With the development of communication technology, handheld radio yuqori chastotali elektron karta texnologiya tobora ko’proq qo’llanilmoqda, masalan: simsiz peyjer, mobil telefon, simsiz PDA va boshqalar, radiochastota sxemasining ishlashi butun mahsulot sifatiga bevosita ta’sir qiladi. Bu qo’lda ishlaydigan mahsulotlarning eng katta xususiyatlaridan biri miniatyuralashdir va miniatyuralash shuni ko’rsatadiki, komponentlarning zichligi juda yuqori, bu esa komponentlarni (shu jumladan SMD, SMC, yalang’och chip va boshqalarni) bir -biriga juda ta’sirli qiladi. Agar elektromagnit parazit signali to’g’ri ishlatilmasa, butun elektron tizimi to’g’ri ishlamasligi mumkin. Shu sababli, elektromagnit shovqinni qanday oldini olish va bostirish, elektromagnit moslikni yaxshilash RF chastotali PCB dizaynida juda muhim mavzuga aylandi. Xuddi shu sxema, har xil PCB dizayn tuzilishi, uning ishlash ko’rsatkichi juda katta farq qiladi. Ushbu maqolada, elektromagnit moslik talablariga erishish uchun, elektron protsessorlari palma mahsulotlarining rf elektronli PCBini loyihalashda elektr zanjirining ishlashini qanday oshirish mumkinligi muhokama qilinadi.

1. Plitani tanlash

The substrate of printed circuit board includes organic and inorganic categories. Substratning eng muhim xossalari – dielektrik doimiy R,, tarqalish koeffitsienti (yoki dielektrik yo’qotilishi) Tan δ, issiqlik kengayish koeffitsienti CET va namlikni yutish. ε R affects circuit impedance and signal transmission rate. Yuqori chastotali sxemalar uchun o’tkazuvchanlik tolerantligi e’tiborga olinadigan birinchi va eng muhim omil bo’lib, past o’tkazuvchanlikka bardoshli substrat tanlanishi kerak.

2. PCB design process

Because Protel99 SE software is different from Protel 98 and other software, the process of PCB design by Protel99 SE software is briefly discussed.

① Because Protel99 SE adopts the PROJECT database mode management, which is implicit in Windows 99, so we should first set up a database file to manage the circuit schematic diagram and PCB layout designed.

② Design of schematic diagram. Tarmoqqa ulanishni amalga oshirish uchun ishlatilgan barcha komponentlar asosiy kutubxonadan oldin komponentlar kutubxonasida bo’lishi kerak; aks holda, kerakli komponentlar SCHLIB da tuzilishi va kutubxona faylida saqlanishi kerak. Keyin, siz komponentlar kutubxonasidan kerakli komponentlarni chaqirib, ularni mo’ljallangan sxemaga muvofiq ulashingiz mumkin.

③ After the schematic design is completed, a network table can be formed for use in PCB design.

④PCB design. A. CB shakli va hajmini aniqlash. The shape and size of PCB are determined according to the position of PCB in the product, the size and shape of the space and the cooperation with other parts. Draw the shape of the PCB using the PLACE TRACK command on MECHANICAL LAYER. B. SMT talablariga muvofiq PCBda joylashuv teshiklari, ko’zlari va mos yozuvlar nuqtalarini yarating. C. Production of components. If you need to use some special components that do not exist in the component library, you need to make components before layout. Protel99 SE -da komponentlarni tayyorlash jarayoni nisbatan oddiy. COMPONENT qilish oynasiga kirish uchun “DIZAYN” menyusidagi “MAKE KUTUBXONA” buyrug’ini tanlang, so’ng “TOOL” menyusidagi “YANGI KOMPONENT” buyrug’ini DESIGN komponentlariga tanlang. Bu vaqtda, tegishli PADni ma’lum bir joyga torting va uni kerakli PADga tahrir qiling (shu jumladan, PADning shakli, o’lchami, ichki diametri va burchagi va boshqalar) va PADning mos keladigan pin nomini belgilang. Haqiqiy komponentning shakli va hajmiga qarab PLACE PAD buyrug’i bilan TOP LAYER va boshqalar. Then use the PLACE TRACK command to draw the maximum appearance of the component in the TOP OVERLAYER, select a component name and store it in the component library. D. Komponentlar tayyorlangandan so’ng, sxemasi va simlari o’tkaziladi. Bu ikki qism quyida batafsil muhokama qilinadi. E. Check after the above procedure is complete. Bir tomondan, bu sxema printsipini tekshirishni o’z ichiga oladi, boshqa tomondan, bir -biriga mos kelishini va yig’ilishini tekshirish kerak. The circuit principle can be checked manually or automatically by network (the network formed by schematic diagram can be compared with the network formed by PCB). F. Tekshirilgandan so’ng, faylni arxivlang va chiqaring. Protel99 SE -da, FILE -ni belgilangan yo’lga va FILE -ga saqlash uchun FILE variantidagi EXPORT buyrug’ini ishga tushirish kerak (IMPORT buyrug’i – faylni Protel99 SE -ga import qilish). Eslatma: Protel99 SE “FILE” variantida “Nusxasini AS SAVE …” Buyruq bajarilgandan so’ng, tanlangan fayl nomi Windows 98 da ko’rinmaydi, shuning uchun fayl Resurs menejerida ko’rinmaydi. Bu Protel 98 -dagi “SAVE AS …” dan farq qiladi. Bu xuddi shunday ishlamaydi.

3. Components layout

SMT odatda komponentlarni payvandlash uchun infraqizil o’choqli issiqlik oqimini payvandlashdan foydalanganligi sababli, komponentlarning joylashuvi lehim bo’g’inlarining sifatiga, so’ngra mahsulotlarning chiqishiga ta’sir qiladi. For PCB design of rf circuit, electromagnetic compatibility requires that each circuit module does not generate electromagnetic radiation as far as possible, and has a certain ability to resist electromagnetic interference. Therefore, the layout of components also directly affects the interference and anti-interference ability of the circuit itself, which is also directly related to the performance of the designed circuit. Therefore, in the design of RF circuit PCB, in addition to the layout of ordinary PCB design, we should also consider how to reduce the interference between various parts of the RF circuit, how to reduce the interference of the circuit itself to other circuits and the anti-interference ability of the circuit itself. Tajribaga ko’ra, rf sxemasining ta’siri nafaqat chastotali elektron kartaning ishlash ko’rsatkichiga, balki protsessor platasi bilan o’zaro ta’sirga ham bog’liq. Shuning uchun, PCB dizaynida oqilona tartib ayniqsa muhimdir.

General layout principle: components should be arranged in the same direction as far as possible, and the bad welding phenomenon can be reduced or even avoided by selecting the direction of PCB entering the tin melt system; Tajribaga ko’ra, kalay erituvchi komponentlar talablarini qondirish uchun komponentlar orasidagi bo’shliq kamida 0.5 mm bo’lishi kerak. Agar tenglikni kartochkasining maydoni ruxsat bersa, komponentlar orasidagi bo’shliq imkon qadar keng bo’lishi kerak. Ikki tomonlama panellar uchun bir tomoni SMD va SMC komponentlari uchun, ikkinchi tomoni esa diskret komponentlar uchun mo’ljallangan bo’lishi kerak.

Note in layout:

* First determine the position of interface components on the PCB with other PCB boards or systems, and pay attention to the coordination of interface components (such as the orientation of components, etc.).

* Qo’lda ishlaydigan mahsulotlarning kichik hajmi tufayli komponentlar ixcham tarzda joylashtirilgan, shuning uchun kattaroq komponentlar uchun tegishli joyni aniqlash va bir -birining harakatini muvofiqlashtirish muammosini ko’rib chiqish kerak.

* O’chirish oqimini va kuchsiz oqim signalini, alohida raqamli signal pallasini va analog signalni ajratish uchun imkon qadar iloji boricha sxemani diqqat bilan tahlil qilish, blokni qayta ishlash (yuqori chastotali kuchaytirgich davri, aralashtirish davri va demodulyatsiya davri va boshqalar). kontaktlarning zanglashiga olib keladigan, xuddi shu funktsiyani bajaring, ma’lum bir diapazonda joylashtirilishi kerak, shu bilan signalning aylanish doirasi kamayadi; Zanjirning har bir qismining filtrlash tarmog’i yaqin atrofga ulangan bo’lishi kerak, shunda kontaktlarning zanglashiga qarshi qobiliyatiga ko’ra, nafaqat nurlanishni kamaytirish, balki aralashish ehtimolini ham kamaytirish mumkin.

* Foydalanishda elektromagnit moslashuvga sezgirligi bo’yicha hujayra zanjirlari. The components of the circuit that are vulnerable to interference should also avoid interference sources (such as interference from the CPU on the data processing board).

4. Elektr kabellari

After the components are laid out, wiring can begin. The basic principle of wiring is: under the condition of assembly density, low-density wiring design should be selected as far as possible, and signal wiring should be as thick and thin as possible, which is conducive to impedance matching.

Rf davri uchun signal chizig’ining yo’nalishi, kengligi va chiziq oralig’ining asossiz dizayni signal uzatish uzatish liniyalari orasidagi shovqinni keltirib chiqarishi mumkin; Bundan tashqari, tizimning quvvat manbai shovqin aralashuviga ham ega, shuning uchun PCB chastotasini loyihalashda oqilona simlarni har tomonlama ko’rib chiqish kerak.

Kabellarni ulashda, barcha simlar tenglikni kartochkalari chegarasidan uzoqda bo’lishi kerak (taxminan 2 mm). Quvvat liniyasi pastadir qarshiligini kamaytirish uchun imkon qadar kengroq bo’lishi kerak. Shu bilan birga, elektr uzatish liniyasi va er chizig’ining yo’nalishi shovqinlarga qarshi qobiliyatini yaxshilash uchun ma’lumotlarni uzatish yo’nalishiga mos kelishi kerak. Signal chiziqlari iloji boricha qisqa bo’lishi va teshiklar sonini iloji boricha kamaytirish kerak. Komponentlar orasidagi aloqa qanchalik qisqa bo’lsa, parametrlarning taqsimlanishini va bir -birining orasidagi elektromagnit shovqinni kamaytirish yaxshi bo’ladi; For incompatible signal lines should be far away from each other, and try to avoid parallel lines, and in the positive two sides of the application of mutual vertical signal lines; Wiring in need of corner address should be 135° Angle as appropriate, avoid turning right angles.

The line directly connected with the pad should not be too wide, and the line should be away from the disconnected components as far as possible to avoid short circuit; Holes should not be drawn on components, and should be far away from disconnected components as far as possible to avoid virtual welding, continuous welding, short circuit and other phenomena in production.

In PCB design of rf circuit, the correct wiring of power line and ground wire is particularly important, and reasonable design is the most important means to overcome electromagnetic interference. Quite a lot of interference sources on PCB are generated by power supply and ground wire, among which ground wire causes the most noise interference.

Topraklama simining elektromagnit parazitga olib kelishi oson bo’lishining asosiy sababi – er simining impedansi. When a current flows through the ground, a voltage will be generated on the ground, resulting in the ground loop current, forming the loop interference of the ground. When multiple circuits share a single piece of ground wire, common impedance coupling occurs, resulting in what is known as ground noise. Therefore, when wiring the ground wire of the RF circuit PCB, do:

* Birinchidan, sxema bloklarga bo’linadi, rf davri asosan yuqori chastotali amplifikatsiya, aralashtirish, demodulyatsiya, mahalliy tebranish va boshqa qismlarga bo’linishi mumkin, shuning uchun har bir elektron modulli elektron topraklama uchun umumiy potentsial mos yozuvlar nuqtasini beradi. signal har xil elektron modullar o’rtasida uzatilishi mumkin. Keyin RF chastotali PCB erga ulangan nuqtada umumlashtiriladi, ya’ni asosiy poydevorda umumlashtiriladi. Since there is only one reference point, there is no common impedance coupling and thus no mutual interference problem.

* Raqamli maydon va analog zonani iloji boricha topraklama simini izolyatsiyalash, va raqamli er va analogli topraklamani ajratish uchun, nihoyat, elektr tarmog’iga ulangan.

* Zanjirning har bir qismidagi topraklama simlari, shuningdek, bitta nuqtali topraklama tamoyiliga e’tibor berishi, signal uzatish maydonini minimallashtirishi va yaqin atrofdagi filtr filtrining tegishli manziliga to’g’ri kelishi kerak.

* Agar bo’sh joy ruxsat bersa, signalni bir -biriga ulashining oldini olish uchun har bir modulni tuproqli sim bilan ajratish yaxshiroqdir.

5. Xulosa

RF PCB dizaynining kaliti radiatsiya qobiliyatini qanday kamaytirish va interferentsiyaga qarshi qobiliyatni yaxshilashda yotadi. Aqlli tartib va ​​simlar – bu RF PCB ni loyihalashning kafolati. Ushbu maqolada tasvirlangan usul chastotali PCB konstruktsiyasining ishonchliligini oshirish, elektromagnit parazit muammosini hal qilish va elektromagnit moslik maqsadiga erishish uchun yordam beradi.