Ka'idodin Zane da La'akari da Zaɓuɓɓuka don Matsakaicin Juzu'i a cikin Crystal Oscillators
A cikin ƙirar tsarin agogon kayan aiki, injiniyoyi sukan haɗu da nau'in mitoci na oscillator masu kama da "marasa daidaituwa", kamar 11.0592 MHz, 3.579545 MHz, da 19.6608 MHz. Ba a zaɓi waɗannan mitoci tare da sassa na ƙima ba bisa ga ka'ida ba, amma sakamako ne da babu makawa na la'akari da ƙira dangane da ka'idojin sadarwa, mitar -ƙillacewar rarrabuwa, da tsarin{5}makamai na baya. An fara daga mahimman ƙa'idodi, wannan labarin yana nazarin dabaru na ƙirƙira na mitoci kaɗan kuma yana ba da hanyoyin dubawa masu amfani don zaɓin ɓangaren.
- Mahimman Ƙirar Ƙira na Mahimman Matsalolin Juzu'i
A matsayin tushen agogon tsarin, zaɓin mitar oscillator na crystal koyaushe ana keɓance shi don biyan madaidaitan buƙatun lokacin da'irori na dijital (kamar PLLs, masu rarrabawa, da sadarwar serial). Fitowar maki mitar juzu'i da farko ya samo asali ne daga nau'ikan ƙira iri huɗu masu zuwa:
1. Daidaita zuwa Rukunin Integer na UART don Tabbatar da Kuskure{1}} Ƙimar Baud Kyauta
Adadin baud na serial yana samuwa ne daga agogon tsarin ta hanyar rabon lamba, bisa ga dabara mai zuwa: Baud rate=Mitar agogo / Factor Factor
Don samar da daidaitattun daidaitattun ƙimar baud (kamar 9600, 19200, ko 115200 bps), mitar agogo dole ne a rarraba ta wurin mai rarrabawa ba tare da saura ba. Ɗaukar 1.8432 MHz a matsayin misali, bayan rarrabuwa mai ninki 16:
1.8432 MHz ÷ 16=115.2 kHz, wanda yayi daidai 115200 bps.
Hakazalika, 11.0592 MHz da 19.6608 MHz sau 6 ne da 10.666… sau 1.8432 MHz, bi da bi (a zahiri, 11.0592=1.8432 × 6, 19.6608=1.8432 × 10.666… yana buƙatar PLL), amma ya fi dacewa don amfani da su kai tsaye kamar yadda mitar agogon M1s{0}. ƙyale mai rarraba UART na ciki don samar da duk daidaitattun ƙimar baud ta hanyar rarraba. Idan aka zaɓi mitar lamba ta 20 MHz, ba za a iya raba shi daidai da 115,200 ba, yana haifar da kuskuren tarawa da haifar da kurakuran firam ko asarar fakiti.
2.Taimako don mitar binary{1}}tsararrun gine-gine yana sauƙaƙa ƙirar bishiyar agogo
Mitoci kamar 20.48 MHz, 10.24 MHz, da 5.12 MHz duk ana iya bayyana su azaman 2ⁿ 10 kHz (misali, 20.48 MHz=2048 × 10 kHz). Bayan watsa waɗannan mitoci ta hanyar rarraba mitar binary, ana iya samar da ƙananan yanki na agogo kamar 10.24 MHz, 5.12 MHz, 2.56 MHz, 1.28 MHz, da sauransu. Wannan tsarin yana da kyau{17}}ya dace da aiwatar da rarrabuwar mitoci ta amfani da ƙididdiga na binaryar ko rajistar canji, yana haifar da tsarin da'ira mai sauƙi tare da ƙayyadaddun alaƙar lokaci mai kyau da daidaitawar lokaci tsakanin mitoci daban-daban{19}}waɗanda aka raba agogo. Ana amfani da waɗannan mitoci akai-akai azaman mitoci na tushe a cikin DSPs na masana'antu, PLCs, da servo drives.
3. Haɗa ta hanyar PLL don saduwa da ƙayyadaddun hanyoyin sadarwar sauri da sauti/bidiyo
SoCs na zamani, na'urori masu gani, da na'urori masu sarrafa bidiyo sun haɗa PLLs, waɗanda galibi suna amfani da daidaitattun mitoci (kamar 25 MHz ko 24 MHz) azaman tunani sannan kuma suna haifar da takamaiman mitoci marasa {2}} ta hanyar rarraba lamba ko ninkawa, ko rarrabuwa. Misalai na yau da kullun sun haɗa da:
74.25 MHz: Maɗaukakin agogon samfurin bidiyo na - wanda aka ayyana ta hanyar SMPTE misali, ana amfani da shi don tsari kamar 1080i da 720p;
33.1776 MHz: Yawanci ana samun su a cikin codecs audio da broadband RF gaba{1}} ƙare; lokacin da aka yi amfani da shi tare da PLL, yana iya samar da daidaitattun iyalai masu ƙima na 44.1 kHz ko 48 kHz;
25.000625 MHz: Wasu PHYs na Ethernet suna amfani da agogon 25 MHz tare da PLL mai juzu'i don samar da madaidaicin adadin bayanai na 125 MHz don tallafawa ƙimar layin 1 Gbps (lura cewa yawan adadin adadin 25 MHz ana amfani dashi a aikace; ana bayar da wannan anan don dalilai kawai).
Ya kamata a lura cewa rabon mitar juzu'i yana gabatar da ƙayyadaddun jitter da sigina masu ɓarna. Don aikace-aikacen da ke da hayaniyar lokaci, yakamata a ba da fifiko ga mitoci masu niyya waɗanda za a iya samun su kai tsaye ta hanyar rarraba mitar lamba, ko don amfani da ƙaramar surutai{1} PLLs tare da ingantattun madauki na madauki daidai.
4.Adherence ga Ka'idojin Masana'antu na Tarihi da La'akari da EMC
Ka'idodin Tarihi: USB 2.0 yana ƙayyadaddun agogo mai tsayi 48 MHz -; Ethernet MACs suna amfani da 25 MHz ko 125 MHz; kuma ainihin agogon - (RTCs) suna aiki a 32.768 kHz (2¹⁵ Hz). An daidaita waɗannan mitoci lokacin da aka kafa ma'auni kuma tun daga lokacin an karbe su a duk faɗin sarkar masana'antu, sun zama ma'auni na gaskiya.
Daidaituwar Electromagnetic (EMC): Mafi girma{0}} oda masu jituwa na mitocin lamba na iya haɗuwa tare da samar da wutar lantarki, RF, ko igiyoyin sadarwa mara waya, suna gabatar da tsangwama. Zaɓin mitar oscillator tare da ɓangaren juzu'i na iya tarwatsa ko canza kuzarin jituwa, ta haka rage haɗarin EMI da rage farashin tacewa da garkuwa.
- Wasu Maɓalli Maɓalli a Zaɓin Crystal Oscillator
Baya ga ƙimar mitar, abubuwan injiniya masu zuwa suna da mahimmanci daidai don zaɓi:
Fashe Noise da Jitter
Ko da yake PLLs na iya haɗa kowane mitar, rarrabuwar mitar juzu'i tana raguwa sosai kusa da{0}} hayaniyar ƙarshen zamani da jitter bazuwar. Don aikace-aikace irin su manyan na'urorin gani na gani masu tsayi, millimita{3}} radar, ko 5G fronthaul, ana ba da shawarar zaɓin oscillators na kristal kai tsaye tare da mitoci na asali waɗanda suka dace da ƙayyadaddun hayaniyar lokaci don guje wa rashin isassun ƙimar ƙimar sigina daga baya.
Lokacin Jagora da Farashin
Matsakaicin mitoci na - ko na al'ada yawanci suna buƙatar dogon lokacin jagora kuma suna haifar da tsadar injiniya. A cikin iyakoki masu yarda da aiki, yakamata a ba da fifiko ga masana'antu daidaitattun mitoci (kamar mitoci gama-gari kamar 25 MHz, 27 MHz, 40 MHz, da 50 MHz, da madaidaitan mitoci da aka ambata a cikin wannan labarin) don taƙaita zagayowar R&D da sarrafa farashin BOM.
Daidaitawa tare da Mazabin Gida
A halin yanzu, masana'antun oscillator na quartz crystal na cikin gida sun rufe mafi yawan adadin adadin da aka saba amfani da su da mitoci na juzu'i. Lokacin zabar na'ura, mai da hankali kan kwanciyar hankali wadata, halayen zafin jiki (kamar ± 10 ppm da ± 20 ppm), da ma'aunin ƙarfin ɗaukar nauyi don tabbatar da dacewa tare da buƙatun shigar da agogo na guntu mai sarrafawa.
- Shawarwarin Zaɓin Zaɓuɓɓuka
Na farko,ƙayyade iyakokin agogon tsarin: Lissafin madaidaicin mitocin agogo da ake buƙata ta kowane yanki (UART, I2S, SPI, Ethernet, USB, Bidiyo) da hallasan kuskuren kuskuren su.
Samo ainihin mitar oscillator crystal a baya:Idan microcontroller yana da ginanniyar ginanniyar -a cikin PLL, zaɓi madaidaicin oscillator crystal wanda zai iya samar da mitoci masu niyya ta hanyar ƙima ko ƙarami{1}}arancin rabon rabo. Ba da fifiko ga mitoci tare da rabon rabo ƙasa da 100 da ƙima mai ƙarfi wanda ke da iko na 2.
Tabbatar da kuskuren rarraba: Yi ƙididdige ko kuskuren rarraba ya kasance ƙasa da matsakaicin matsakaicin ƙimar baud/sauran ƙimar ƙima da keɓaɓɓu (yawanci <±2%).
Tantance hadarin EMI:Yi nazari na bakan gizo na maɗaukakin jituwa mai girma{0}; idan ya cancanta, zaɓi wurin mitar da ya kauce daga lamba{1}} oda masu jituwa.
Yi la'akari da samuwa da farashi: Yayin saduwa da buƙatun aikin, zaɓi samfuri tare da wadatar kasuwa da wadatar kasuwa da nau'in fakiti (misali, HC-49S, SMD 3.2 × 2.5 mm) wanda ya dace da bukatun samarwa.