Yn it ûntwerp fan PCB-boerd, mei de rappe ferheging fan frekwinsje, sil d’r in protte ynterferinsje wêze dy’t ferskilt fan dy fan leechfrekwinsje PCB-boerd. Boppedat, mei de tanimmende frekwinsje en de tsjinstelling tusken de miniaturisaasje en lege kosten fan PCB -boerd, sille dizze ynterferinsje mear en mear yngewikkeld wurde.

Yn it eigentlike ûndersyk kinne wy ​​konkludearje dat d’r foaral fjouwer aspekten binne fan ynterferinsje, ynklusyf lûd fan stroomfoarsjenning, ynterferinsje fan transmissielinen, koppeling en elektromagnetyske ynterferinsje (EMI). Troch it analysearjen fan ferskate ynterferinsjeproblemen fan PCB mei hege frekwinsje en kombinearjen mei praktyk yn wurk, wurde effektive oplossingen nei foaren brocht.

Earst, lûd fan stroomfoarsjenning

Yn it hege frekwinsjekring hat it lûd fan stroomfoarsjenning in foar de hân lizzende ynfloed op it sinjaal fan ‘e hege frekwinsje. Therefore, the first requirement of the power supply is low noise. Skjin flierren binne like wichtich as skjinne elektrisiteit. Wêrom? De krêftkenmerken wurde werjûn yn figuer 1. Fansels hat de stroomfoarsjenning in bepaalde impedânsje, en is de impedânsje ferdield oer de heule stroomfoarsjenning, dêrom sil it lûd wurde tafoege oan ‘e stroomfoarsjenning.

Then we should minimize the impedance of the power supply, so it is best to have a dedicated power supply layer and grounding layer. Yn hf -circuitûntwerp is it yn ‘e measte gefallen folle better de stroomfoarsjenning as in laach te ûntwerpen dan as in bus, sadat de lus altyd it paad fan minimale impedânsje kin folgje.

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.

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Figuer 1: Power skaaimerken

D’r binne ferskate manieren om stroomlûd yn PCB -ûntwerp te eliminearjen:

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. Sjoch figuer 2.

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Figuer 2: Mienskiplik paad fan bypass -sinjaallus

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 stroomfoarsjenning om te skieden: apparaten mei hege frekwinsje binne oer it algemien heul gefoelich foar digitaal lûd, dus de twa moatte wurde skieden, tegearre ferbûn by de yngong fan ‘e stroomfoarsjenning, as it sinjaal oer de analoge en digitale dielen fan’ e wurden, kinne wurde pleatst yn it sinjaal oer in loop om it lusgebiet te ferminderjen. De digitaal-analoge span brûkt foar de sinjaallus wurdt werjûn yn figuer 3.

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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.

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Figuer 4: Plak it netsnoer neist de sinjaalline

Two, transmission line

D’r binne mar twa mooglike transmisjeline yn in PCB:

It grutste probleem fan lintline en magnetronline is refleksje. Refleksje sil in protte problemen feroarsaakje. Bygelyks, it ladesignaal sil de superposysje wêze fan it orizjinele sinjaal en it echosignaal, wat de muoite fan sinjaalanalyse sil ferheegje. Refleksje feroarsaket weromferlies (weromferlies), wat it sinjaal sa bot beynfloedet as tafoegjende lûdinterferinsje:

1. It sinjaal werom reflekteare nei de sinjaalboarne sil it lûd fan it systeem ferheegje, wêrtroch it lestiger wurdt foar de ûntfanger om lûd te ûnderskieden fan sinjaal;

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) Foarkom diskontinuïteit fan impedânsje fan transmissielinen. It punt fan diskontinue impedânsje is it punt fan mutaasje fan transmissjeline, lykas rjochte hoeke, troch gat, ensfh., Moat sa fier mooglik wurde foarkommen. Metoaden: Om rjochte hoeken fan ‘e line te foarkommen, sa fier mooglik 45 ° Hoek of bôge te gean, kin grutte hoeke ek wêze; Brûk sa min mooglik trochgatten, om’t elk trochgeande gat in diskontinuïteit is fan impedânsje, lykas werjûn yn FIG. 5; Signals from the outer layer avoid passing through the inner layer and vice versa.

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Figure 5: Method for eliminating transmission line interference

(b) Do not use stake lines. Om’t elke pealline in boarne is fan lûd. As de pealline koart is, kin dizze wurde ferbûn oan ‘e ein fan’ e transmissieline; As de pealline lang is, sil it de haadtransmissieline as de boarne nimme en grutte refleksje produsearje, wat it probleem komplisearje sil. It is oan te rieden it net te brûken.

Tredde, de keppeling

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.

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Figuer 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. Dizze koppeling wurdt sterk fermindere, sadat de twa draden tegearre kinne wurde draaid om ynterferinsje te ferminderjen.

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. De grutte fan induktive crosstalk hinget ôf fan ‘e tichtby fan’ e twa lussen, de grutte fan it lusgebiet, en de impedânsje fan ‘e beynfloede lading.

5. Stromkabelkoppeling: De AC- as DC -stroomkabels wurde bemuoie mei elektromagnetyske ynterferinsje

Oerdracht nei oare apparaten.

There are several ways to eliminate crosstalk in PCB design:

1. Beide soarten oerspraak ferheegje mei de tanimming fan loadimpedânsje, sadat de sinjaallinen gefoelich foar ynterferinsje feroarsake troch oerspraak moatte goed wurde beëinige.

2. Maksimalisearje de ôfstân tusken sinjaallinen om effektyf ferminderjen fan kapasitive crosstalk. Grûnbehear, ôfstân tusken bedrading (lykas aktive sinjaallinen en grûnlinen foar isolaasje, foaral yn ‘e steat sprong tusken de sinjaalline en grûn oant ynterval) en ferminderje leadinduktânsje.

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. Foar ferstannige oerspraak moat it lusgebiet minimalisearre wurde, en as tastien, moat de lus wurde elimineare.

5. Avoid signal sharing loops.

6. Jou omtinken oan sinjaalyntegriteit: de ûntwerper moat einen ymplementearje yn it lasproses om sinjaalyntegriteit op te lossen. Untwerpers dy’t dizze oanpak brûke, kinne har rjochtsje op ‘e mikrostriplange fan’ e ôfskermende koperfolie om goede prestaasjes fan sinjaalyntegriteit te krijen. 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. Lussen ferminderje: Elke lus is lyk oan in antenne, dus wy moatte it oantal lussen, it gebiet fan lussen en it antenne -effekt fan lussen minimalisearje. 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.

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Figuer 7: Filtertypen

3. The shielding. As gefolch fan ‘e lingte fan’ e kwestje plus in protte diskusje dy’t artikels beskermje, net mear spesifike ynlieding.

4. Reduce the speed of high-frequency devices.

5. Fergrutsje de dielektrike konstante fan PCB -boerd, dat kin foarkomme dat de dielen mei hege frekwinsje lykas transmissjeline by it boerd nei bûten útstrielje; 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. Foarsichtich beskôge bedrading en juste ôfslutings kinne fermogen ferminderje en induktive oerspraak.

4. Lûdûnderdrukking is fereaske om te foldwaan oan EMC -easken.