Yintoni ulawulo lwe-impedance kunye nendlela yokwenza ulawulo lwe-impedance kwi-PCBs

Kuyilo lwezixhobo ze-elektroniki zanamhlanje, ii-PCB zidlala indima ebalulekileyo. Ukusebenza kwee-PCB kuchaphazela ngokuthe ngqo uzinzo, ukuthembeka kunye nokusebenza kakuhle kothumelo lwenkqubo yonke ye-elektroniki. Phakathi kwazo, ulawulo lwe-impedance yinxalenye ebalulekileyo yoyilo lwe-PCB. Ekubeni iisekethe zedijithali zanamhlanje zinamaxesha amafutshane othumelo lwesignali kunye namazinga aphezulu ewotshi, ii-trace ze-PCB aziselunxibelelwano lulula, kodwa ziintambo zothumelo ngokufanayo. Ulawulo lwe-impedance ye-PCB lubhekisa ekulawuleni isantya sothumelo kunye nokuhambelana kwe-impedance yesignali kwi-PCB ukuqinisekisa umgangatho kunye nozinzo lothumelo lwesignali.

Kwiimeko ezisebenzayo, kuyimfuneko ukulawula i-trace impedance xa isantya sedijithali esisezantsi siphezulu kune-1ns okanye i-analog frequency idlula i-300MHz. Enye yeeparameter eziphambili ze-PCB trace yi-characteristic impedance yayo (oko kukuthi, umlinganiselo we-voltage ukuya kumbane xa igagasi lidluliselwa kumgca wokuhambisa isignali). I-characteristic impedance yeengcingo kwi-PCB luphawu olubalulekileyo loyilo lwe-PCB. Ingakumbi kuyilo lwe-PCB olusebenzisa i-frequency ephezulu, kuyimfuneko ukuqwalasela ukuba i-characteristic impedance yengcingo iyahambelana okanye iyahambelana ne-characteristic impedance efunekayo yesixhobo okanye isignali. Oku kubandakanya iingcamango ezi-2: ulawulo lwe-impedance kunye nokuhambelana kwe-impedance. Eli nqaku ligxile kwimiba yolawulo lwe-impedance kunye noyilo lwe-stack.

Kukho imiqondiso eyahlukeneyo edluliselwa kwiikhondaktha zePCB. Ukuze kuphuculwe izinga lokudluliselwa kwayo, imvamisa yayo kufuneka inyuswe. Ixabiso le-impedance yesekethe ngokwayo liyahluka ngenxa yezinto ezinje ngokugrumba, ubukhulu beleya kunye nobubanzi bentambo, njl.njl., ezibangela ukuphazamiseka kwesignali. Ke ngoko, ixabiso le-impedance yeekhondaktha kwi-PCB ezikhawulezayo kufuneka lilawulwe ngaphakathi koluhlu oluthile, olubizwa ngokuba "lulawulo lwe-impedance".

Uxinzelelo lwee-traces ze-PCB lumiselwa yi-inductive kunye ne-capacitive inductance yazo, ukumelana kunye ne-conductivity coefficient. Izinto ezichaphazela uthintelo lweentambo ze-PCB ziquka ububanzi kunye nobukhulu bentambo yobhedu, i-dielectric constant kunye nobukhulu be-medium, ubukhulu be-solder pad, indlela yentambo yomhlaba, kunye noxinzelelo olujikeleze intambo, njl. Uluhlu lwe-PCB impedance yi-25 ukuya kwi-120 ohms.

Ngokwenyani, imigca yokudlulisa i-PCB idla ngokuba nomkhondo wentambo, umaleko omnye okanye ngaphezulu wesalathiso, kunye nezixhobo zokukhusela. Umkhondo kunye nomaleko zenza umqobo wokulawula. Ii-PCB zihlala zisebenzisa izakhiwo ezinamaleko amaninzi, kwaye ulawulo lwe-impedance lunokwakhiwa ngeendlela ezahlukeneyo. Nangona kunjalo, nokuba yeyiphi na indlela esetyenzisiweyo, ixabiso le-impedance liya kugqitywa bulwakhiwo lwayo kunye neempawu ze-elektroniki zezinto zokukhusela:

I-microstrip sisiqwenga sentambo esibhekisa kumgca wothumelo onecala elinye kuphela eline-reference plane. Umphezulu kunye namacala abonakala emoyeni (okanye agqunywe) kwaye abekwe kumphezulu we-insulation constant Er PCB, kunye nomaleko wamandla okanye womhlaba njengereferensi. Njengoko kubonisiwe kumfanekiso olandelayo:

Qaphela: Kwimveliso yePCB yokwenyani, umzi-mveliso wePCB udla ngokugquma umaleko we-inki eluhlaza kumphezulu wePCB. Ke ngoko, kubalo lokwenyani lwe-impedance, imodeli eboniswe kumfanekiso olandelayo idla ngokusetyenziselwa imigca ye-microstrip yomphezulu.

Umgca wentambo ngumcu wocingo obekwe phakathi kweenqwelo-moya ezimbini zesalathiso, njengoko kubonisiwe kumfanekiso olandelayo. Ii-dielectric constants ze-dielectric ezimelwe yi-H1 kunye ne-H2 zingahluka.

Ezi meko zimbini zingasentla ziyindlela eqhelekileyo yokubonisa i-microstrip kunye ne-striplines, ezisetyenziselwa ukufunda izixhobo ezikrelekrele ze-IoT ezifakwe ngaphakathi kunye nezinye iinkqubo. Kukho iintlobo ezininzi ezithile ze-microstrip kunye ne-striplines, ezifana ne-coated microstrip, ezinxulumene nesakhiwo esithile se-stacking se-PCBs.

I-equation esetyenziselwa ukubala i-characteristic impedance ifuna izibalo ezintsonkothileyo zezibalo, ngokuqhelekileyo kusetyenziswa iindlela zokusombulula intsimi, kuquka nohlalutyo lwezinto zomda. Ke ngoko, ngokusebenzisa isoftware yokubala i-impedance ekhethekileyo i-SI9000, esikufunayo kukulawula iiparameter ze-characteristic impedance:

I-dielectric constant Er yomaleko wokufaka ubushushu, ububanzi bocingo W1 kunye ne-W2 (trapezoidal), ubukhulu bocingo T, kunye nobukhulu bomaleko wokufaka ubushushu H.

Ububanzi bomgca obuyilwe ngu-W

Ukulahleka kwe-A - etch (jonga itheyibhile engentla)

Isizathu sobubanzi obungangqinelaniyo phakathi komphezulu nomzantsi womgca kukuba ngexesha lenkqubo yokwenziwa kwee-PCB, ukugqwala kwenzeka ukusuka phezulu ukuya ezantsi, nto leyo ebangela ukuba umgca ogqwalileyo ube yitrapezoidal.

Kukho ulwalamano oluhambelanayo phakathi kobukhulu bomgca u-T kunye nobukhulu bobhedu balo maleko, ngolu hlobo lulandelayo:

* Ngenxa yempembelelo encinci yobukhulu bemaski yesolder kwi-impedance, kucingelwa ukuba ixabiso layo lihlala lihleli yi-0.5mil.

Singafikelela kulawulo lwe-impedance ngokulawula ezi parameters. Sithatha i-PCB esezantsi ka-Anwei njengomzekelo, siza kuchaza amanyathelo olawulo lwe-impedance kunye nokusetyenziswa kwe-SI9000:

Umaleko wesibini yiplane yomhlaba, umaleko wesihlanu yiplane yamandla, kwaye ezinye iilayers ziyilayers zesignali.

Ingcaciso: I-dielectric phakathi kwee-intermediate layers yi-FR-4, ene-dielectric constant eyi-4.2; Ii-layers eziphezulu nezisezantsi zii-layers ezingenanto ezidibana ngqo nomoya, kwaye i-dielectric constant yomoya yi-1.

Abayili be-PCB banokusebenzisa ngokupheleleyo ulwakhiwo oluhambelanayo lwee-PCB ukuze bafumane ulawulo lwe-impedance. Ngokubeka iileya ezahlukeneyo zesignali kwiindawo ezahlukeneyo zeleya, i-interlayer capacitance kunye ne-inductance zinokulawulwa ngokufanelekileyo. Ngokubanzi, umaleko wangaphakathi usebenzisa izixhobo ze-impedance eziphezulu kwaye umaleko wangaphandle usebenzisa izixhobo ze-impedance ephantsi ukunciphisa impembelelo yokubonakalisa kunye ne-crosstalk.

Imigca yokudlulisa imiqondiso eyahlukeneyo inokubonelela ngesakhono esingcono sokulwa nokuphazamiseka kunye nomngcipheko ophantsi wokuthetha. Imigca yokudlulisa imiqondiso eyahlukeneyo yintambo ezimbini ezilinganayo ezine-voltages ezichaseneyo kodwa ezinobukhulu obulinganayo, ezinokubonelela ngesakhono esingcono sokulwa nokuphazamiseka. Ukuthintelwa kwemigca yokudlulisa imiqondiso eyahlukileyo kudla ngokulawulwa kukukhethwa kwesithuba semigca, ububanzi kunye nomhlaba.

Iiparameter zejiyometri ezifana nobubanzi bomgca we-PCB, isithuba kunye noyilo zingasetyenziselwa ukulawula i-impedance. Kwimigca eqhelekileyo ye-microstrip, ububanzi bomgca otyebileyo kunye nesithuba esikhulu kunokunciphisa i-impedance. Kwimigca ye-coaxial, ububanzi obuncinci bomgca wangaphakathi kunye ne-radii yomgca wangaphandle omkhulu kunokunyusa i-impedance. Ukukhethwa kwe-geometry ye-wiring kufuna ukulungiswa ngokusekelwe kwiimfuno ezithile ze-impedance kunye ne-frequency yesignali.

I-dielectric constant yezinto ze-PCB ikwachaphazela i-impedance. Ukukhetha izinto ezineempawu ze-dielectric ezizinzileyo yinxalenye yolawulo lwe-impedance. Kwizicelo ze-high-frequency kunye ne-high-speed, izinto ezisetyenziswa rhoqo ziquka i-FR-4 (ibhodi eqinisiweyo yefayibha yeglasi), i-PTFE (i-polytetrafluoroethylene), kunye ne-RF (i-radio frequency) laminates.

Ngaphambi koyilo lwe-PCB, ukusebenzisa izixhobo zokulinganisa kunye noyilo kunokunceda abayili ukuqinisekisa ngokukhawuleza nangokuchanekileyo kunye nokwenza ngcono i-impedance. Ezi zixhobo zinokulinganisa ukuziphatha kwesekethe, ukulahleka kokudluliselwa kwesignali kunye nokusebenzisana kwe-electromagnetic ukumisela iiparameter zoyilo lwe-PCB ezifanelekileyo. Ezinye izixhobo zokulinganisa eziqhelekileyo ziquka i-CST Studio Suite, i-HyperLynx kunye ne-ADS.

Ulawulo lwe-PCB impedance ludlala indima ebalulekileyo kwiisekethe zedijithali kunye neze-analog ezikhawulezayo. Ngokusebenzisa uyilo olufanelekileyo lwe-hierarchical, ukusetyenziswa kwemigca yokudlulisela isignali eyahlukileyo, ulawulo lwejometri yocingo, ukukhethwa kwezixhobo ze-PCB ezifanelekileyo, kunye nokusetyenziswa kwezixhobo zokulinganisa kunye noyilo, ulawulo oluchanekileyo lwe-impedance lunokufezekiswa, ngaloo ndlela kuphuculwe ukusebenza kwesekethe kunye nokuthembeka kwesignali.