Ukubonakalisa umqondiso kunokubangela ukukhala. Ukukhala komqondiso oqhelekileyo kuboniswe kuMfanekiso 1.

Ke kwenzeka njani ukukhala komqondiso?

Njengoko kukhankanyiwe ngaphambili, ukuba utshintsho kwi-impedance luvakala ngexesha lokuhanjiswa kwesignali, ukubonakalisa umqondiso kuya kwenzeka. Olu phawu lusenokuba luphawu oluthunyelwe ngumqhubi, okanye lusenokuba luphawu olubonakalisiweyo oluvela kwicala elikude. Ngokwefomula ye-coefficient yokubonisa, xa umqondiso uvakalelwa kukuba i-impedance iba yincinci, ukubonakaliswa okungalunganga kuya kwenzeka, kwaye i-voltage engabonakaliyo ebonakalisiweyo iya kubangela ukuba umqondiso ungaphantsi. Isignali ibonakaliswa ngamaxesha amaninzi phakathi komqhubi kunye nomthwalo okude, kwaye umphumo kukukhala komqondiso. Imveliso ye-impedance yeechips ezininzi iphantsi kakhulu. Ukuba i-impedance yemveliso ingaphantsi kwe-impedance yeempawu ze PCB umkhondo, ukukhala komqondiso kuyakwenzeka ngokungenakuthintelwa ukuba akukho mthombo wokupheliswa.

Inkqubo yokukhala kwesignali inokuchazwa ngokuzenzekelayo ngedayagram ye-bounce. Kucingelwa ukuba ukungasebenzi kwemveliso yokuphela kwe-drive yi-10 ohms, kwaye uphawu lokuthintela umkhondo we-PCB luyi-50 ohms (inokulungelelaniswa ngokutshintsha ububanzi bomkhondo wePCB, ubukhulu bedielectric phakathi komkhondo wePCB kunye nereferensi yangaphakathi. plane), ukwenzela ukuba kube lula ukuhlalutya, cinga ukuba isiphelo esikude sivulekile , Oko kukuthi, i-impedance ekude ayinasiphelo. Isiphelo sokuqhuba sihambisa isibonakaliso se-voltage ye-3.3V. Masilandele umqondiso kwaye sibaleke kule ntambo yothumelo kube kanye ukubona ukuba kwenzeke ntoni. Ukuze kube lula ukuhlalutya, impembelelo ye-parasitic capacitance kunye ne-parasitic inductance yomgca wokuhambisa ayihoywa, kwaye imithwalo yokumelana kuphela iyaqwalaselwa. Umzobo 2 ngumzobo weskim wokubonisa.

Umboniso wokuqala: umqondiso uthunyelwa ngaphandle kwe-chip, emva kwe-10 ohm i-impedance ye-impedance kunye ne-50 ohm ye-PCB ye-impedance yeempawu, uphawu olufakwe kwi-PCB trace yi-voltage kwindawo A 3.3 * 50 / (10 + 50) = 2.75 V. Ukuhanjiswa kwindawo ekude B, kuba i-point B ivulekile, i-impedance ayinasiphelo, kwaye i-coefficient yokubonisa i-1, oko kukuthi, zonke iimpawu zibonakaliswe, kwaye isibonakaliso esibonakalisiweyo sikwa-2.75V. Ngeli xesha, umbane olinganisiweyo kwinqanaba B ngu-2.75 + 2.75 = 5.5V.

Umboniso wesibini: i-2.75V ebonakalisiweyo yombane ibuyela kwindawo A, utshintsho lwe-impedance ukusuka kwi-50 ohms ukuya kwi-10 ohms, ukubonakaliswa okungalunganga kwenzeka, i-voltage ebonakalisiweyo kwindawo A yi-1.83V, i-voltage ifikelela kwindawo B, kwaye ukubonakaliswa kuyenzeka kwakhona; kunye ne-voltage ebonakalisiweyo -1.83 V. Ngeli xesha, i-voltage elinganisiweyo kwindawo B yi-5.5-1.83-1.83 = 1.84V.

Umboniso wesithathu: I-voltage ye–1.83V ebonakaliswe ukusuka kwindawo B ifikelela kwindawo A, kwaye ukubonakaliswa okungalunganga kwenzeka kwakhona, kwaye umbane obonakalisiweyo ngu-1.22V. Xa i-voltage ifikelela kwindawo B, ukubonakaliswa rhoqo kwenzeka kwakhona, kwaye i-voltage ebonakalisiweyo yi-1.22V. Ngeli xesha, i-voltage elinganisiweyo kwindawo B yi-1.84 + 1.22 + 1.22 = 4.28V.

Kulo mjikelo, i-voltage ebonakalisiweyo igxuma ngasemva naphambili phakathi kwendawo A kunye nenqaku B, ibangela ukuba i-voltage kwindawo B ingazinzi. Qwalasela i-voltage kwindawo B: 5.5V->1.84V->4.28V->……, kunokubonwa ukuba i-voltage kwindawo ye-B iya kuhla inyuka inyuka, iyindlela yokukhala kwesignali.

Kwenzeka njani ukukhala komqondiso kwisekethe yePCB?

Ingcambu yesizathu sokukhala kwesignali ibangelwa ukubonakalisa okungalunganga, kwaye umtyholwa useyinguqu ye-impedance, ephinda i-impedance! Xa ufunda imiba yengqibelelo yesiginali, hlala ubeke ingqalelo kwimiba ye-impedance.

Ukukhala komqondiso ekupheleni komthwalo kuya kuphazamisa kakhulu ukwamkelwa komqondiso kwaye kubangele iimpazamo ezinengqondo, ekufuneka zincitshiswe okanye zipheliswe. Ke ngoko, ukupheliswa kokuhambelana kwe-impedance kufuneka kwenziwe kwiintambo zosulelo olude.