Hauv cov hluav taws xob hluav taws xob, cov mestal oscillator yog ib qho ntawm feem ntau cov moos. Txhawm rau kom muaj cov crystal oscillator pib ib txwm muaj thiab ua haujlwm ruaj khov, sab nraud tsim hluav taws xob yuav tsum tau tsim raws nws cov load capacitance (xa mus rau raws li CLE). Cov peev xwm tsis tsim nyog tuaj yeem ua rau muaj kev nyuaj thaum pib oscillation, ntau zaus sib txawv, lossis txawm tias qhov system tsis muaj peev xwm.
Kab lus no yuav nthuav qhia cov ntsiab lus ntawm crystal crystal oscillator load muaj peev xwm capacitance, kev txiav txim siab suav ntawm cov qauv hluav taws xob.
1. Dab tsi yog lub load Captance (CL) ntawm cov siv lead ua ke?
Crystal oscillator cov tuam ntxhab feem ntau qhia meej rau nominal load Cap Captance tus nqi ntawm cov siv lead ua
Hauv lwm lo lus, lub crystal oscillator tuaj yeem tso tawm qhov muaj tseeb tsuas yog thaum sib npaug ntawm load Capacitance sib npaug cl.
2. Yuav ua li cas cov chaw sab nraud capacitors cuam tshuam rau kev thauj khoom siv tau?
Ib qho kev ua lead ua oscillator Circilator yog raws li hauv qab no:
C1 thiab C2 yog ob lub capacitors sib txuas sab nraud mus rau Gnd (feem ntau chip congritors);
Ob qho kawg ntawm XTAL tau txuas nrog ob lub pins ntawm lub lead ua oscillator feem;
Qhov tseeb, qhov sib npaug ntsaws ruaj ruaj cl ntawm lub crystal oscillator tau txais ntawm C1 thiab C2, ntxiv rau Parasitic Capital Capacitance CP tau qhia los ntawm PCB Board thiab ntim khoom.
3. Kev muab cov lej cais: Yuav ua li cas rau kev tsim nyog sab nraud muaj nuj nqis raws li cl?
Cov qauv rau cov load sib npaug capacitance (CL) yog raws li hauv qab no:
Khij:
C1, C2: capacitors txuas nrog sab nraud rau gnd;
CP: Parasiticic capacitance qhia los ntawm PCB kab, ntim, thiab lwm yam (feem ntau yog 2pf ~ 5pf, uas tuaj yeem kwv yees los ntawm kev simulation lossis kev paub);
Cl: nominal load muaj peev xwm muab tso rau hauv cov ntaub ntawv mexillator datashators.
[Piv txwv li lus piv txwv]
Xav tias cov siv leCillator specification yog cl=18 pa, thiab pcb parasitical cap cap cP ≈ 5PF. Yuav kom tau txais txiaj ntsig C1 tsim nyog thiab C2:
Ua ntej hloov mus rau cov qauv:
Xav tias c 1 =}}}}} C, cov mis piv rau:
Kev daws rau C:
Yog li ntawd, nws raug nquahu kom siv cov chaw sab nraud capacitors c 1 =2=27 pf (tus nqi txheem).
4. Vim li cas mismatched sab nraud hluav taws xob muaj teeb meem?
Zaus striation: Yog hais tias sab nraud hluav taws xob me me lossis loj dhau, lub crystal oscillator yuav txawv ntawm nws cov nominal zaus yuav txawv txav;
Nyuaj lossis tsis ruaj khov oscillation: ntau dhau kev thauj khoom yuav txo nce, uas yuav ua rau cov muaj lead ua oscillator kom tsis pib oscillating lossis muaj ntau lub jitter;
Kev noj ntau zog: Kev thauj khoom tsis zoo yuav ua rau muaj zog siv hluav taws xob ntawm cov crystal oscillator Circuitator;
Qaug EMI: Tsis khov oscillation tej zaum yuav tsim cov xwm txheej tsis txaus ntseeg, cuam tshuam rau lub tshuab hluav taws xob hluav taws xob raug cai ntawm cov kab ke.
5. Cov lus pom zoo tsim thiab kev coj ua engineering
Ua tib zoo saib cov crystal oscillator datasheet
Qhia meej tus nqi Cl;
Qhia meej cov kev pom zoo ntawm cov toinc;
Kuaj xyuas yog tias muaj kev pom zoo ntawm ntau ntawm cov peev xwm sab nraud muaj peev xwm tau muab.
Xav txog qhov tseeb ntawm pawg thawj coj saib
Kwv yees CP siv pcb simulation los yog kev paub;
Txog siab - ceev lossis precision moos (piv txwv, lub zog sib txuas lus> 100mHz), pom zoo xam.
Siv cov khoom siv capmitric
Feem ntau, nws raug nquahu tias c1=C2 los ua kom yog qhov ntsuas zaus thiab tshuav nyiaj nrov;
Kev tsim kho asympetric kuj tseem siv tau yog tias muaj cov kev tshwj xeeb tshwj xeeb.
Siv Chip Capacitor arsays thaum debugging
Cov kev sib tw tuaj yeem ua tiav nrog Chip Capressors (piv txwv li, 10pf, 15pf, 27pf, 27pf, thiab lwm yam);
Siv tshuaj pleev ib ce spectrum lossis oscilloscope kom kuaj cov khoom ruaj khov thiab zaus raug.
6. Cov lus nug tsis sib haum (FAQ)
Lo lus nug teb
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Lus nug |
Teb |
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Yog hais tias cl =12 pa, qhov loj me yuav tsum muaj lub peev xwm sab nraud? |
Piv txwv CP =5 pf, ces c 1=} C2≈14pf |
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Vim li cas qee cov Mcus tsis xav tau cov chaw sab nraud? |
Qee cov crystal oscillator circuits muaj cov ntsaws ruaj ruaj ruaj ruaj sab hauv (piv txwv li, stm32), yog li tsis muaj kev sib txuas sab nraud |
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Puas yog mismatched sab nraud cacacitors hlawv cov crystal oscillator? |
Feem ntau tsis, tab sis nws yuav ua rau oscillation tsis ua hauj lwm lossis ua yuam kev os |
Tag
Tus qauv tsim ntawm sab nraud oscitance rau cov crystal oscillator yog ib qho kev nthuav dav me me uas cuam tshuam ncaj qha cuam tshuam nrog kev ruaj ntseg thiab qhov tseeb ntawm lub moos. Nkag siab txog kev sib sau ua ke ntawm Cl thiab C1 / C2, thiab kho kom haum PCB parasitical capacitance, yog tus yuam sij kom ua tiav stable oscillation thiab muaj pes tsawg zaus.
Nyob rau hauv high - Cov khoom siv ceev digital, cov khoom siv sib txuas lus, lossis siv cov crystal mib xaim hluav taws xob uas yuav tsum tau ua haujlwm hnyav.
Hangjing muaj cov kws tshawb fawb kev tshaj lij thiab muaj pes tsawg tus neeg ua ntawv thov sib tw ua haujlwm, uas tuaj yeem muab cov neeg siv khoom sib tw dawb. Yog tias koj muaj kev xav tau zoo li no, thov koj xav tiv tauj peb cov neeg ua haujlwm muag lossis cov neeg ua haujlwm.