Teeb pom kev zoo yuav ua rau lub suab nrov. Ib lub suab nrov nrov yog pom hauv daim duab 1.

Yog li cas lub teeb liab ringing tshwm sim?

Raws li tau hais ua ntej, yog tias muaj kev hloov pauv hauv impedance tau hnov ​​thaum lub teeb liab kis tau tus mob, lub teeb liab yuav tshwm sim. Cov teeb liab no yuav yog lub teeb liab xa los ntawm tus neeg tsav tsheb, lossis nws yuav yog lub teeb liab cuam tshuam los ntawm qhov kawg. Raws li cov qauv kev xav coefficient, thaum lub teeb liab pom tau tias qhov impedance ua me me, qhov kev xav tsis zoo yuav tshwm sim, thiab qhov cuam tshuam tsis zoo yuav ua rau lub teeb liab tsis zoo. Lub teeb liab tau cuam tshuam ntau zaus ntawm tus neeg tsav tsheb thiab cov chaw taws teeb load, thiab qhov tshwm sim yog teeb liab ringing. Cov zis impedance ntawm feem ntau cov chips yog tsawg heev. Yog hais tias cov zis impedance tsawg dua tus yam ntxwv impedance ntawm lub PCB kab, teeb liab ringing yuav inevitably tshwm sim yog tias tsis muaj qhov chaw txiav.

Cov txheej txheem ntawm lub teeb liab ringing tuaj yeem piav qhia qhov tseeb ntawm daim duab bounce. Piv txwv tias qhov tso zis impedance ntawm tus tsav kawg yog 10 ohms, thiab cov yam ntxwv impedance ntawm PCB kab yog 50 ohms (tuaj yeem hloov kho los ntawm kev hloov qhov dav ntawm PCB kab, qhov tuab ntawm dielectric ntawm PCB kab thiab cov ntaub ntawv sab hauv dav hlau), rau qhov yooj yim ntawm kev tsom xam, piv txwv li qhov chaw taws teeb kawg yog qhib, Qhov ntawd yog, qhov kawg impedance yog infinite. Qhov kawg tsav xa tawm 3.3V voltage teeb liab. Cia peb ua raws li lub teeb liab thiab khiav los ntawm kab sib kis no ib zaug kom pom tias muaj dab tsi tshwm sim. Rau qhov yooj yim ntawm kev tsom xam, kev cuam tshuam ntawm parasitic capacitance thiab parasitic inductance ntawm cov kab kis tau tus mob yog tsis quav ntsej, thiab tsuas yog cov loads resistive xwb. Daim duab 2 yog daim duab schematic ntawm kev xav.

Thawj qhov kev xav: lub teeb liab raug xa tawm ntawm lub nti, tom qab 10 ohm tso zis impedance thiab 50 ohm PCB yam ntxwv impedance, lub teeb liab tau ntxiv rau PCB kab yog qhov voltage ntawm point A 3.3 * 50 / (10 + 50) = 2.75 V. Kev xa mus rau qhov chaw deb B, vim hais tias taw tes B yog qhib, qhov impedance yog infinite, thiab lub reflection coefficient yog 1, uas yog, tag nrho cov teeb liab yog reflected, thiab reflected teeb liab kuj yog 2.75V. Lub sijhawm no, ntsuas qhov hluav taws xob ntawm point B yog 2.75 + 2.75 = 5.5V.

Qhov kev xav thib ob: 2.75V qhov hluav taws xob rov qab mus rau taw tes A, qhov impedance hloov ntawm 50 ohms mus rau 10 ohms, qhov kev xav tsis zoo tshwm sim, qhov cuam tshuam qhov hluav taws xob ntawm qhov taw tes A yog -1.83V, qhov hluav taws xob ncav cuag point B, thiab qhov kev xav rov tshwm sim dua, thiab qhov cuam tshuam qhov hluav taws xob yog -1.83 V. Lub sijhawm no, qhov ntsuas hluav taws xob ntawm point B yog 5.5-1.83-1.83 = 1.84V.

Qhov kev xav thib peb: Qhov -1.83V qhov hluav taws xob cuam tshuam los ntawm point B mus txog qhov point A, thiab qhov kev xav tsis zoo tshwm sim dua, thiab qhov cuam tshuam qhov hluav taws xob yog 1.22V. Thaum qhov hluav taws xob mus txog qhov point B, qhov kev xav tsis tu ncua tshwm sim dua, thiab qhov cuam tshuam qhov hluav taws xob yog 1.22V. Lub sijhawm no, qhov ntsuas hluav taws xob ntawm point B yog 1.84 + 1.22 + 1.22 = 4.28V.

Nyob rau hauv lub voj voog no, qhov cuam tshuam qhov hluav taws xob rov qab los ntawm qhov point A thiab point B, ua rau qhov voltage ntawm point B tsis ruaj khov. Saib xyuas qhov voltage ntawm point B: 5.5V-> 1.84V-> 4.28V->……, nws tuaj yeem pom tias qhov hluav taws xob ntawm point B yuav hloov pauv nce thiab nqis, uas yog lub suab nrov.

Lub teeb liab ringing hauv PCB Circuit Court tshwm sim li cas?

Lub hauv paus ua rau lub teeb liab ringing yog tshwm sim los ntawm kev xav tsis zoo, thiab tus neeg ua txhaum tseem hloov pauv impedance, uas yog rov impedance! Thaum kawm txog teeb meem kev ncaj ncees, nco ntsoov xyuam xim rau cov teeb meem impedance.

Lub teeb liab ringing ntawm qhov kawg load yuav cuam tshuam nrog lub teeb liab txais tos thiab ua rau cov logic yuam kev, uas yuav tsum tau txo los yog tshem tawm. Yog li ntawd, impedance txuam kev txiav txim yuav tsum tau ua rau ntev kis kab.