Ezimweni eziningi, PCB izintambo zizodlula emigodini, amapayipi ezindawo zokuhlola, imigqa emifushane yesikhonkwane, njll., Zonke zinamandla okuqina, okuzophazamisa nakanjani isignali. Ithonya le-capacitance kusiginali kufanele lihlaziywe kusukela ekugcineni okudlulisayo nasekupheleni kokuthola, futhi kunomthelela endaweni yokuqala nasekupheleni.

Qhafaza kuqala ukubona umthelela kusidlulisi sesiginali. Lapho isignali yesinyathelo esanda ngokushesha ifinyelela ku-capacitor, i-capacitor ikhokhiswa ngokushesha. Okwamanje ukushaja kuhlobene nokuthi amandla wesiginali akhuphuka ngokushesha kangakanani. Ifomula yamanje yokushaja ithi: I = C * dV / dt. Ukuphakama kwe-capacitance, ukuphakama kwamanje kokushaja, isikhathi sokuphakama kwesiginali sishesha, i-dt encane, nayo yenza ukuba manje ukushaja kuphakame.

Siyazi ukuthi ukubonakaliswa kwesiginali kuhlobene nokushintshwa kwe-impedance inzwa yesiginali, ngakho-ke ukuhlaziywa, ake sibheke ushintsho lwe-impedance olwenziwa yi-capacitance. Esigabeni sokuqala sokushaja kwe-capacitor, impedance ivezwa njengo:

Lapha, i-dV empeleni inguquko yamandla esignali yesinyathelo, i-dt yisikhathi sokuvuka kwesiginali, futhi ifomula ye-impedance ye-capacitance iba:

Kule fomula, singathola imininingwane ebaluleke kakhulu, lapho isiginali yesinyathelo isetshenziswa esigabeni sokuqala kuzo zombili iziphetho ze-capacitor, impedance ye-capacitor ihlobene nesikhathi sokuvuka kwesiginali namandla ayo.

Imvamisa esigabeni sokuqala sokushaja kwe-capacitor, i-impedance incane kakhulu, incane kune-impedance yesici sezintambo. Ukuboniswa okungalungile kwesiginali kwenzeka ku-capacitor, futhi isignali ye-voltage engemihle iphakanyiswe nesiginali yoqobo, okuholela ekwehleni kwesiginali kusidluliseli naku-non-monotonic yesiginali kulidlulisela.

Okokugcina okwamukelayo, ngemuva kokuthi isignali ifike ekugcineni kokutholwa, kwenzeka ukubonakaliswa okuhle, isignali ekhonjisiwe ifinyelela endaweni ye-capacitor, lolo hlobo lokuboniswa okungalungile lwenzeka, futhi amandla we-reflection voltage akhonjiswe emuva ekugcineni okwamukelayo nawo abangela isignali ekwamukelweni end ukukhiqiza ukwehla.

Ukuze umsindo obonisiwe ube ngaphansi kuka-5% we-voltage swing, obekezelelekayo kusiginali, ushintsho lwe-impedance kufanele lube ngaphansi kuka-10%. Ngakho-ke kufanele yini ukuthi i-capacitance impedance ibe? I-Capacitance impedance iyi-impedance efanayo, futhi singasebenzisa ifomula ye-impedance efanayo kanye nefomula ye-coefficient yokubonisa ukunquma ububanzi bayo. Kule mpedance efanayo, sifuna ukuthi i-capacitance impedance ibe nkulu ngangokunokwenzeka. Uma ucabanga ukuthi i-capacitance impedance yizikhathi ze-K zensimbi ye-PCB ye-impedance yesici, i-impedance ezwa yisiginali ku-capacitor ingatholakala ngokuya ngefomula ye-impedance efanayo:

Okungukuthi, ngokusho kwalesi sibalo esikahle, i-impedance ye-capacitor kufanele okungenani ibe yizikhathi eziyi-9 i-impedance yesici se-PCB. Eqinisweni, njengoba kukhokhiswa i-capacitor, i-impedance ye-capacitor iyakhula futhi ayihlali i-impedance ephansi njalo. Ngaphezu kwalokho, idivaysi ngayinye ingaba ne-inductance ye-parasitic, ekhulisa i-impedance. Ngakho-ke lo mkhawulo ophindwe kasishiyagalolunye ungakhululeka. Engxoxweni elandelayo, cabanga ukuthi umkhawulo uyizikhathi ezi-5.

Ngesibonisi se-impedance, singanquma ukuthi ingakanani amandla we-capacitance angabekezelelwa. I-50 ohms impedance yesici ebhodini lesifunda ivame kakhulu, ngakho-ke ngisebenzise ama-50 ohms ukuyibala.

Kuphetha ngokuthi:

Kulokhu, uma isikhathi sokuvuka kwesiginali singama-1ns, amandla angaphansi kwama-picograms ama-4. Ngakolunye uhlangothi, uma i-capacitance ingama-picograms ama-4, isikhathi sokuvuka kwesiginali ngu-1ns ngokuhamba phambili. Uma isikhathi sokuvuka kwesiginali singama-0.5ns, le-4 picograms capacitance izodala izinkinga.

Ukubalwa lapha kuchaza kuphela umthelela we-capacitance, isekethe langempela liyinkimbinkimbi kakhulu, kunezinto eziningi okudingeka zicatshangelwe, ngakho-ke ukuthi ukubalwa lapha kunembile akubalulekile yini. Okusemqoka ukuqonda ukuthi amandla we-capacitance asithinta kanjani isignali ngalesi sibalo. Lapho sesinokuqonda okubonakalayo komthelela wento ngayinye ebhodini lesifunda, singanikeza ukuholwa okudingekayo ekwakhiweni futhi sazi ukuthi singahlaziya kanjani izinkinga lapho zenzeka. Izilinganiso ezinembile zidinga ukulingiswa kwesoftware.

Isiphetho:

1. Umthwalo we-capacitive ngesikhathi se-PCB umzila ubangela ukuthi isignali yokudlulisa iphele ukukhiqiza ukwehla, futhi isinali lokuphela komamukeli nalo lizokhiqiza ukwehla.

2. Ukubekezelelana kwe-capacitance kuhlobene nesikhathi sokuvuka kwesiginali, lapho isikhathi sokwanda kwesiginali sishesha, kuncane ukubekezelelana kwamandla.