Ukubonisa isignali kungase kubangele ukukhala. Ukukhala kwesignali okujwayelekile kuboniswa kuMfanekiso 1.

Ngakho-ke ukukhala kwesignali kwenzeka kanjani?

Njengoba kushiwo ngaphambili, uma ushintsho lwe-impedance luzwakala ngesikhathi sokudlulisa isignali, ukubonakaliswa kwesignali kuzokwenzeka. Le signali ingase ibe isignali ethunyelwe umshayeli, noma ingase ibe isignali ebonisiwe ebonakala ekugcineni. Ngokuvumelana nefomula ye-reflection coefficient, lapho isignali izwa ukuthi i-impedance iba yincane, ukubonakaliswa okungalungile kuzokwenzeka, futhi i-voltage ebonisiwe engalungile izobangela isignali ukuthi ihlehlise phansi. Isignali ibonakala izikhathi eziningi phakathi komshayeli nomthwalo werimothi, futhi umphumela uwukukhala kwesignali. I-impedance yokukhiphayo yama-chips amaningi iphansi kakhulu. Uma i-impedance yokuphumayo ingaphansi kwesici se-impedance ye PCB ukulandelela, ukukhala kwesignali kuzokwenzeka nakanjani uma kungekho ukunqanyulwa komthombo.

Inqubo yokukhala kwesignali ingachazwa ngokunembile ngomdwebo wokugxuma. Kucatshangwa ukuthi ukuvimbela okukhiphayo kokuphela kwedrayivu kungu-10 ohms, futhi isici esivimbela ukulandelwa kwe-PCB singama-ohms angu-50 (singashintshwa ngokushintsha ububanzi bokulandelela kwe-PCB, ubukhulu be-dielectric phakathi kwe-PCB trace kanye nereferensi yangaphakathi. indiza), ukuze kube lula ukuhlaziya, ake sithi isiphetho esikude sivulekile , Okusho ukuthi, i-impedance ekude ayinamkhawulo. Isiphetho sedrayivu sidlulisa isignali ye-voltage engu-3.3V. Masilandele isignali futhi sigijime kulo mzila wokudlulisela kanye ukuze sibone ukuthi kwenzekeni. Ukuze kube lula ukuhlaziya, ithonya le-parasitic capacitance kanye ne-parasitic inductance yomugqa wokudlulisela ayinakwa, futhi imithwalo yokumelana kuphela ibhekwa. Umfanekiso wesi-2 uwumdwebo wohlelo lokuzindla.

Ukubonakaliswa kokuqala: isiginali ithunyelwa isuka ku-chip, ngemuva kokuphazamiseka kokuphuma kwe-10 ohm kanye ne-50 ohm PCB yesici, isiginali engezwe kumkhondo we-PCB yi-voltage endaweni A 3.3*50/(10+50)=2.75 V. Ukudluliselwa endaweni eyihlane B, ngoba iphuzu B livuliwe, i-impedance ayinamkhawulo, futhi i-coefficient yokubonisa ingu-1, okungukuthi, wonke amasignali aboniswa, futhi isignali ebonisiwe nayo i-2.75V. Ngalesi sikhathi, i-voltage elinganisiwe endaweni engu-B ingu-2.75+2.75=5.5V.

Ukubonakaliswa kwesibili: i-voltage ebonisiwe engu-2.75V ibuyela endaweni A, i-impedance iyashintsha isuka ku-50 ohms iye ku-10 ohms, ukubonakaliswa okungekuhle kwenzeka, i-voltage ebonisiwe endaweni A ingu-1.83V, i-voltage ifinyelela endaweni engu-B, futhi ukubonakaliswa kuyenzeka futhi, futhi i-voltage ebonisiwe yi–1.83 V. Ngalesi sikhathi, i-voltage elinganisiwe endaweni B ingu-5.5-1.83-1.83 = 1.84V.

Ukuboniswa kwesithathu: I-voltage engu–1.83V eboniswa ukusuka endaweni engu-B ifika endaweni engu-A, futhi ukubonakaliswa okungekuhle kuphinde kwenzeke, futhi i-voltage ebonisiwe ingu-1.22V. Lapho i-voltage ifinyelela endaweni engu-B, ukuboniswa okuvamile kwenzeka futhi, futhi i-voltage ebonisiwe ingu-1.22V. Ngalesi sikhathi, i-voltage elinganisiwe endaweni engu-B ingu-1.84+1.22+1.22=4.28V.

Kulo mjikelezo, i-voltage ebonisiwe igxuma iye emuva naphambili phakathi kwephoyinti A nephoyinti B, okwenza i-voltage ephoyinti B ukuthi ingazinzi. Bheka i-voltage endaweni engu-B: 5.5V->1.84V->4.28V->……, kungabonakala ukuthi i-voltage endaweni engu-B izoguquguquka iye phezulu naphansi, okuwukukhala kwesiginali.

Kwenzeka kanjani ukukhala kwesiginali kusekethe ye-PCB?

Imbangela eyinhloko yokukhala kwesignali ibangelwa ukucabangela okungalungile, futhi umlandu usengushintsho lwe-impedance, okuphinde kube yi-impedance! Uma ufunda izindaba zobuqotho besignali, hlala unaka izinkinga ze-impedance.

Ukukhala kwesignali ekugcineni komthwalo kuzophazamisa kakhulu ukwamukela isignali futhi kubangele amaphutha okunengqondo, okumele kuncishiswe noma kuqedwe. Ngakho-ke, ukunqanyulwa okufanayo kwe-impedance kufanele kwenziwe kumalayini amade okudlulisela.