Di sêwirana Board PCB, Bi zêdebûna bilez a frekansê, dê gelek mudaxeleyên ku ji ya tabloya PCB-ya bi frekansa nizm cuda ne, hebin. Digel vê yekê, bi zêdebûna frekansê û nakokiya di navbera piçûkbûn û lêçûna kêm a panel PCB de, ev destwerdan dê her ku diçe aloztir bibe.

In the actual research, we can conclude that there are mainly four aspects of interference, including power supply noise, transmission line interference, coupling and electromagnetic interference (EMI). Bi analîzkirina cûrbecûr pirsgirêkên navbeynkariya PCB-ya bi frekansa bilind û bi hev re bi pratîka di xebatê de, çareseriyên bandorker têne pêş.

Pêşîn, dengê dabînkirina hêzê

Di pêla frekansa bilind de, dengê peydakirina hêzê bandorek eşkere li ser îşareta frekansa bilind heye. Therefore, the first requirement of the power supply is low noise. Clean floors are just as important as clean electricity. Why? The power characteristics are shown in Figure 1. Eşkere ye ku, dabînkirina hêzê astengiyek heye, û impedans li seranserê dabînkirina hêzê tê belav kirin, ji ber vê yekê, dê deng li dabînkirina hêzê were zêdekirin.

Then we should minimize the impedance of the power supply, so it is best to have a dedicated power supply layer and grounding layer. In hf circuit design, it is much better to design the power supply as a layer than as a bus in most cases, so that the loop can always follow the path of minimal impedance.

In addition, the power board must provide a signal loop for all generated and received signals on the PCB. This minimizes the signal loop and thus reduces noise, which is often overlooked by low-frequency circuit designers.

Sêwirana PCB-ya bi frekansa bilind çareseriyên destwerdanê pêk tê

Wêne 1: Taybetmendiyên hêzê

Gelek awayên rakirina dengê hêzê di sêwirana PCB de hene:

1. Note the through hole on the board: the through hole requires etched openings on the power supply layer to leave space for the through hole to pass through. If the opening of the power supply layer is too large, it is bound to affect the signal loop, the signal is forced to bypass, the loop area increases, and the noise increases. At the same time, if several signal lines are clustered near the opening and share the same loop, the common impedance will cause crosstalk. Mêjû 2 binêrin.

Sêwirana PCB-ya bi frekansa bilind çareseriyên destwerdanê pêk tê

Figureikil 2: Rêya hevbeş a çembera sînyala baypasê

2. The connection line needs enough ground: each signal needs to have its own proprietary signal loop, and the loop area of the signal and loop is as small as possible, that is to say, the signal and loop should be parallel.

3. Dabeşkirina hêzê ya analog û dîjîtal ji hev veqetandinê: cîhazên bi frekansa bilind bi gelemperî ji dengê dîjîtal re pir hesas in, ji ber vê yekê divê her du ji hev bêne veqetandin, di deriyê dabînkirina hêzê de bi hev ve bêne girêdan, ger îşaret li seranserê perçeyên analog û dîjîtal ên peyvan, dikare di sînyala li seranserê xelek were bicîh kirin da ku qada loop kêm bike. Dirêjahiya dîjîtal-analog ku ji bo çiraya îşaretê tê bikar anîn di Figure 3 de tê xuyang kirin.

Sêwirana PCB-ya bi frekansa bilind çareseriyên destwerdanê pêk tê

Figure 3: Digital – analog span for signal loop

4. Avoid overlapping of separate power supplies between layers: otherwise circuit noise can easily pass through parasitic capacitive coupling.

5. Isolate sensitive components: such as PLL.

6. Place the power cable: To reduce the signal loop, place the power cable on the edge of the signal line to reduce the noise, as shown in Figure 4.

Sêwirana PCB-ya bi frekansa bilind çareseriyên destwerdanê pêk tê

Wêne 4: Corda hêzê li kêleka xeta îşaretê bicîh bikin

Two, transmission line

Di PCB -yê de tenê du xetên veguheztinê hene:

Pirsgirêka herî mezin a xêzika ribbon û xeta mîkrovalê raçavkirin e. Refleksyon dê bibe sedema gelek pirsgirêkan. Mînakî, sînyala barkirinê dê bibe berhevoka nîşana orîjînal û nîşana echo, ku dê dijwariya analîzkirina îşaretê zêde bike. Refleks dibe sedema windabûna vegerê (windabûna vegerê), ku bandorê li sînyala bi qasî xirabiya navbeynkariya additive dike:

1. Nîşana ku li çavkaniya îşaretê tê xuyang kirin dê dengê pergalê zêde bike, û ji wergirê re dijwar dike ku deng ji îşaretê cuda bike;

2. Any reflected signal will basically degrade the signal quality and change the shape of the input signal. Generally speaking, the solution is mainly impedance matching (for example, the impedance of the interconnection should very match the impedance of the system), but sometimes the calculation of impedance is more troublesome, you can refer to some transmission line impedance calculation software. The methods of eliminating transmission line interference in PCB design are as follows:

(a) Avoid impedance discontinuity of transmission lines. Nuqteya impedance ya bêserûber xala mutasyona xeta veguhastinê ye, wek goşeya rasterast, di nav çalê de, û hwd., Divê heya ku ji dest tê were dûr xistin. Rêbaz: Ji bo ku ji goşeyên rasterast ên xetê dûr nekevin, heya ku ji dest tê 45 ° Angle an arc, Angle mezin jî dikare bibe; Use as few through holes as possible, because each through hole is an impedance discontinuity, as shown in FIG. 5; Signals from the outer layer avoid passing through the inner layer and vice versa.

Sêwirana PCB-ya bi frekansa bilind çareseriyên destwerdanê pêk tê

Figure 5: Method for eliminating transmission line interference

(b) Do not use stake lines. Ji ber ku her xêzek pile çavkaniyek deng e. Ger xeta pileyê kurt be, ew dikare li dawiya xeta veguhastinê were girêdan; Ger xeta pile dirêj be, ew ê xeta veguhastinê ya sereke wekî çavkaniyê bigire û bertekek mezin bide, ku dê pirsgirêkê aloztir bike. Tête pêşniyar kirin ku wê bikar neynin.

Ya sêyemîn, hevberdan

1. Common impedance coupling: it is a common coupling channel, that is, the interference source and the interfered device often share some conductors (such as loop power supply, bus, and common grounding), as shown in Figure 6.

Sêwirana PCB-ya bi frekansa bilind çareseriyên destwerdanê pêk tê

Figure 6: Common impedance coupling

In this channel, the drop back of the Ic causes a common-mode voltage in the series current loop, affecting the receiver.

2. The field common-mode coupling will cause the radiation source to cause common-mode voltages in the loop formed by the interfered circuit and on the common reference surface.

If the magnetic field is dominant, the value of the common-mode voltage generated in the series ground circuit is Vcm=-(△B/△t)* area (where △B= change in magnetic induction intensity). If it is an electromagnetic field, when its electric field value is known, its induced voltage: Vcm=(L* H *F*E)/48, the formula is suitable for L(m)=150MHz, beyond this limit, the calculation of the maximum induced voltage can be simplified as: Vcm=2* H *E.

3. Differential mode field coupling: refers to the direct radiation by wire pair or circuit board on the lead and its loop induction received. If you get as close to the two wires as possible. Ev hevberdan pir kêm dibe, ji ber vê yekê her du têl dikarin bi hev re werin zivirandin da ku navbeynkariyê kêm bikin.

4. Inter-line coupling (crosstalk) can cause unwanted coupling between any line or parallel circuit, which will greatly damage the performance of the system. Its type can be divided into capacitive crosstalk and perceptual crosstalk.

The former is because the parasitic capacitance between the lines makes the noise on the noise source coupled to the noise receiving line through current injection. The latter can be thought of as the coupling of signals between the primary stages of an unwanted parasitic transformer. Mezinahiya xaçepirsa induktîf bi nêzîkbûna du xelekan, mezinahiya devera loopê, û impedansa barkirinê ya ku bandor dibe ve girêdayî ye.

5. Hevberdana kabloya hêzê: Kabloyên hêza AC an DC bi navbeynkariya elektromagnetîkî ve têne asteng kirin

Transfer to other devices.

There are several ways to eliminate crosstalk in PCB design:

1. Both types of crosstalk increase with the increase of load impedance, so the signal lines sensitive to interference caused by crosstalk should be properly terminated.

2. Dûrahiya di navbera xetên îşaretê de herî zêde bikin da ku xaçerêya kapasîteyî bi bandor kêm bike. Birêvebirina axê, dûrbûna di navbera têlkirinê de (wek xetên îşaretê yên çalak û xêzên axê ji bo veqetandinê, nemaze di rewşa ketina di navbera xeta îşaretê û erd heya navberê de) û kêmkirina induktasyona rê.

3. Capacitive crosstalk can also be effectively reduced by inserting a ground wire between adjacent signal lines, which must be connected to the formation every quarter of a wavelength.

4. Ji bo xaçepirsiya maqûl, divê quncika çerxê were kêm kirin, û ger destûr were dayîn, divê çop were rakirin.

5. Avoid signal sharing loops.

6. Bala xwe bidin yekseriya îşaretê: sêwiraner pêdivî ye ku di pêvajoya weldingê de dawiyan pêk bîne da ku yekseriya îşaretê çareser bike. Designers using this approach can focus on the microstrip length of the shielding copper foil in order to obtain good performance of signal integrity. For systems with dense connectors in the communication structure, the designer can use a PCB as the terminal.

Four, electromagnetic interference

As the speed increases, EMI becomes more and more serious and presents in many aspects (such as electromagnetic interference at interconnects). High-speed devices are particularly sensitive to this and will receive high-speed spurious signals, while low-speed devices will ignore such spurious signals.

There are several ways to eliminate electromagnetic interference in PCB design:

1. Çêlokan kêm bikin: Her loopek bi antenek re ye, ji ber vê yekê em hewce ne ku hejmara pêl, qada pêl û bandora antenayê ya qulikan kêm bikin. Make sure the signal has only one loop path at any two points, avoid artificial loops and use the power layer whenever possible.

2. Filtering: Filtering can be used to reduce EMI on both the power line and the signal line. There are three methods: decoupling capacitor, EMI filter and magnetic element. EMI filter is shown in Figure 7.

Sêwirana PCB-ya bi frekansa bilind çareseriyên destwerdanê pêk tê

Wêne 7: Cureyên Parzûnê

3. The shielding. Di encama dirêjahiya mijarê de û gelek gotarên mertalê gotûbêjê, êdî pêşgotinek taybetî.

4. Reduce the speed of high-frequency devices.

5. Berdewamiya dielektrîk a tabloya PCB -yê zêde bikin, ku dikare pêşî li tîrêjên derve yên perçeyên frekansa bilind ên wekî xeta veguhastinê ya li nêzî panelê bigire; Increase the thickness of PCB board, minimize the thickness of microstrip line, can prevent electromagnetic line spillover, can also prevent radiation.

At this point, we can conclude that in hf PCB design, we should follow the following principles:

1. Unification and stability of power supply and ground.

2. Carefully considered wiring and proper terminations can eliminate reflections.

3. Carefully considered wiring and proper terminations can reduce capacitive and inductive crosstalk.

4. Ji bo bicihanîna pêdiviyên EMC pêdivî bi tepisandina deng heye.