Ngenxa yobukhulu nosayizi omncane, cishe awekho amazinga ebhodi lesifunda aphrintiwe emakethe ekhulayo ye-IoT egqokekayo. Ngaphambi kokuthi kuphume la mazinga, bekufanele sithembele olwazini nasekuzikhiqizeni okufundwe ekuthuthukisweni kwezinga lebhodi futhi sicabange ukuthi singazisebenzisa kanjani ezinseleleni ezihlukile ezivelayo. Kunezindawo ezintathu ezidinga ukunakekelwa kwethu okukhethekile. Yilawa: izinto zebhodi lesifunda, idizayini ye-RF/microwave kanye nemigqa yokudlulisa ye-RF.

PCB impahla

I-“PCB” ngokuvamile iqukethe ama-laminates, angase enziwe nge-fiber-reinforced epoxy (FR4), i-polyimide noma izinto ze-Rogers noma ezinye izinto zokwakha. I-insulating material phakathi kwezingqimba ezihlukene ibizwa ngokuthi i-prepreg.

amadivayisi agqokekayo adinga ukwethembeka okuphezulu, ngakho-ke lapho abaklami be-PCB bebhekene nokukhetha ukusebenzisa i-FR4 (impahla yokukhiqiza ye-PCB engabizi kakhulu) noma izinto ezithuthuke kakhulu nezimba eqolo, lokhu kuzoba inkinga.

Uma izinhlelo zokusebenza ze-PCB ezigqokekayo zidinga izinto ezisetshenziswayo ezinesivinini esikhulu, imvamisa ephezulu, i-FR4 ingase ingabi inketho engcono kakhulu. I-dielectric constant (Dk) ye-FR4 yi-4.5, i-dielectric constant ye-Rogers 4003 series material ethuthuke kakhulu ingu-3.55, kanye ne-dielectric constant yochungechunge lwabazalwane uRogers 4350 ngu-3.66.

“I-dielectric constant ye-laminate ibhekisela esilinganisweni somthamo noma amandla phakathi kwamakhondatha amabili eduze kwe-laminate kuya ku-capacitance noma amandla phakathi kwamakhondatha amabili ku-vacuum. Emazingeni aphezulu, kungcono ukulahlekelwa okuncane. Ngakho-ke, i-Roger 4350 ene-dielectric constant engu-3.66 ifaneleka kakhulu kuzicelo zefrikhwensi ephezulu kune-FR4 ene-dielectric constant engu-4.5.

Ngaphansi kwezimo ezijwayelekile, inani lezendlalelo ze-PCB zamadivayisi agqokekayo lisukela kwezingu-4 kuye kweziyi-8. Isimiso sokwakhiwa kwesendlalelo siwukuthi uma i-PCB enezingqimba ezingu-8, kufanele ikwazi ukunikeza izendlalelo ezanele zomhlaba kanye namandla kanye nesemishi ungqimba lwezintambo. Ngale ndlela, umphumela we-ripple ku-crosstalk ungagcinwa usezingeni eliphansi futhi ukuphazamiseka kwe-electromagnetic (EMI) kungancishiswa kakhulu.

Esigabeni sokuklama isakhiwo sebhodi lesifunda, uhlelo lokuhlela ngokuvamile lubeka ungqimba olukhulu lomhlabathi eduze kwesendlalelo sokusabalalisa amandla. Lokhu kungakha umphumela we-ripple ophansi kakhulu, futhi umsindo wesistimu ungancishiswa cishe ucishe uziro. Lokhu kubaluleke kakhulu ohlelweni olungaphansi lwefrikhwensi yomsakazo.

Uma kuqhathaniswa nempahla ye-Rogers, i-FR4 inesici esiphezulu sokulahla (i-Df), ikakhulukazi emazingeni aphezulu. Ngokusebenza okuphezulu kwama-laminates e-FR4, inani le-Df lilinganiselwa ku-0.002, okuwuhlelo lobukhulu olungcono kune-FR4 evamile. Nokho, isitaki sikaRogers singu-0.001 kuphela noma ngaphansi. Uma into ye-FR4 isetshenziselwa izinhlelo zokusebenza zemvamisa ephezulu, kuzoba nomehluko omkhulu ekulahlekeni kokufakwa. Ukulahlekelwa kokufaka kuchazwa njengokulahlekelwa amandla esiginali ukusuka endaweni A ukuya endaweni B lapho usebenzisa i-FR4, Rogers noma ezinye izinto.

dala izinkinga

I-PCB egqokekayo idinga ukulawula okuqinile. Lokhu kuyisici esibalulekile samadivayisi agqokekayo. Ukufaniswa kwe-Impedans kungaveza ukudluliswa kwesignali okuhlanzekile. Ngaphambilini, ukubekezelela okujwayelekile kokulandela umkhondo wokuphatha amasignali kwakungu ±10%. Le nkomba ngokusobala ayilungile ngokwanele kumasekhethi anamuhla anemvamisa ephezulu kanye nesivinini esikhulu. Isidingo samanje singu-±7%, futhi kwezinye izimo ngisho no-±5% noma ngaphansi. Le pharamitha nokunye okuguquguqukayo kuzothinta kabi ukwenziwa kwalawa ma-PCB agqokekayo anokulawula okuqinile ikakhulukazi kokuvimbela, ngaleyo ndlela kunciphise inani lamabhizinisi angawakhiqiza.

Ukubekezelela njalo kwe-dielectric kwe-laminate eyenziwe ngezinto ze-Rogers UHF ngokuvamile kugcinwa ku-±2%, futhi eminye imikhiqizo ingafinyelela ku-±1%. Ngokuphambene, ukubekezelelana kwe-dielectric njalo kwe-FR4 laminate kuphezulu njengo-10%. Ngakho-ke, qhathanisa Lezi zinto ezimbili zingatholakala ukuthi ukulahlekelwa kokufaka kukaRogers kuphansi kakhulu. Uma kuqhathaniswa nezinto ezivamile ze-FR4, ukulahleka kokudlulisela nokulahlekelwa kokufakwa kwesitaki se-Rogers kuphansi ngohhafu.

Ezimweni eziningi, izindleko zibaluleke kakhulu. Kodwa-ke, ama-Rogers anganikeza ukulahlekelwa okuphansi kokusebenza kwe-laminate ephezulu endaweni yephuzu lentengo elamukelekayo. Kuzinhlelo zokusebenza zentengiso, ama-Rogers angenziwa i-PCB eyingxube ene-epoxy-based FR4, ezinye izendlalelo ezisebenzisa impahla ye-Rogers, kanti ezinye izendlalelo zisebenzisa i-FR4.

Lapho ukhetha isitaki sikaRogers, imvamisa iwukucatshangelwa okuyinhloko. Lapho imvamisa idlula u-500MHz, abaklami be-PCB bavame ukukhetha izinto ze-Rogers, ikakhulukazi amasekhethi e-RF/microwave, ngoba lezi zinto zinganikeza ukusebenza okuphezulu lapho iminonjana engaphezulu ilawulwa ngokuqinile yi-impedance.

Uma kuqhathaniswa nempahla ye-FR4, impahla ye-Rogers nayo inganikeza ukulahleka kwe-dielectric ephansi, futhi i-dielectric njalo yayo izinzile ebangeni elibanzi. Ngaphezu kwalokho, izinto ze-Rogers zinganikeza ukusebenza okuphansi kokulahlekelwa kokufakwa okudingekayo ngokusebenza kwemvamisa ephezulu.

I-coefficient of thermal expansion (CTE) yezinto zochungechunge ze-Rogers 4000 inokuqina okuhle kakhulu kobukhulu. Lokhu kusho ukuthi uma kuqhathaniswa ne-FR4, lapho i-PCB idlula imijikelezo yokudambisa ebandayo, eshisayo futhi eshisa kakhulu, ukunwetshwa okushisayo nokufinyezwa kwebhodi lesifunda kungagcinwa emkhawulweni ozinzile ngaphansi kwemvamisa ephezulu kanye nemijikelezo yokushisa ephezulu.

Endabeni yokunqwabelanisa okuxubile, kulula ukusebenzisa ubuchwepheshe benqubo yokukhiqiza evamile ukuxuba ama-Rogers kanye ne-FR4 esebenza kahle kakhulu ndawonye, ​​ngakho kulula ukuzuza isivuno esikhulu sokukhiqiza. Isitaki sikaRogers asidingi okukhethekile ngenqubo yokulungiselela.

I-FR4 evamile ayikwazi ukuzuza ukusebenza kukagesi okuthembeke kakhulu, kodwa izinto ezisebenza kahle ze-FR4 zinezici ezinhle zokwethembeka, njenge-Tg ephakeme, ezisabiza kancane uma kuqhathaniswa, futhi zingasetshenziswa ezinhlobonhlobo zezinhlelo zokusebenza, kusukela ekwakhiweni komsindo olula kuye kuzinhlelo zokusebenza ze-microwave eziyinkimbinkimbi. .

Ukucatshangelwa kwe-RF/Microwave design

Ubuchwepheshe obuphathekayo kanye ne-Bluetooth kuvule indlela yezinhlelo zokusebenza ze-RF/microwave kumadivayisi agqokekayo. Ibanga lefrikhwensi lanamuhla liya ngokuya liguquka. Eminyakeni embalwa edlule, imvamisa ephezulu kakhulu (VHF) yayichazwa njenge-2GHz~3GHz. Kepha manje singabona izinhlelo zokusebenza ze-Ultra-high frequency (UHF) ezisukela ku-10GHz ziye ku-25GHz.

Ngakho-ke, ku-PCB egqokekayo, ingxenye ye-RF idinga ukunakwa okwengeziwe ezindabeni zezintambo, futhi amasignali kufanele ahlukaniswe ngokwehlukana, futhi iminonjana ekhiqiza amasignali amaza aphezulu kufanele igcinwe kude nomhlaba. Okunye okucatshangelwayo kufaka phakathi: ukuhlinzeka ngesihlungi se-bypass, ama-capacitor e-decoupling anele, ukubeka phansi, nokuklama ulayini wokudlulisela kanye nolayini wokubuya ukuze ucishe ulingane.

Isihlungi se-Bypass singacindezela umphumela we-ripple wokuqukethwe komsindo ne-crosstalk. Ama-Decoupling capacitor adinga ukubekwa eduze nezikhonkwane zedivayisi eziphethe amasignali amandla.

Imigqa yokudlulisela enesivinini esikhulu namasekhethi esignali adinga ungqimba oluphansi oluzobekwa phakathi kwamasignali ongqimba lwamandla ukuze bushelelezi i-jitter ekhiqizwa amasignali omsindo. Ngezivinini eziphakeme zesignali, ukungafani okuncane kwe-impedance kuzodala ukudluliswa okungalingani nokwamukela amasignali, okuholela ekuhlanekeni. Ngakho-ke, ukunakekelwa okukhethekile kufanele kukhokhwe enkingeni yokufanisa i-impedance ehlobene nesignali yefrikhwensi yomsakazo, ngoba isignali yefrikhwensi yomsakazo inesivinini esikhulu nokubekezelelana okukhethekile.

Izintambo zokudlulisa i-RF zidinga ukuthintana okulawulwayo ukuze kudluliselwe amasiginali e-RF kusuka ku-IC substrate ethile kuya ku-PCB. Le migqa yokudlulisela ingasetshenziswa kungqimba olungaphandle, ungqimba olungaphezulu, nolwendlalelo olungezansi, noma lungaklanywa kungqimba oluphakathi.

Izindlela ezisetshenziswa ngesikhathi sokuklanywa kwe-PCB RF ulayini we-microstrip, umugqa we-strip ontantayo, i-coplanar waveguide noma isisekelo. Umugqa we-microstrip uqukethe ubude obunqunyiwe bensimbi noma imikhondo kanye nayo yonke indiza yaphansi noma ingxenye yendiza ephansi ngqo ngaphansi kwayo. I-impedance yesici esakhiweni somugqa we-microstrip evamile isukela ku-50Ω ukuya ku-75Ω.

I-stripline entantayo ingenye indlela yokufaka izintambo nomsindo. Lo mugqa uqukethe izintambo ezinobubanzi obugxilile ongqimbeni lwangaphakathi kanye nendiza enkulu yaphansi phezulu nangaphansi kwekhondatha emaphakathi. Indiza ephansi ihlanganiswe phakathi kwendiza yamandla, ngakho-ke inganikeza umphumela osebenza kahle kakhulu wokumisa phansi. Lena indlela ekhethwayo yokugqokeka kwezintambo zesignali ye-PCB RF.

I-Coplanar waveguide inganikeza ukuhlukaniswa okungcono eduze kwesekethe ye-RF kanye nesekethe edinga ukuhanjiswa eduze. Lesi sikhungo siqukethe i-conductor emaphakathi nezindiza eziphansi kunoma yiluphi uhlangothi noma ngaphansi. Indlela engcono kakhulu yokudlulisa amasignali efrikhwensi yomsakazo ukumisa imigqa yemigqa noma ama-waveguides e-coplanar. Lezi zindlela ezimbili zinganikeza ukuhlukaniswa okungcono phakathi kwesiginali nokulandelelwa kwe-RF.

Kunconywa ukusebenzisa lokho okubizwa ngokuthi "ngocingo" kuzo zombili izinhlangothi ze-coplanar waveguide. Le ndlela inganikeza umugqa we-vias yomhlabathi endizeni ngayinye yensimbi yensimbi yomqhubi ophakathi. Umkhondo oyinhloko ogijima phakathi nendawo unocingo ohlangothini ngalunye, ngaleyo ndlela unikeze isinqamuleli se-return current emhlabathini ngezansi. Le ndlela inganciphisa izinga lomsindo elihambisana nomthelela omkhulu we-ripple yesiginali ye-RF. I-dielectric constant ye-4.5 ihlala ifana ne-FR4 material ye-prepreg, kuyilapho i-dielectric constant ye-prepreg-kusuka ku-microstrip, i-stripline noma i-offset stripline-ingaba ngu-3.8 kuya ku-3.9.

Kwamanye amadivaysi asebenzisa indiza ephansi, i-blind vias ingase isetshenziselwe ukuthuthukisa ukusebenza kokuxhuma kwe-capacitor yamandla futhi inikeze indlela ye-shunt kusuka kudivayisi ukuya phansi. Indlela ye-shunt eya phansi inganciphisa ubude be-via. Lokhu kungafeza izinjongo ezimbili: awugcini nje ngokudala i-shunt noma umhlabathi, kodwa futhi unciphisa ibanga lokudlulisela lamadivayisi anezindawo ezincane, okuyisici esibalulekile sokuklama kwe-RF.