Nan desen an nan Komisyon Konsèy PCB, Avèk ogmantasyon rapid nan frekans, pral gen yon anpil nan entèferans ki diferan de sa ki nan tablo ki ba-frekans PCB. Anplis, ak ogmantasyon nan frekans ak kontradiksyon ki genyen ant miniaturizasyon a ak pri ki ba nan tablo PCB, entèferans sa yo ap vin pi plis ak plis konplike.

Nan rechèch aktyèl la, nou ka konkli ke gen sitou kat aspè nan entèferans, ki gen ladan bri ekipman pou pouvwa, entèferans liy transmisyon, kouti ak entèferans elektwomayetik (EMI). Atravè analize pwoblèm entèferans divès kalite PCB segondè-frekans ak konbine avèk pratik nan travay, solisyon efikas yo mete devan.

Premyèman, bri ekipman pou pouvwa

Nan kous la frekans segondè, bri a nan ekipman pou pouvwa gen yon enfliyans evidan sou siyal la frekans segondè. Therefore, the first requirement of the power supply is low noise. Planche pwòp yo enpòtan menm jan ak elektrisite pwòp. Poukisa? Karakteristik pouvwa yo montre nan Figi 1. Li evidan, ekipman pou pouvwa a gen yon enpedans sèten, ak enpedans la distribye sou ekipman pou pouvwa a tout antye, Se poutèt sa, yo pral bri a dwe ajoute nan ekipman pou pouvwa a.

Then we should minimize the impedance of the power supply, so it is best to have a dedicated power supply layer and grounding layer. Nan konsepsyon sikwi hf, li pi bon pou konsepsyon ekipman pou pouvwa a kòm yon kouch pase kòm yon otobis nan pifò ka yo, se konsa ke bouk la ka toujou swiv chemen an nan enpedans minim.

Anplis de sa, tablo a pouvwa dwe bay yon bouk siyal pou tout pwodwi ak resevwa siyal sou PCB la. Sa a minimize bouk la siyal e konsa diminye bri, ki se souvan neglije pa ba-frekans konsèpteur sikwi.

High-frekans PCB konsepsyon rive solisyon entèferans

Figi 1: Karakteristik pouvwa

Gen plizyè fason pou elimine bri pouvwa nan konsepsyon PCB:

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. Si ouvèti kouch ekipman pou pouvwa a twò gwo, li mare pou afekte bouk siyal la, siyal la fòse kontoune, zòn bouk la ogmante, epi bri a ogmante. At the same time, if several signal lines are clustered near the opening and share the same loop, the common impedance will cause crosstalk. Al gade nan Figi 2.

High-frekans PCB konsepsyon rive solisyon entèferans

Figi 2: Chemen komen nan bouk siyal kontoune

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. Analog ak dijital ekipman pou pouvwa a separe: aparèy wo-frekans yo jeneralman trè sansib a bri dijital, se konsa de la ta dwe separe, konekte ansanm nan papòt la nan ekipman pou pouvwa a, si siyal la atravè pati yo analòg ak dijital nan la mo, yo ka mete yo nan siyal la atravè yon bouk diminye zòn nan bouk. Span nan dijital-analòg yo itilize pou bouk la siyal yo montre nan Figi 3.

High-frekans PCB konsepsyon rive solisyon entèferans

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.

High-frekans PCB konsepsyon rive solisyon entèferans

Figi 4: Mete kòd pouvwa a bò liy siyal la

Two, transmission line

Gen sèlman de liy transmisyon posib nan yon PCB:

Pwoblèm nan pi gwo nan liy riban ak liy mikwo ond se refleksyon. Refleksyon ap lakòz anpil pwoblèm. Pou egzanp, siyal la chaj yo pral supèrpozisyon nan siyal orijinal la ak siyal la eko, ki pral ogmante difikilte pou yo nan analiz siyal. Refleksyon lakòz pèt retou (pèt retou), ki afekte siyal la tankou seryezman tankou entèferans bri aditif:

1. Siyal la reflete tounen nan sous la siyal ap ogmante bri a nan sistèm lan, ki fè li pi difisil pou reseptè a yo fè distenksyon ant bri soti nan siyal;

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) Evite enkonvenyans enpedans nan liy transmisyon yo. Pwen nan enpedans discontinuous se pwen nan liy mitasyon transmisyon, tankou kwen dwat, nan twou, elatriye, yo ta dwe evite osi lwen ke posib. Metòd: Pou evite kwen dwat nan liy lan, osi lwen ke posib yo ale 45 ° Ang oswa arc, gwo Ang kapab tou; Sèvi ak kèk nan twou ke posib, paske chak nan twou se yon enkonvenyans enpedans, jan yo montre nan FIG. 5; Signals from the outer layer avoid passing through the inner layer and vice versa.

High-frekans PCB konsepsyon rive solisyon entèferans

Figure 5: Method for eliminating transmission line interference

(b) Do not use stake lines. Paske nenpòt liy pil se yon sous bri. Si liy lan pil se kout, li ka konekte nan fen liy lan transmisyon; Si liy lan pil long, li pral pran liy lan transmisyon prensipal kòm sous la ak pwodwi gwo refleksyon, ki pral konplike pwoblèm nan. Li rekòmande pou pa sèvi ak li.

Twazyèmman, kouti a

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.

High-frekans PCB konsepsyon rive solisyon entèferans

Figi 6: Kouple enpedans komen

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. Sa a se kouple anpil redwi, se konsa de fil yo ka trese ansanm diminye entèferans.

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. Gwosè a nan kwazman endiktif depann sou pwoksimite a nan de pasan yo, gwosè a nan zòn nan bouk, ak enpedans nan chaj la ki afekte yo.

5. Pouvwa kab kouple: câbles yo AC oswa DC pouvwa yo entèfere pa entèferans elektwomayetik

Transfere nan lòt aparèy.

There are several ways to eliminate crosstalk in PCB design:

1. Tou de kalite krosstalk ogmante ak ogmantasyon nan enpedans chaj, se konsa liy yo siyal sansib a entèferans ki te koze pa krosstalk yo ta dwe byen sispann.

2. Maksimize distans ki genyen ant liy siyal yo pou efektivman diminye kapasitif kapasitif. Jesyon tè, espas ant fil elektrik (tankou liy siyal aktif ak liy tè pou izolasyon, espesyalman nan eta so ant liy siyal la ak tè a entèval) epi redwi enduktans plon.

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. Pou kwasans sansib, yo ta dwe minimize zòn bouk la, epi si yo pèmèt li, yo ta dwe elimine bouk la.

5. Avoid signal sharing loops.

6. Peye atansyon sou entegrite siyal: designer a ta dwe aplike bout nan pwosesis la soude yo rezoud entegrite siyal. Konsèpteur lè l sèvi avèk apwòch sa a ka konsantre sou longè a mikrostrip nan fèy la kòb kwiv mete pwoteksyon yo nan lòd yo jwenn bon pèfòmans nan entegrite siyal. 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.

Gen plizyè fason pou elimine entèferans elektwomayetik nan konsepsyon PCB:

1. Diminye pasan: Chak riban ekivalan a yon antèn, kidonk nou bezwen minimize kantite pasan, zòn pasan ak efè antèn pasan. 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.

High-frekans PCB konsepsyon rive solisyon entèferans

Figi 7: Kalite filtre

3. The shielding. Kòm yon rezilta nan longè a nan pwoblèm nan plis yon anpil nan diskisyon pwoteje atik, pa gen okenn entwodiksyon espesifik ankò.

4. Reduce the speed of high-frequency devices.

5. Ogmante konstan Dielectric nan tablo PCB, sa ki ka anpeche pati frekans segondè yo tankou liy transmisyon tou pre tablo a soti nan gaye deyò; 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. Ak anpil atansyon konsidere fil elektrik ak revokasyon apwopriye ka elimine refleksyon.

3. Ak anpil atansyon konsidere fil elektrik ak revokasyon apwopriye ka diminye kapasitif ak enduktiv kwazman.

4. Se repwesyon bri oblije satisfè kondisyon EMC.