Zininzi iindlela zokusombulula iingxaki ze-EMI. Iindlela zale mihla zocinezelo ze-EMI ziquka: ukusebenzisa i-EMI yocinezelo yokwaleka, ukukhetha iindawo ezifanelekileyo zokucinezelwa kwe-EMI, kunye noyilo lokulinganisa lwe-EMI. Ukuqala kweyona nto isisiseko PCB Ubeko, eli nqaku lixoxa ngendima kunye neendlela zoyilo lwe-PCB enemaleko ebekwe ekulawuleni radiation ye-EMI.

Ukubeka ngokufanelekileyo ii-capacitors zomthamo ofanelekileyo kufutshane nezikhonkwane zobonelelo lwamandla ze-IC kunokwenza i-IC output voltage itsibe ngokukhawuleza. Nangona kunjalo, ingxaki ayipheli apha. Ngenxa yokuphendula okulinganiselweyo kwee-frequency capacitors, oku kwenza ukuba ii-capacitors zingakwazi ukuvelisa amandla e-harmonic afunekayo ukuqhuba ukukhutshwa kwe-IC ngokucocekileyo kwi-band frequency band. Ukongeza, i-voltage yexeshana eyenziwe kwibha yebhasi yamandla iya kwenza ukuhla kwamandla ombane kwi-inductor yendlela yokuqhawula. La mandla ombane adlulayo zezona mithombo ziphambili zophazamiseko ze-EMI. Sifanele sizisombulule njani ezi ngxaki?

Ngokubhekiselele kwi-IC kwibhodi yethu yesiphaluka, umbane wamandla ojikeleze i-IC unokuthathwa njenge-capacitor ephezulu-frequency capacitor, enokuqokelela inxalenye yamandla avuzayo yi-discrete capacitor enika amandla aphezulu-frequency ukucoca. imveliso. Ukongeza, i-inductance yomgangatho ofanelekileyo wamandla kufuneka ibe yincinci, ngoko ke isiginali yethutyana edityaniswe yi-inductance nayo incinci, ngaloo ndlela inciphisa imo ye-EMI eqhelekileyo.

Ngokuqinisekileyo, uxhulumaniso phakathi koluhlu lwamandla kunye nepini yamandla e-IC kufuneka ibe mfutshane ngokusemandleni, kuba umgca wokunyuka wesignali yedijithali ukhawuleza kwaye ukhawuleza, kwaye kungcono ukuyidibanisa ngokuthe ngqo kwi-pad apho amandla e-IC. iphini ikhona. Oku kufuneka kuxoxwe ngokwahlukeneyo.

Ukuze ulawule i-EMI yendlela eqhelekileyo, inqwelomoya yombane kufuneka incede ukuqhawuka kwaye ibe ne-inductance ephantsi ngokwaneleyo. Le nqwelo-moya yamandla kufuneka ibe yinqwelo-moya eyilwe kakuhle. Omnye unokubuza, ukuba kuhle kangakanani? Impendulo yombuzo ixhomekeke ekubekweni kwamandla ombane, izixhobo phakathi kwemigangatho, kunye ne-frequency yokusebenza (oko kukuthi, umsebenzi wokunyuka kwexesha le-IC). Ngokubanzi, isithuba somaleko wamandla yi-6mil, kunye ne-interlayer yi-FR4 impahla, i-capacitance elinganayo yomaleko wamandla nge-intshi nganye yesikwere malunga ne-75pF. Ngokucacileyo, okukhona kuncinci izithuba zomaleko, kokukhona isithuba esikhulu.

Akukho zixhobo ezininzi ezinexesha lokunyuka kwe-100 ukuya kwi-300 ps, ​​kodwa ngokwesantya sophuhliso lwe-IC yangoku, izixhobo ezinexesha lokunyuka kuluhlu lwe-100 ukuya kwi-300 ps ziya kuthatha indawo ephezulu. Kwiisekethe ezinexesha lokunyuka kwe-100 ukuya kwi-300ps, izithuba ze-3mil ze-layer aziyi kuba zilungele izicelo ezininzi. Ngelo xesha, kwakuyimfuneko ukusebenzisa itekhnoloji yokubeka i-layer spacing engaphantsi kwe-1 mil, kunye nokutshintsha izinto ze-dielectric ze-FR4 kunye nezixhobo ezine-dielectric constants. Ngoku, ii-ceramics kunye neeplastiki ze-ceramic zinokuhlangabezana neemfuno zoyilo lwe-100 ukuya kwi-300 ps iisekhethi zexesha lokunyuka.

Nangona izixhobo ezintsha kunye neendlela ezintsha zinokusetyenziswa kwixesha elizayo, kwi-1 ukuya kwi-3ns yexesha lokunyuka kweesekethe, i-3 ukuya kwi-6mil yokubeka isithuba kunye nezixhobo ze-dielectric ze-FR4, ngokuqhelekileyo kwanele ukusingatha i-harmonics ephezulu kunye nokwenza umqondiso wexeshana ube phantsi ngokwaneleyo. , oko kukuthi, Imowudi eqhelekileyo EMI inokuncitshiswa kakhulu. Imizekelo yoyilo olucwangcisiweyo lwe-PCB enikwe kweli nqaku iya kuthatha isithuba somaleko se-3 ukuya kwi-6 mils.

Ukhuselo lombane

Ngokombono weempawu zomkhondo, isicwangciso esilungileyo sokubeka isicwangciso kufuneka sibe kukubeka zonke iimpawu zesignali kuluhlu olunye okanye ngaphezulu, ezi zingqimba zisecaleni komgangatho wamandla okanye umgangatho womhlaba. Kunikezelo lwamandla, isicwangciso esilungileyo sokubeka i-maleko kufuneka sibe ukuba umaleko wamandla usondele kumaleko omhlaba, kwaye umgama phakathi komgangatho wamandla kunye nomgangatho womhlaba uncinci kangangoko. Yile nto esiyibiza ngokuba sisicwangciso “sokwendlalela”.

Ukupakishwa kwePCB

Loluphi uhlobo lwesicwangciso sokupakisha esinokunceda ukukhusela kunye nokucinezela i-EMI? Isikimu sokupakisha esinemaleko esilandelayo sithatha ukuba umbane okhoyo uqukuqela kwinqanaba elinye, kwaye i-voltage enye okanye ii-voltages ezininzi zisasazwa kwiindawo ezahlukeneyo zomaleko ofanayo. Imeko yomaleko wamandla amaninzi iya kuxoxwa kamva.

Ibhodi ye-4-layer

Kukho iingxaki ezininzi ezinokubakho ngoyilo lwebhodi ye-4-layer. Okokuqala, ibhodi yemveli ezine umaleko kunye ubukhulu 62 mils, nokuba umaleko uphawu phezu umaleko olungaphandle, kwaye amandla kunye namaleko komhlaba phezu umaleko wangaphakathi, umgama phakathi umaleko amandla kunye umaleko komhlaba. isenkulu kakhulu.

Ukuba imfuno yeendleko yeyokuqala, unokuqwalasela ezi ndlela zimbini zilandelayo kwibhodi yendabuko ye-4. Ezi zisombululo zibini zinokuphucula ukusebenza koxinzelelo lwe-EMI, kodwa zifanelekile kuphela kwizicelo apho ukuxinana kwecandelo ebhodini kuphantsi ngokwaneleyo kwaye kukho indawo eyaneleyo ejikeleze amacandelo (beka umbane wobhedu ofunekayo).

Ukhetho lokuqala lukhetho lokuqala. Iimaleko zangaphandle zePCB zizo zonke iileya zomhlaba, kwaye imigangatho emibini ephakathi yimiqondiso/izaleko zamandla. Unikezelo lwamandla kuluhlu lwesignali luhanjiswa ngomgca obanzi, onokuthi wenze i-impedance yendlela yokunikezelwa kwamandla ngoku iphantsi, kwaye i-impedance yendlela yesignali ye-microstrip nayo iphantsi. Ukusuka kwimbono yolawulo lwe-EMI, le lolona luhlu luhle lwe-PCB ye-4-layer ekhoyo. Kwiskimu sesibini, umaleko wangaphandle usebenzisa amandla kunye nomhlaba, kwaye imigangatho emibini ephakathi isebenzisa izibonakaliso. Xa kuthelekiswa nebhodi yendabuko ye-4-layer, ukuphuculwa kuncinci, kwaye i-impedance ye-interlayer imbi njengebhodi yendabuko ye-4.

Ukuba ufuna ukulawula i-impedance trace, iskimu sokupakisha esingentla kufuneka silumke kakhulu ukulungelelanisa imikhondo phantsi kwamandla kunye neziqithi zethusi zomhlaba. Ukongezelela, iziqithi zethusi kumandla ombane okanye umgangatho womhlaba kufuneka zixhunywe ngokusemandleni ukuqinisekisa ukuba i-DC kunye ne-low-frequency connectivity.

Ibhodi ye-6-layer

Ukuba ubuninzi bamacandelo kwibhodi ye-4-layer iphezulu, ibhodi ye-6-layer iyona nto ingcono. Nangona kunjalo, ezinye izikimu zokupakisha kuyilo lwebhodi ye-6 azilungile ngokwaneleyo ukukhusela intsimi ye-electromagnetic, kwaye zinefuthe elincinci ekunciphiseni umqondiso wexeshana webhasi yamandla. Imizekelo emibini ixoxwa apha ngezantsi.

Kwimeko yokuqala, ukunikezelwa kwamandla kunye nomhlaba kubekwe kwinqanaba le-2 kunye ne-5 ngokulandelanayo. Ngenxa ye-impedance ephezulu yokugquma kobhedu kunikezelo lwamandla, akulunganga kakhulu ukulawula imo yemitha ye-EMI eqhelekileyo. Nangona kunjalo, ukusuka kwindawo yokujonga ulawulo lwe-impedance yesignali, le ndlela ichanekile kakhulu.