In die ontwerp van PCB-bord, met die vinnige toename in frekwensie, is daar baie inmenging wat anders is as dié van lae-frekwensie-printplaat. Boonop, met die toenemende frekwensie en die teenstrydigheid tussen die miniaturisering en die lae koste van die printplaat, word hierdie inmenging meer en meer ingewikkeld.

In die werklike navorsing kan ons tot die gevolgtrekking kom dat daar hoofsaaklik vier aspekte van interferensie is, insluitend geraas van kragtoevoer, transmissielyninterferensie, koppeling en elektromagnetiese interferensie (EMI). Deur die ontleding van verskillende interferensieprobleme van hoëfrekwensie-PCB en kombinasie met praktyk in die werk, word effektiewe oplossings voorgehou.

Eerstens, geraas van kragtoevoer

In die hoëfrekwensie -kring het die geraas van kragtoevoer ‘n duidelike invloed op die hoëfrekwensie -sein. Therefore, the first requirement of the power supply is low noise. Skoon vloere is net so belangrik soos skoon elektrisiteit. Hoekom? Die kragkenmerke word in figuur 1 getoon. Dit is duidelik dat die kragtoevoer ‘n sekere impedansie het, en die impedansie word oor die hele kragtoevoer versprei, daarom word die geraas by die kragtoevoer gevoeg.

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 -kringontwerp is dit in die meeste gevalle baie beter om die kragtoevoer as ‘n laag te ontwerp as as ‘n bus, sodat die lus altyd die pad van minimale impedansie kan volg.

Daarbenewens moet die kragbord ‘n seinlus bied vir alle gegenereerde en ontvangde seine op die PCB. Dit verminder die seinlus en verminder dus geraas, wat dikwels deur lae-frekwensie-kringontwerpers oor die hoof gesien word.

Hoëfrekwensie-PCB-ontwerp vind interferensie-oplossings plaas

Figuur 1: Kragseienskappe

Daar is verskillende maniere om kraggeluide in die PCB -ontwerp uit te skakel:

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. As die opening van die kragtoevoerlaag te groot is, sal dit die seinlus beïnvloed, die sein word verplig om te omseil, die lusoppervlakte neem toe en die geraas neem toe. At the same time, if several signal lines are clustered near the opening and share the same loop, the common impedance will cause crosstalk. Sien Figuur 2.

Hoëfrekwensie-PCB-ontwerp vind interferensie-oplossings plaas

Figuur 2: Algemene pad van bypass -seinlus

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. Analoge en digitale kragtoevoer om te skei: hoëfrekwensie-toestelle is oor die algemeen baie sensitief vir digitale geraas, dus moet die twee geskei word, by die ingang van die kragtoevoer aan mekaar gekoppel word, as die sein oor die analoog en digitale dele van die woorde, kan in die sein oor ‘n lus geplaas word om die lusarea te verminder. Die digitaal-analoog span wat vir die seinlus gebruik word, word in figuur 3 getoon.

Hoëfrekwensie-PCB-ontwerp vind interferensie-oplossings plaas

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.

Hoëfrekwensie-PCB-ontwerp vind interferensie-oplossings plaas

Figuur 4: Plaas die netsnoer langs die seinlyn

Two, transmission line

Daar is slegs twee moontlike transmissielyne in ‘n PCB:

Die grootste probleem van lintlyn en mikrogolflyn is refleksie. Besinning sal baie probleme veroorsaak. Byvoorbeeld, die lassein is die superposisie van die oorspronklike sein en die eggo -sein, wat die moeilikheidsgraad van seinanalise verhoog. Refleksie veroorsaak terugkeerverlies (terugkeerverlies), wat die sein net so erg beïnvloed as bykomende geraasinterferensie:

1. Die sein wat na die seinbron weerkaats word, verhoog die geraas van die stelsel, wat dit vir die ontvanger moeiliker maak om geraas van sein te onderskei;

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) Vermy die impedansie -diskontinuïteit van transmissielyne. Die punt van diskontinue impedansie is die punt van transmissielynmutasie, soos reguit hoek, deurgat, ens., Moet sover moontlik vermy word. Metodes: Om reguit hoeke van die lyn te vermy, so ver as moontlik om ‘n hoek van 45 ° of boog te kry, kan ‘n groot hoek ook wees; Gebruik so min as moontlik deurgate, want elke deurgat is ‘n impedansie -diskontinuïteit, soos in FIG. 5; Signals from the outer layer avoid passing through the inner layer and vice versa.

Hoëfrekwensie-PCB-ontwerp vind interferensie-oplossings plaas

Figure 5: Method for eliminating transmission line interference

(b) Do not use stake lines. Omdat enige stapellyn ‘n bron van geraas is. As die stapellyn kort is, kan dit aan die einde van die transmissielyn verbind word; As die stapellyn lank is, sal dit die hoof transmissielyn as die bron neem en groot refleksie lewer, wat die probleem sal bemoeilik. Dit word aanbeveel om dit nie te gebruik nie.

Derde, die koppeling

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.

Hoëfrekwensie-PCB-ontwerp vind interferensie-oplossings plaas

Figuur 6: Algemene impedansie -koppeling

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. Hierdie koppeling word aansienlik verminder, sodat die twee drade aan mekaar gedraai kan word om interferensie te verminder.

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. Die grootte van die induktiewe oorspraak hang af van die nabyheid van die twee lusse, die grootte van die lusarea en die impedansie van die las wat geraak word.

5. Koppeling van kragkabels: Die wisselstroom- of GS -kragkabels word deur elektromagnetiese steuring belemmer

Oordrag na ander toestelle.

There are several ways to eliminate crosstalk in PCB design:

1. Beide tipes oorspraak neem toe met die toename van die lasimpedansie, sodat die seinlyne wat sensitief is vir interferensie wat veroorsaak word deur oorspraak, behoorlik beëindig moet word.

2. Maksimaliseer die afstand tussen seinlyne om kapasitiewe oorspraak effektief te verminder. Grondbestuur, afstand tussen bedrading (soos aktiewe seinlyne en grondlyne vir isolasie, veral in die toestand van spring tussen die seinlyn en grond tot interval) en verminder loodinduktansie.

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. Vir sinvolle oorspraak moet die lusarea tot ‘n minimum beperk word, en indien toegelaat, moet die lus uitgeskakel word.

5. Avoid signal sharing loops.

6. Gee aandag aan seinintegriteit: die ontwerper moet eindes in die sweisproses implementeer om die seinintegriteit op te los. Ontwerpers wat hierdie benadering gebruik, kan fokus op die mikrostrooklengte van die afskermende koperfoelie om ‘n goeie prestasie van seinintegriteit te verkry. 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.

Daar is verskillende maniere om elektromagnetiese interferensie in PCB -ontwerp uit te skakel:

1. Verminder lusse: Elke lus is gelykstaande aan ‘n antenna, dus moet ons die aantal lusse, die oppervlakte van lusse en die antenna -effek van lusse tot ‘n minimum beperk. 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.

Hoëfrekwensie-PCB-ontwerp vind interferensie-oplossings plaas

Figuur 7: Filter tipes

3. The shielding. As gevolg van die lengte van die uitgawe plus baie besprekings wat artikels beskerm, nie meer ‘n spesifieke inleiding nie.

4. Reduce the speed of high-frequency devices.

5. Verhoog die diëlektriese konstante van die PCB -bord, wat kan voorkom dat die hoëfrekwensiedele soos transmissielyn naby die bord na buite uitstraal; 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. Noukeurig oorweegde bedrading en behoorlike beëindigings kan refleksies uitskakel.

3. Deurdagte bedrading en behoorlike beëindigings kan die kapasitiewe en induktiewe oorspraak verminder.

4. Ruisonderdrukking is nodig om aan die EMC -vereistes te voldoen.