Katika muundo wa PCB bodi, pamoja na kuongezeka kwa kasi kwa masafa, kutakuwa na usumbufu mwingi ambao ni tofauti na ule wa bodi ya PCB yenye masafa ya chini. Kwa kuongezea, na kuongezeka kwa masafa na utata kati ya matumizi ya miniaturization na gharama ndogo ya bodi ya PCB, kuingiliwa huku kunazidi kuwa ngumu zaidi.

Katika utafiti halisi, tunaweza kuhitimisha kuwa kuna mambo manne ya usumbufu, pamoja na kelele ya usambazaji wa umeme, kuingiliwa kwa laini ya usambazaji, unganisha na kuingiliwa kwa umeme (EMI). Kupitia kuchambua shida anuwai za kuingiliwa kwa PCB yenye masafa mengi na kuchanganya na mazoezi katika kazi, suluhisho bora zinawekwa mbele.

Kwanza, kelele ya usambazaji wa umeme

Katika mzunguko wa mzunguko wa juu, kelele ya usambazaji wa umeme ina ushawishi dhahiri kwenye ishara ya masafa ya juu. Therefore, the first requirement of the power supply is low noise. Sakafu safi ni muhimu kama umeme safi. Kwa nini? Tabia za nguvu zinaonyeshwa kwenye Mchoro 1. Kwa wazi, usambazaji wa umeme una impedance fulani, na impedance inasambazwa juu ya usambazaji wote wa umeme, kwa hivyo, kelele itaongezwa kwa usambazaji wa umeme.

Then we should minimize the impedance of the power supply, so it is best to have a dedicated power supply layer and grounding layer. Katika muundo wa mzunguko wa hf, ni bora kubuni usambazaji wa umeme kama safu kuliko basi katika hali nyingi, ili kitanzi kiweze kufuata njia ya impedance ndogo.

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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Kielelezo 1: Tabia za nguvu

Kuna njia kadhaa za kuondoa kelele ya nguvu katika muundo wa 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. Ikiwa ufunguzi wa safu ya usambazaji wa umeme ni kubwa sana, lazima iathiri kitanzi cha ishara, ishara inalazimika kupita, eneo la kitanzi linaongezeka, na kelele huongezeka. At the same time, if several signal lines are clustered near the opening and share the same loop, the common impedance will cause crosstalk. Angalia Kielelezo 2.

Ubunifu wa PCB wa hali ya juu hutokea suluhisho za kuingiliwa

Kielelezo 2: Njia ya kawaida ya kitanzi cha ishara ya kupita

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 na umeme wa dijiti kutenganisha: vifaa vyenye masafa mengi kwa ujumla ni nyeti sana kwa kelele ya dijiti, kwa hivyo hizo mbili zinapaswa kutengwa, kuunganishwa pamoja kwenye mlango wa usambazaji wa umeme, ikiwa ishara kwenye sehemu za analog na dijiti za maneno, yanaweza kuwekwa kwenye ishara kwenye kitanzi ili kupunguza eneo la kitanzi. Urefu wa dijiti-analog uliotumiwa kwa kitanzi cha ishara unaonyeshwa kwenye Kielelezo 3.

Ubunifu wa PCB wa hali ya juu hutokea suluhisho za kuingiliwa

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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Kielelezo 4: Weka kamba ya umeme kando ya laini ya ishara

Two, transmission line

Kuna mistari miwili tu inayowezekana ya usambazaji katika PCB:

Shida kubwa ya laini ya Ribbon na laini ya microwave ni kutafakari. Tafakari itasababisha shida nyingi. Kwa mfano, ishara ya mzigo itakuwa nafasi ya ishara ya asili na ishara ya mwangwi, ambayo itaongeza ugumu wa uchambuzi wa ishara. Tafakari husababisha upotezaji wa kurudi (upotezaji wa kurudi), ambayo huathiri ishara vibaya kama kuingiliwa kwa kelele ya kuongeza:

1. Ishara iliyoonyeshwa nyuma kwa chanzo cha ishara itaongeza kelele za mfumo, na kuifanya iwe ngumu zaidi kwa mpokeaji kutofautisha kelele na ishara;

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) Epuka kukomeshwa kwa njia ya kutosababisha kasi ya njia za usafirishaji. Jambo la kukomesha kwa kukomesha ni hatua ya mabadiliko ya laini ya usambazaji, kama kona ya moja kwa moja, kupitia shimo, nk, inapaswa kuepukwa iwezekanavyo. Njia: Ili kuepuka pembe za moja kwa moja za mstari, kwa kadiri iwezekanavyo kwenda 45 ° Angle au arc, Angle kubwa pia inaweza kuwa; Tumia wachache kupitia mashimo iwezekanavyo, kwa sababu kila kupitia shimo ni kukomesha kwa impedance, kama inavyoonyeshwa kwenye 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. Kwa sababu laini yoyote ya rundo ni chanzo cha kelele. Ikiwa laini ya rundo ni fupi, inaweza kushikamana mwishoni mwa laini ya usambazaji; Ikiwa laini ya rundo ni ndefu, itachukua laini kuu ya usambazaji kama chanzo na kutoa tafakari kubwa, ambayo itasumbua shida. Inashauriwa usitumie.

Tatu, kuunganishwa

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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Kielelezo 6: Kuunganisha impedance ya kawaida

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. Kuunganisha huku kunapunguzwa sana, kwa hivyo waya hizo mbili zinaweza kusokotwa pamoja ili kupunguza kuingiliwa.

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. Ukubwa wa crosstalk ya kufata hutegemea ukaribu wa vitanzi viwili, saizi ya eneo la kitanzi, na impedance ya mzigo ulioathiriwa.

5. Kuunganisha kebo ya nguvu: nyaya za ac au DC zinaingiliwa na kuingiliwa kwa umeme

Hamisha kwa vifaa vingine.

There are several ways to eliminate crosstalk in PCB design:

1. Aina zote mbili za msalaba huongezeka na kuongezeka kwa impedance ya mzigo, kwa hivyo mistari ya ishara nyeti kwa usumbufu unaosababishwa na msalaba inapaswa kukomeshwa vizuri.

2. Ongeza umbali kati ya mistari ya ishara ili kupunguza ufanisi wa njia inayofaa. Usimamizi wa ardhi, nafasi kati ya wiring (kama vile mistari ya ishara inayotumika na mistari ya ardhini ya kutengwa, haswa katika hali ya kuruka kati ya laini ya ishara na ardhi hadi muda) na kupunguza inductance ya risasi.

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. Kwa msalaba wa busara, eneo la kitanzi linapaswa kupunguzwa, na ikiwa inaruhusiwa, kitanzi kinapaswa kuondolewa.

5. Avoid signal sharing loops.

6. Zingatia uadilifu wa ishara: mbuni anapaswa kutekeleza mwisho katika mchakato wa kulehemu ili kutatua uadilifu wa ishara. Wabunifu wanaotumia njia hii wanaweza kuzingatia urefu wa microstrip wa karatasi ya shaba iliyokinga ili kupata utendaji mzuri wa uadilifu wa ishara. 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. Punguza vitanzi: Kila kitanzi ni sawa na antena, kwa hivyo tunahitaji kupunguza idadi ya vitanzi, eneo la vitanzi na athari ya antena ya vitanzi. 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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Kielelezo 7: Aina za chujio

3. The shielding. Kama matokeo ya urefu wa toleo pamoja na nakala nyingi za majadiliano, hakuna utangulizi maalum.

4. Reduce the speed of high-frequency devices.

5. Ongeza dielectri ya bodi ya PCB, ambayo inaweza kuzuia sehemu za masafa ya juu kama vile laini ya usambazaji karibu na bodi kutoka nje; 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. Kuchunguza kwa uangalifu wiring na kukomesha sahihi kunaweza kupunguza njia inayofaa na inayoshawishi.

4. Ukandamizaji wa kelele unahitajika ili kukidhi mahitaji ya EMC.