A cikin zane na Kwamitin PCB, tare da saurin karuwar mitar, za a sami tsangwama da yawa wanda ya bambanta da na ƙaramar hukumar PCB. Bugu da ƙari, tare da ƙaruwa da mitar da sabani tsakanin ƙaramin aiki da ƙaramin farashi na hukumar PCB, waɗannan tsangwama za su ƙara yin rikitarwa.

A cikin ainihin bincike, za mu iya kammala cewa galibin fuskoki guda huɗu na tsangwama, gami da hayaniyar samar da wutar lantarki, tsoma bakin layin watsawa, haɗin gwiwa da kutse na lantarki (EMI). Ta hanyar nazarin matsaloli daban-daban na tsangwama na PCB mai yawan mita da haɗawa tare da aiki a cikin aiki, ana gabatar da ingantattun mafita.

Na farko, hayaniyar wutar lantarki

A cikin madaidaicin madaidaicin mita, amo na samar da wutar lantarki yana da tasiri a bayyane akan siginar mitar. Therefore, the first requirement of the power supply is low noise. Tsabtattun benaye suna da mahimmanci kamar tsaftataccen wutar lantarki. Me ya sa? Ana nuna halayen ikon a cikin hoto 1. A bayyane yake, wutar lantarki tana da takamaiman abin hanawa, kuma an rarraba matsalar a kan duk wutar lantarki, saboda haka, za a ƙara hayaniya zuwa wutar lantarki.

Then we should minimize the impedance of the power supply, so it is best to have a dedicated power supply layer and grounding layer. A cikin ƙirar kewaye na hf, yana da kyau ƙira don samar da wutar lantarki azaman Layer fiye da bas a mafi yawan lokuta, don madauki koyaushe zai iya bin tafarkin ƙarancin ƙarancin ƙarfi.

Bugu da ƙari, hukumar wutar lantarki dole ne ta samar da madaidaicin siginar siginar siginar don duk abubuwan da aka samar kuma aka karɓa akan PCB. Wannan yana rage madaidaicin siginar kuma ta haka yana rage amo, wanda galibi masu ƙirar kewaya kewaye ke yin watsi da shi.

Babban ƙirar PCB mai yawa yana faruwa mafita mafita

Hoto 1: Halayen wutar lantarki

Akwai hanyoyi da yawa don kawar da amo a cikin ƙirar 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. Idan buɗe Layer na samar da wutar lantarki ya yi yawa, an daure ya shafi madaurin siginar, ana tilasta siginar ta wuce, yankin madauki yana ƙaruwa, kuma amo yana ƙaruwa. At the same time, if several signal lines are clustered near the opening and share the same loop, the common impedance will cause crosstalk. Duba Hoto na 2.

Babban ƙirar PCB mai yawa yana faruwa mafita mafita

Hoto 2: Hanyar gama gari na madaidaicin siginar kewaya

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 da wutar lantarki na dijital don rarrabewa: na’urori masu yawan mita gabaɗaya suna da matuƙar damuwa ga amo na dijital, don haka yakamata a raba su biyu, a haɗa su gaba ɗaya a ƙofar wutan lantarki, idan siginar ta ƙetare analog da sassan dijital na kalmomi, za a iya sanya su cikin siginar a fadin madauki don rage yankin madauki. An nuna tsayin dijital-analog da aka yi amfani da shi don madaurin siginar a cikin Hoto 3.

Babban ƙirar PCB mai yawa yana faruwa mafita mafita

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.

Babban ƙirar PCB mai yawa yana faruwa mafita mafita

Hoto 4: Sanya igiyar wutan a gefen layin siginar

Two, transmission line

Akwai layukan watsawa guda biyu kawai a cikin PCB:

Babbar matsalar layin kintinkiri da layin microwave shine tunani. Tunani zai haifar da matsaloli da yawa. Misali, siginar kaya za ta kasance mafi girman siginar asali da siginar amsa kuwwa, wanda zai kara wahalar nazarin siginar. Tunani yana haifar da asarar dawowa (asarar koma baya), wanda ke shafar siginar azaman mugun tsangwama na amo:

1. Siginar da aka yi nuni da ita zuwa tushen siginar zai ƙara hayaniyar tsarin, yana mai wahalar da mai karɓa don rarrabe amo daga sigina;

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) Gujewa hana katse hanyoyin watsawa. Ma’anar dakatarwar da ba ta ƙare ba ita ce ma’anar maye gurbin layin watsawa, kamar kusurwa madaidaiciya, ta rami, da sauransu, ya kamata a guji shi gwargwadon iko. Hanyoyi: Don gujewa madaidaiciyar kusurwoyin layi, gwargwadon yiwuwar zuwa 45 ° Angle ko arc, babban Angle na iya kasancewa; Yi amfani da kaɗan ta cikin ramuka yadda zai yiwu, saboda kowane ta cikin rami shine katsewar rashin ƙarfi, kamar yadda aka nuna a FIG. 5; Signals from the outer layer avoid passing through the inner layer and vice versa.

Babban ƙirar PCB mai yawa yana faruwa mafita mafita

Figure 5: Method for eliminating transmission line interference

(b) Do not use stake lines. Domin duk wani layin tari yana haifar da hayaniya. Idan layin tari ya takaice, ana iya haɗa shi a ƙarshen layin watsawa; Idan layin tari ya yi tsawo, zai ɗauki babban layin watsawa a matsayin tushen kuma ya samar da babban tunani, wanda zai wahalar da matsalar. Ana ba da shawarar kada a yi amfani da shi.

Na uku, hadawa

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.

Babban ƙirar PCB mai yawa yana faruwa mafita mafita

Hoto na 6: Haɗin haɗarin gama gari

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. Wannan haɗin yana raguwa sosai, don haka za a iya murɗa wayoyin biyu tare don rage tsangwama.

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. Girman crosstalk inductive ya dogara da kusancin madaukai biyu, girman yanki na madauki, da kuma hanawar nauyin da abin ya shafa.

5. Haɗin kebul na wutar lantarki: Ana yin kutse da igiyoyin wutar AC ko DC ta hanyar kutse na lantarki

Canja wurin wasu na’urori.

There are several ways to eliminate crosstalk in PCB design:

1. Duka iri -iri na ƙaruwa suna ƙaruwa tare da ƙaruwa na rashin ƙarfi, don haka layin siginar da ke kula da tsangwama da crosstalk ya haifar ya kamata a ƙare da kyau.

2. Ƙara tazara tsakanin layin siginar don rage yadda ake amfani da ƙwanƙwasa. Gudanar da ƙasa, tazara tsakanin wayoyi (kamar layin siginar aiki da layin ƙasa don keɓewa, musamman a cikin yanayin tsalle tsakanin layin siginar da ƙasa zuwa tazara) da rage shigar gubar.

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. Don tsattsauran ra’ayi mai hankali, yakamata a rage yankin madauki, kuma idan an yarda, yakamata a kawar da madauki.

5. Avoid signal sharing loops.

6. Kula da amincin sigina: yakamata mai zanen ya aiwatar da ƙarewa a cikin tsarin walda don warware amincin sigina. Masu zanen kaya da ke amfani da wannan hanyar za su iya mai da hankali kan tsayin microstrip na farantin ƙarfe na garkuwa don samun kyakkyawan aiki na mutuncin sigina. 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.

Akwai hanyoyi da yawa don kawar da tsangwama na lantarki a cikin ƙirar PCB:

1. Rage madaukai: Kowane madauki daidai yake da eriya, don haka muna buƙatar rage yawan madaukai, yankin madaukai da tasirin eriya na madaukai. 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.

Babban ƙirar PCB mai yawa yana faruwa mafita mafita

Hoto 7: Nau’o’in tacewa

3. The shielding. Sakamakon tsawon batun tare da tattaunawa mai yawa na kare labaran, babu takamaiman gabatarwa.

4. Reduce the speed of high-frequency devices.

5. Ƙara madaidaiciyar madaidaiciyar allon PCB, wanda zai iya hana manyan sassan mitar kamar layin watsawa kusa da jirgin daga haskakawa waje; 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. Anyi la’akari da wayoyi masu kyau da ƙarewar da ta dace na iya kawar da tunani.

3. Anyi la’akari da wayoyi masu kyau da ƙarewar da ta dace na iya rage ƙarfin jujjuyawar ƙarfe.

4. Ana buƙatar murƙushe hayaniya don biyan buƙatun EMC.