In PCB wiring, yana faruwa sau da yawa cewa dole ne a yi amfani da layin sirara don wucewa ta wurin da ke da ƙarancin sararin wayoyi, sannan a dawo da layin zuwa faɗinsa na asali. Canji a fadin layin zai haifar da canjin rashin ƙarfi, wanda zai haifar da tunani kuma ya shafi siginar. Don haka yaushe za mu iya yin watsi da wannan tasirin, kuma yaushe ne za mu yi la’akari da tasirin sa?

Abubuwa guda uku suna da alaƙa da wannan tasirin: girman canjin rashin ƙarfi, lokacin tashin siginar, da jinkirin siginar a kan kunkuntar layi.

Na farko, ana tattauna girman canjin rashin isasshen. Tsarin ƙirar da’irori da yawa yana buƙatar ƙarar da aka nuna ta zama ƙasa da 5% na jujjuyawar wutar lantarki (wanda ke da alaƙa da ƙarar kasafin kuɗi akan siginar), bisa ga tsarin daidaiton tunani:

Ana iya ƙididdige ƙimar canjin ƙalubalen azaman △ Z/Z1 ≤ 10%. Kamar yadda wataƙila kun sani, mai nuna alamar rashin ƙarfi a kan allo shine +/- 10%, kuma shine tushen abin.

Idan sauye -sauyen rashin daidaituwa ya faru sau ɗaya kawai, kamar lokacin da faɗin layin ya canza daga 8mil zuwa 6mil kuma ya kasance 6mil, canjin ƙarancin dole ne ya zama ƙasa da 10% don isa ga buƙatun kasafin kuɗin hayaniya cewa siginar ta nuna hayaniya a canjin canji kada ya wuce 5% na jujjuyawar wutar lantarki. Wannan wani lokacin yana da wahalar yi. Dauki misalin layukan microstrip akan faranti na FR4 a matsayin misali. Bari mu lissafa. Idan faɗin layin shine 8mil, kauri tsakanin layin da jirgin da ake tunani shine 4mil kuma rashin halayyar halayyar shine 46.5 ohms. Lokacin da faɗin layin ya canza zuwa 6mil, ƙarancin halayen ya zama 54.2 ohm, kuma canjin canjin ya kai 20%. Amplitude na siginar da aka nuna dole ne ya wuce matsayin. Dangane da tasirin tasiri akan siginar, amma kuma tare da lokacin tashin siginar da jinkirin lokaci daga direba zuwa siginar ma’ana. Amma aƙalla wuri ne mai yuwuwar matsala. Abin farin ciki, zaku iya warware matsalar tare da tashoshin da ba daidai ba.

Idan canjin rashin ƙarfi ya faru sau biyu, alal misali, faɗin layin yana canzawa daga 8mil zuwa 6mil, sannan ya canza zuwa 8mil bayan cire 2cm. Sannan a cikin tsayin 2cm mai tsawon 6mil mai faɗi a ƙarshen ƙarshen tunani, ɗayan shine rashin ƙarfi ya zama mafi girma, kyakkyawan tunani, sannan ƙarancin ya zama ƙarami, tunani mara kyau. Idan lokacin tsakanin tunani yayi gajarta, tunani biyu na iya soke juna, rage tasirin. Da ɗauka cewa siginar watsawa ita ce 1V, 0.2V yana nunawa a cikin kyakkyawan tunani na farko, 1.2V ana watsa shi gaba, kuma -0.2*1.2 = 0.24V yana nuna baya a cikin tunani na biyu. Tunanin cewa tsawon layin 6mil ya takaice sosai kuma tunani biyu na faruwa kusan lokaci guda, jimlar ƙarfin wutar lantarki shine kawai 0.04V, ƙasa da buƙatun kasafin kuɗi na 5%. Sabili da haka, ko kuma nawa wannan tasirin ke shafar siginar ya dogara da jinkirin lokaci a canjin impedance da lokacin tashin siginar. Nazarin da gwaje -gwajen sun nuna cewa muddin jinkirin da aka samu a canjin rashin isasshen ƙasa da kashi 20% na lokacin tashin siginar, siginar da aka nuna ba zata haifar da matsala ba. Idan lokacin tashin siginar shine 1ns, to jinkirin a canjin rashin isasshen ƙasa da 0.2ns daidai da inci 1.2, kuma tunani ba matsala bane. A takaice dai, a wannan yanayin, tsawon waya mai nisan mil 6 na ƙasa da 3cm bai kamata ya zama matsala ba.

Lokacin da faɗin wayoyin PCB ya canza, yakamata a bincika sosai gwargwadon ainihin yanayin don ganin ko akwai tasiri. Akwai sigogi uku da za a damu da su: nawa ne rashin isasshen canji ke canzawa, tsawon lokacin siginar ta tashi, da kuma tsawon lokacin da sashi mai kama da wuyan sashin layin ke canzawa. Yi ƙima mai ƙima bisa ga hanyar da ke sama kuma bar ɗan gefe kamar yadda ya dace. Idan za ta yiwu, yi ƙoƙarin rage tsawon wuyan.

Ya kamata a nuna cewa a cikin ainihin aikin PCB, sigogi ba za su iya zama daidai ba kamar waɗanda ke cikin ka’idar. Ka’idar na iya ba da jagora don ƙirar mu, amma ba za a iya kwafa ko ƙaƙƙarfan ra’ayi ba. Bayan haka, wannan ilimin kimiyya ne. Ya kamata a sake kimanta ƙimar da aka ƙaddara bisa ga ainihin yanayin, sannan a yi amfani da ƙirar. Idan kun ji rashin ƙwarewa, ku kasance masu ra’ayin mazan jiya kuma ku daidaita da farashin ƙira.