Cov luag hauj lwm ntawm resistors nyob rau hauv series.
Vim hais tias qhov impedance ntawm lub teeb liab qhov chaw yog tsawg heev, thiab impedance ntawm lub teeb liab kab tsis sib xws, tom qab lub series ntawm ib tug resistor, koj muaj peev xwm txhim kho qhov sib txuam qhov teeb meem kom txo tau reflections, kom tsis txhob oscillations, thiab lwm yam.
Cov txheej txheem sib piv impedance
1. Siv transformer los ua impedance conversion.
2. kev siv cov series / parallel capacitors los yog inductors, uas yog feem ntau siv nyob rau hauv debugging RF circuits.
3. siv txoj hauv kev ntawm series / parallel resistors. Qee tus neeg tsav tsheb muaj qhov impedance qis, koj tuaj yeem txuas tus resistor tsim nyog nyob rau hauv series kom phim cov kab sib kis, xws li cov kab teeb liab ceev ceev, qee zaum hauv series nrog ob peb lub kaum ohms ntawm kev tiv thaiv. Thiab qee cov receivers yog siab dua input impedance, koj tuaj yeem siv txoj kev sib txuas ntawm cov resistor kom phim nrog cov kab sib kis, piv txwv li, 485 tsheb npav receiver, feem ntau nyob rau hauv parallel nrog cov ntaub ntawv kab davhlau ya nyob twg 120 ohms txuam resistor.
4. hloov lub impedance quab yuam. Kho qhov load impedance tus nqi los ntawm kev sib txuas thiab sib txuas ntawm capacitors, inductors thiab loads kom ua tiav qhov chaw thiab thauj khoom impedance txuam.
5. Kho cov kab sib kis. Kho cov kab kis tau tus mob yog kom ntev qhov kev ncua deb ntawm qhov chaw thiab cov load, nrog capacitors thiab inductors los kho cov impedance quab yuam mus rau xoom. Thaum lub sijhawm no, lub teeb liab yuav tsis tawm, lub zog tuaj yeem nqus tau los ntawm kev thauj khoom. Kev kub ceev PCB thaiv, kev sib dhos dav dav ntawm cov teeb liab digital yog tsim los rau 50 ohms. Txoj cai dav dav yog tias coaxial cable baseband 50 ohms, zaus band 75 ohms, twisted khub (differential) rau 85-100 ohms.
Vim hais tias cov resistor series, nrog rau cov teeb liab kab tis capacitance thiab load input capacitance, thiab lwm yam los tsim ib tug RC Circuit Court, uas yuav txo tau lub steepness ntawm lub teeb liab ntug. Raws li koj paub, yog hais tias tus ntug ntawm lub teeb liab yog ntxhab heev, muaj ib tug loj tus naj npawb ntawm high-frequency Cheebtsam, yuav muaj hluav taws xob cuam tshuam, nyob rau hauv tas li ntawd, kuj yooj yim rau tsim overshoot.
Feem ntau, kev siv xws li ib tug resistor yog xam tsuas yog nyob rau hauv high-ceev teeb liab kab. Nyob rau hauv cov ntaub ntawv tsawg zaus, nws feem ntau yog kev sib txuas ncaj qha.
Tshooj tom ntej yuav piav qhia txog lub luag haujlwm ntawm resistor series txuas nrog cov xwm txheej tshwj xeeb.
1. SPI teeb liab kab
SPI teeb liab ntawm lub series resistor, feem ntau ob peb kaum ntawm ohms los yog li ntawd, feem ntau muaj lub luag haujlwm hauv qab no.
a. impedance piv. Vim hais tias qhov impedance ntawm lub teeb liab qhov chaw yog tsawg heev, thiab impedance ntawm lub teeb liab kab tsis sib xws, tom qab lub series ntawm ib tug resistor, tuaj yeem txhim kho qhov kev sib txuam kom txo tau qhov kev xav.
b. SPI tus nqi yog siab, ib tug resistor nyob rau hauv series, nrog rau cov kab capacitor thiab load capacitance los tsim ib tug RC Circuit Court kom txo tau cov teeb liab steepness thiab tsis txhob overshoot, overshoot tej zaum yuav puas lub nti GPIO, ntawm chav kawm, EMI kuj zoo, tshwj xeeb tshaj yog high-ceev Circuit Court.
c. debugging yooj yim, ntau cov chips yog tam sim no BGA, QFN pob, ib tug resistor nyob rau hauv series, debugging nrog ib tug oscilloscope mus ntes lub waveform yog yooj yim.
2. LDO tswv yim
Thaum lub LDO VIN qhov siab tshaj plaws nyob ze rau lub hwj chim mov voltage, lub sij hawm no thiab tsis xav hloov lub siab specification LDO, thiaj li yuav txuag tau nqi, ces koj muaj peev xwm hlua ib tug me me kuj resistor, muaj peev xwm nqus ib feem ntawm qhov voltage thiab tam sim no. , thaum lub hwj chim mov sab ntawm ib tug loj surge, lub resistor yuav ua ntej los ntawm ib tug me me nqi.
Piv txwv li LDO tawg, VIN thiab GND luv luv Circuit Court, vim tias muaj cov resistor R, kuj tseem yuav zam lub zog SYS_5V thiab GND luv Circuit Court.
3. TVS ua ntej thiab tom qab series resistor
TVS series resistors feem ntau txuas nrog ob txoj hauv kev, thawj daim duab resistor nyob rau hauv pem hauv ntej ntawm TVS, qhov thib ob daim duab resistor tom qab TVS, ob qhov kev siv hluav taws xob tsis zoo ib yam.
a. Rau thawj daim duab, ua ntej xav txog qhov loj ntawm qhov surge, yog tias tsis loj, koj tuaj yeem xaiv qhov tsim nyog lub zog resistor, lub resistor nyob rau hauv pem hauv ntej ntawm lub TVS, yuav nqus ib feem me me ntawm tam sim no, tom qab lub surge tam sim no IPP me me, Raws li cov TVS Vc (clamp voltage) kuj yuav ua me me, kev tiv thaiv zoo dua rau lub nraub qaum-kawg.
b. rau daim duab thib ob, TVS thawj zaug nqus feem ntau ntawm cov inrush tam sim no, ib feem ntawm qhov seem seem lossis qhov seem tam sim no, yuav dhau los ntawm cov resistor R2, qhov thib ob voltage divider tam sim no txwv, tuaj yeem tiv thaiv lub nraub qaum kawg. Yog hais tias lub back-kawg load loj dua R2, voltage divider tam sim no limiting yuav tsawg, R2 yeej tsis muaj lub luag hauj lwm.