of wiring of the line that need branch in design process

 

Special close differs wiring minute of signal is right mutual between also can mutual close together coupling, this kind mutual the coupling between can reduce EMI to blast off, normally (also have a few exception of course) the signal that need branch also is high speed signal, so high speed designs regulation to also apply to the wiring of the signal that need branch normally, it is such more when the line that designs transmission line especially. This means us must the wiring of line of design of very careful ground, in order to ensure the line of diagnostic impedance edge of line everywhere successive and maintain a constant.

 

In the layout wiring process that is opposite in the line that need branch, we hope to differ the two PCB line in dividing a line to be opposite to agree completely. This is meant, the impedance that the PCB line in in applying actually, should making great effort to ensure the string that need branch is right has just the same and the length of wiring agrees completely also. Line of the PCB that need branch always is didymous wiring normally, and the way with the distance right along the line between them maintains in aleatoric position for invariable and changeless. Normally the circumstance falls, difference divides the layout wiring with right string to always be stood by as far as possible.